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Normally, is known as electric flux., unit : N m2 C-1, 1.2.1. What is meant by quantisation of charges?, The charge q is equal to an integral multiple 1.2.11.Differentiate Polar and Non polar Molecule, of fundamental charge e. q = ne, 1.2.2. What are the differences between Coulomb force, and gravitational force?, , 1. Electrostatics, , 1.2.3. What are the properties of ‘Electric field lines’?, 1) Electric field lines start from positive charge and, end at negative charge., 2) Electric field lines never intersect., 3) Tangent of the electric field line gives the, direction of electric field., 4) If electric field is large , electric field lines are, closer. If electric field is less , electric field lines are, apart., 5) Number of electric field lines is proportional to, charge., 1.2.4. The electric field lines never intersect. Justify., Two electric fields pointing in two different, directions at a single point cannot be possible. So,, electric field lines never intersect, 1.2.5. What is corona discharge, Reduction of total charge of the conductor, near the sharp edge is called action at points or corona, discharge., 1.2.6.During lightning it is safer to sit inside a bus than, in open ground or under a tree.why?, 1) Electric field inside a bus is zero., 2) Bus provides electrostatic shielding., 3) During lightning, the charges flow through the, body of the conductor to the ground with no, effect on the person inside that bus., 1.2.7.State Gauss Law, The total electric flux 𝛟 E through a, closed surface is equal to 1/𝜀 0 times, net charge in the surface., 1.2.8. Write down the Applications of capacitors, 1. Used in flash camera for releasing energy., 2. Used in heart defibrillator, 3. Used in the ignition system of automobile engines, to eliminate sparking, 4. Used to reduce power fluctuations in power, supplies, 1.2.9. Define ‘Electric dipole’, Two equal and opposite charges separated by a, small distance constitute an electric dipole., Examples:, CO,, water,, ammonia,, HCl, 1.2.10. Define electric flux., Total number of electric field lines crossing a area, 1.Electrostatics, , 1.2.12. What is the general definition of electric dipole, moment?, Dipole moment is equal to product of, magnitude of charge and distance. p=q.2a.Unit :C m, 1.2.13. What is an equipotential surface?, If All the points of a surface are at same, potential, then the surface is called equipotential, surface., 1.2.14. What are the properties of an equipotential, surface?, 1) Work done to move a charge on, equipotential surface is Zero., 2) Electric field is normal to equipotential, surface., 1.2.15. Give the relation between electric field and, electric potential., 1.2.16. Define ‘electrostatic potential energy?., Work done to assemble the system of, charges in a configuration is Electrostatic potential, energy., 1.2.17. What is meant by electrostatic energy density?, Electric Energy stored per unit volume is called, electrostatic energy density., 1.2.18. Write a short note on ‘electrostatic shielding’., Protecting a particular space from external, field is called electrostatic shielding., 1.2.19.Define ‘capacitance’. Give its unit., Ratio of the magnitude of charge on any one, of the conductor plates to the potential difference, between the conductors, is the capacitance C of a, capacitor. unit: Farad, 1.2.20. What is meant by superposition principle., Total force on a charge is equal to vector, sum of all forces acting on the charge., 1.2.21. Define ‘Electric field’., Force experienced by a unit charge at a point, is known as electric field unit: NC-1, 1.2.22 Define ‘electrostatic potential”., Work done by an external force to bring a, unit positive charge with constant velocity from, infinity to the point, is electrostatic potential at that, point. unit: volt, , S.Jayachandran, PG.Asst,GHSS,Manali,Thiruvallur Dt, , 9840430109, , Page 1

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1.2.23. What is Polarisation?, 1.3.3 Obtain an expression for potential energy due to, Total dipole moment per unit volume of, a collection of Two charge and three-point charges, dielectric is known as polarization. unit: Cm-2, which are separated by finite distances., 1.2.24 Write down Coulomb’s law in vector form and, mention what each term represents., 1)The force exerted on charge 𝑞1 by charge 𝑞2 is, , 𝑟̂, 21 is a unit vector from charge 𝑞2 to charge 𝑞1, 2)The force exerted on charge 𝑞2 by charge 𝑞1 is, , 𝑟̂, 12 is a unit vector from charge 𝑞1 to charge 𝑞2, , 1.3.1 Derive an expression for electrostatic potential, due to a point charge., Work done to move a positive charge from, infinity to a point with constant velocity is the Potential Energy of a, system, :, electric potential at that point., of Three charges, P is a point at a distance r from the charge q., 1.3.4 Obtain the expression for capacitance for a, parallel plate capacitor., Consider a capacitor with two parallel plates, each of cross-sectional area A and separated by a, distance, , 1.3.2 Derive an expression for Torque experienced by, an electric dipole in the uniform electric field, An electric dipole of dipole moment p is placed, in a uniform electric field. Two forces qE and _-qE, act on +q and -q. The total force acting on the dipole, is zero. These two forces acting at different points, will constitute a couple and the dipole experience a, 1.3.5 Explain in detail Coulomb’s law and its aspects., torque., This torque rotates the 1.Electrostatic force is directly proportional to the, dipole and aligns it product of two charges and is inversely, proportional to the square of the distance between, with the electric field, the two charges., 2.Electrostatic force is along the line joining the two, charges., 3.Coulomb’s law is similar as Newton’s law of, gravitation., 4.Electrostatic force is always greater than, gravitational force, 5.Electrostatic force depends on nature of the, medium., 6.Coulomb force is true only for point charges., 1.Electrostatics, , S.Jayachandran, PG.Asst,GHSS,Manali,Thiruvallur Dt, , 9840430109, , Page 2

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1.3.6 Derive the expression for resultant capacitance,, when capacitors are connected in series ., Three capacitors of capacitance C1, C2 and C3, connected in series with a battery of voltage V., Each capacitor stores the same charge Q. Voltage, across each capacitor V1, V2 and V3 are different., , If initial position Ɵ’ = 900, Potential energy stored in dipole, kept in the uniform electric field, 1.3.7 Derive the expression for resultant capacitance,, when capacitors are connected in parallel., Three capacitors of capacitance C1, C2 and C3, connected in parallel with a battery of voltage V, Voltage across each capacitor is Same as V., Each capacitor stores different charges Q 1, Q2, Q3, , 1.3.9 Obtain the expression for energy density of a, Parallel plate capacitor, Capacitor stores charge and energy. To, store the charge, work is done by the battery. This, work done is stored as electrostatic potential energy, 𝑼𝑬 in the capacitor., , 1.3.10 Explain in detail the effect of a dielectric placed, in a parallel plate capacitor, 1.3.8 Derive an expression for electrostatic potential, energy of the dipole in a uniform electric field, An electric dipole of dipole moment p, is placed in the uniform electric field E. The dipole, experiences a torque which rotates the dipole to, align along the electric field., To rotate the dipole against the torque, an, equal and opposite external torque must be applied on, the dipole., The work done by external torque to rotate the, dipole from angle Ɵ′ to Ɵ at constant angular velocity, is, 1.Electrostatics, , S.Jayachandran, PG.Asst,GHSS,Manali,Thiruvallur Dt, , 9840430109, , Page 3

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1.5.1Calculate the electric field due to a dipole on its, axial line, An electric dipole is placed along the X-axis. C is a, point at a distance r from O on the axial line., , Direction of Electric field is opposite to dipole, moment., 1.5.3 Derive an expression for electrostatic potential, due to an electric dipole., An electric dipole is placed along the X-axis., P is a point at a distance r from O., , 1.5.2 Calculate the electric field due to a dipole on its, equatorial plane, An electric dipole is placed along the Xaxis. C is a point at a distance r from O on the, equatorial plane., , The direction of ⃗⃗⃗⃗, 𝐸+ is along BC and the, direction of ⃗⃗⃗⃗, 𝐸− is along CA.On resolving, Vertical components𝐸+ Sinθ and 𝐸− Sinθ are, equal and opoosite. So, they cancel each other., HorizontalComponents𝐸+ Cosθ and𝐸− Cosθ, add together to give resultant Electric field., 1.Electrostatics, , S.Jayachandran, PG.Asst, GHSS, Manali, Thiruvallur Dt, , 9840430109, , Page 4

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1.5.4 Explain in detail the construction and working, of a Van de Graaff generator., Device produces potential difference of 107 V., Principle: Electrostatic induction and action at, points., Construction:, 1. A hollow spherical conductor is fixed on the, insulating stand., 2. A pulley B is placed at the center of the hollow, sphere and another pulley C is fixed at the, bottom., 3. A belt made up of silk or rubber runs over both, pulleys., 4. The pulley C is run by the electric motor., 5. Two metallic combs E and D are fixed near the, pulleys., 6. The comb D is given potential of 104 V., 7. The upper comb E is connected to the inner sphere., , Working, 1. High electric field near comb D, ionizes the air., 2. Due to action of points, belt gets positive, charges and negative charges are attracted, towards the comb D., 3. When the positive charges reach the comb E, Due, to electrostatic induction , Comb E gets, negative charge and sphere gets positive, charge., 4. The positive charges are distributed uniformly on, the outer surface of the hollow sphere., 5. Due to corona discharge , positive charges in the, belt are cancelled and down going belt does not, carry charge., 6. At the bottom, it again gains a large positive, charge., 7. This process continues till sphere produces the, potential difference of 107 V., 8. The leakage of charges can be reduced by enclosing, the machine in a gas filled steel chamber at very, high pressure., Uses, The high voltage produced is used to, accelerate positive ions (protons and deuterons) for, nuclear disintegrations., 1.5.4 Obtain the expression for electric field due to an, infinitely long charged wire., Consider, an infinite long straight wire having linear charge, 1.Electrostatics, , density λ(charge present per unit length). Let P be, a point at a distance r from the wire., The resultant electric field will be same at, all points equidistant from the wire and directed, radially outwards., A cylindrical Gaussian surface of radius r and, length L is taken., , If wire is negative charged, E acts inwards and if, wire is positive charged, E acts outwards., 1.5.4 Obtain the expression for electric field due to an, infinitely long charged sheet, Consider an infinite plane sheet of charges, with uniform surface charge density σ (charge, present per unit area). Let P be a point at a distance, of r from the sheet., Resultant electric field is same at all points, equidistant from the plane and radially directed, outward at all points., A cylindrical Gaussian surface of length 2r, and two flats surfaces each of area A is taken., , S.Jayachandran, PG.Asst, GHSS, Manali, Thiruvallur Dt, , 9840430109, , Page 5

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Case 3. At a point inside the spherical shell (r < R), Since Gaussian surface encloses no charge, Q = 0., No charge is present inside the sphere.electric field is, zero at all points inside the shell., , 1.5.4 Obtain the expression for electric field due to an, charged spherical sheel., Consider a uniformly charged spherical, shell of radius R carrying total charge Q. Let P be, a point at a distance of r from the centre of sphere., , Case 1. At a point outside the shell (r > R), , a spherical Gaussian surface of radius r is taken., , 1.3.11 Discuss the various properties of conductors in, electrostatic equilibrium., 1. The electric field is zero everywhere inside the, conductor., 2. There is no net charge inside the conductors. The, charges must reside only on the surface of the, conductors., 3. The electric field outside the conductor is, perpendicular to the surface of the conductor, and has a magnitude of σ/ε0 where σ is the, surface charge density at that point., 4. The electrostatic potential has the same value, on the surface and inside of the conductor., 1.3.12Explain in detail the principle behind the, lightning conductor., Lightning conductor is a device used to protect tall, buildings from lightning strikes., principle : Action at points or corona discharge., This device consists of a long thick copper, rod passing from top of the building to the ground., The upper end of the rod has a sharp spike or a, sharp needle. The lower end of the rod is connected, to copper plate which is buried deep into the ground., Working:, 1. When a negatively charged cloud is passing, above the building, it induces a large positive, charge on the spike., 2. Due to corona discharge, positive charge ionizes, the surrounding air, 3. This ionization neutralizes the negative charge, in the cloud., 4. The negative charge pushed to the spikes passes, through the copper rod andis safely diverted to the, Earth., 1.3.13 Deduce coulombs law from Gauss law, , Case 2. At a point on the surface of the spherical, shell (r = R), The electrical field at points, on the spherical shell, 1.Electrostatics, , S.Jayachandran, PG.Asst, GHSS, Manali, Thiruvallur Dt, , 9840430109, , Page 6

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Resistance of a conductor is equal, to ratio of Voltage applied to current, 2.2.1Why current is a scalar?, Current has both magnitude and direction .But flowing in the conductor., the direction of current does not obey vector laws of 2.2.11. Why touching a electrical connection with the, wet skin is always dangerous ., addition .So, Current is a scalar quantity., Resistance of dry skin is high around 500 k Ω., 2.2.2 Distinguish between drift velocity and mobility., But when the skin is wet, the resistance decreases to, Drift velocity, Mobility, Average velocity, Magnitude of the drift around 1000 Ω. While touching electric components, with wet hand, due to low resistance, large current, acquired by the electrons velocity per unit, flows in our body which is dangerous, in an Electric field., Electric field., 2.2.12.Is battery a source of electrons?, Vectot Quantity, Scalar Quantity, -1, 2 -1 -1, No, Battery is a source of electrical energy, due to, Unit: ms, mV s, which these electrons in the conducting wire flow in, 5. What are ohmic and non ohmic devices?, a particular direction., Ohmic Devices, Non Ohmic Devices, Materials or devices that, Materials or devices that 2.2.13.What is meant by internal resistance of a cell?, Resistance given by electrodes and electrolyte, obey Ohm’s law, do not obey Ohm’s law, A Graph of I against V is A Graph of I against V of a battery against the flow of charges within the, battery, is called internal resistance r of a cell., linear(Straight Line), is non-linear, 2.2.14. State Joule’s law of heating., 2.2.3. Define electrical resistivity., Heat developed in an electrical circuit is directly, Resistance of a conductor of unit length and, unit area of cross section is known as electrical proportional to, 1. square of the current, resistivity ρ of a material ., 2. resistance of the circuit and, Unit: ohm-metre (Ω m)., 3. time of flow of current., 2.2.4. Define temperature coefficient of resistance., Ratio of increase in resistivity per degree rise 2.2.15. What is Seebeck effect?, In a closed circuit made of two dissimilar, in temperature to its resistivity at To., metals, when the junctions are maintained at, Unit : per 0C., different temperatures an emf is developed., 2.2.5.State Kirchhoff’s current rule., 2.2.16. What is Thomson effect?, Algebraic sum of the currents at any junction, If two points in a conductor are at different, of a circuit is zero., temperatures, electron density changes at them. So,, 2.2.6.State Kirchhoff’s voltage rule., potential difference is created between these points., In a closed circuit the algebraic sum of the, 2.2.17. What is Peltier effect?, products of the current and resistance is equal to the, When current is passed through a, algebraic sum of emf in the circuit., thermocouple, heat is evolved at one junction and, 2.2.7. What is superconductivity?, absorbed at the other junction., Ability of certain materials to conduct at Zero, 2.2.18. State the applications of Seebeck effect., resistance with persistent current at very low, 1.Seebeck effect is used in thermoelectric, temperature is called superconductivity., generators, to convert waste heat into electricity., 2.2.8. What is electric power and electric energy?, 2.Used in automobiles for increasing fuel efficiency., Electrical power P is the rate at which the, 3.Used in thermocouples to measure the temperature, electrical potential energy is used. Unit: watt, difference., Electric energy is the product of electric Power, 2.2.19. What is the use of Fuse Wire., and Time. Unit: Watt hour, Fuse wire is connected in series in a circuit to protect, 2.2.9. Define current density., the electric devices from the heat developed. when a, Current per unit area of cross section of the, very large current passes through it. It has low melting, conductor iscalled current density (J). Unit: A m2, point material. It melts and breaks the circuit if, 2.2.10. State ohm’s Law, current exceeds a certain value., , 2.CURRENT ELECTRICITY, , 2.Current Electricity, , S.Jayachandran, PG.Asst, GHSS, Manali,Thiruvallur Dt, , 9840430109, , Page | 7

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2.2.20State the principle of potentiometer, connected to the central terminal E through a, The emf of the cell is directly proportional to the galvanometer (G) and a high resistance (HR). A, balancing length., Lechlanche cell and a key (K) are connected across the, 2.2.21Derive the expression for power P=VI in ends of the bridge wire., electrical circuit and write its various forms, The jockey is adjusted on the wire so that the, galvanometer shows zero deflection. Let the point be, J. The lengths AJ=l1 and JB=l2 of the bridge wire now, 2.2.22What is electric power and electric energy?, replace the resistance R and S of the Wheatstone’s, Electric Power is equal to rate at which, bridge. r is the resistance per unit length of wire, electrical energy is supplied. Unit watt., Electric Energy is equal to the product of electric, power and time. unit joule or kW h, 2.3.1. Obtain the condition for bridge balance in, Wheatstone’s bridge., , 2.3.4. How the emf of two cells are compared using, potentiometer?, To compare the emf of two cells, connections are, given as in the circuit. The first cell whose emf is 𝜺𝟏 is, included in the circuit and Balancing length l 1 is found., , 2.3.2 Explain the determination of the internal resistance, Next, the Second cell whose emf is 𝜺𝟐 is included in the, of a cell using voltmeter., The emf of cell ε is measured by connecting a circuit and Balancing length l 2 is found., high resistance voltmeter across it in a open circuit., The voltmeter reading gives the emf of the cell., External resistance R is included in the circuit, and current I flows in the circuit. The potential, difference across R is equal to the potential, difference across the cell (V)., , 2.3.5 Obtain the macroscopic form of Ohm’s law from, its microscopic form and discuss its limitation., l is the length and A is cross sectional area of, a wire. V is the potential difference applied across the, wire. E is the net electric field in the wire., By microscopic form of ohm’s law, , 2.3.3.Explain the determination of unknown resistance, using meter bridge., Meter bridge consists of one meter manganin, wire AB connected between copper strips Cand D., Unknown resistance P is connected in gap G1 and a This is the macroscopic form of ohm’s law. This law, Known resistance Q is connected in gap G2. A jockey is, cannot be applied for Non-Ohmic Materials., 2.Current Electricity, , S.Jayachandran, PG.Asst, GHSS, Manali,Thiruvallur Dt, , 9840430109, , Page | 8

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2.5.1 Describe the microscopic model of current and, obtain general form of Ohm’s law, A is the area of cross section of a conductor, E is, the applied electric field. n is the number of free, electrons per unit volume. vd is the drift velocity of, the free electrons., , Equivalent resistance is the sum of the individual, resistances, 2)Three Resistors of resistance R1, R2 and R3, connected in Parallel with a battery of voltage V., Voltage across each Resistor is Same.Different, Current I1,I2 and I3.are flowing through each resistors., , current density ( J ) is defined as the current per unit, area of cross section of the conductor ., , 2.5.3 Explain the determination of the internal, resistance of a cell using potentiometer., Connections are given as in the circuit to, determine the internal resistance of a cell., With K2 open, no current, flows in resistor R, so it, 𝜎 is conductivity of the material of the conductor, This equation is called microscopic form of ohm’s law. becomes open circuit., 2.5.2. Explain the equivalent resistance of a series and Let CJ = l1 is the balancing, length for the emf,, parallel resistor network., Three Resistors of resistance R1, R2 and R3, connected in series with a battery of voltage V., Same Current passes through each Resistor. When key K2 is closed, current flows in resistor R, so, Voltage across each resistor V1, V2 and V3 are it becomes closed circuit., different., , 2.Current Electricity, , S.Jayachandran, PG.Asst, GHSS, Manali,Thiruvallur Dt, , 9840430109, , Page | 9

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3.2.11. Define coercivity., Magnitude of the reverse magnetising field, for which the residual magnetism vanishes is called, 3.2.1. State Coulomb’s inverse law in magnetism., coercivity., Force of attraction or repulsion between two 3.2.12.State Tangent law, magnetic poles is directly proportional to the, When a magnetic needle is suspended in two, product of their pole strengths and inversely, perpendicular magnetic fields, it will come to rest, proportional to the square of the distance between in the direction of the resultant of the two fields., them., 3.2.13.Define intensity of magnetization., 3.2.2. State Ampere’s circuital law., Net magnetic moment per unit volume of the, Line integral of magnetic field over a closed, material is known as intensity of magnetization., loop is equal to μ0 times net current enclosed by the, 3.2.14. Define Declination, loop., The angle between magnetic meridian and, 3.2.3. Define magnetic dipole moment., geographical, meridian is called the magnetic, Product of pole strength and magnetic length of, declination, (D)., a magnet is called magnetic dipole moment 𝒑𝒎., direction of 𝒑𝒎 acts from south to north pole. 3.2.15.Define Dip, The angle between Earth’s total magnetic, ., Unit: 𝐀 𝐦𝟐, field and the horizontal direction in the magnetic, 3.2.4. What is magnetic susceptibility?, meridian is called dip or magnetic inclination (I), Ratio of the Intensity of magnetisation, 3.2.16.Define Curie Temperature, induced to the magnetising field., The temperature at which ferromagnetic, 3.2.5. What is meant by hysteresis?, material, becomes paramagnetic is known as Curie, Phenomenon of lagging of magnetic, induction behind the magnetising field is called temperature., hysteresis., 3.2.17.Why Steel and Alnico are used to make, 3.2.6. What is magnetic permeability?, Permanent magnets?, Ability of the material to allow the passage of, Steel and Alnico have high retentivity, high, magnetic field lines to pass through it., coercivity and high permeability. So they are, 3.2.7 Maxwell’s right hand cork screw rule, suitable for making permanent magnets., A right-handed screw is advanced along the 3.2.18.Why Soft iron and Mumetal are used to make, direction of current, the direction of rotation of the Electro magnets?, screw gives the direction of the magnetic field., Soft iron and Mumetal have high initial, 3.2.7.State Right hand thumb rule, permeability, low retentivity, low coercivity and thin, Current carrying conductor is held in right hand hysteresis loop with smaller area. So, they are used to, such that the thumb points in the direction of current make electromagnets., , then the fingers encircling the wire gives the 3.2.19.Why Soft iron is used to make Core of the, direction of the magnetic field lines produced., transformer, 3.2.7.State Right hand palm rule, Soft iron has high initial permeability, large, The current carrying solenoid is held in right magnetic induction and thin hysteresis loop with, hand such that fingers curl in the direction of smaller area., current, then extended thumb gives the direction of 3.2.20.How a galvanometer is converted into an, magnetic field, ammeter., 3.2.8. Define magnetic flux., By connecting a low resistance in parallel, Number of magnetic field lines crossing per with the galvanometer, unit area normally is called magnetic flux. Unit: weber 3.2.21. How a galvanometer is converted into a, 3.2.9. State Biot-Savart’s law., voltmeter., Magnitude of magnetic field varies, By connecting high resistance Rh in series, (i) directly as the current I, with galvanometer., (ii) directly as the length of current element, 3.2.22.Define Current sensitivity of a galvanometer, (iii) directly as sine of the angle between Idl and r., Deflection produced per unit current flowing, (iv) inversely as the square of the distance r., through a Galvanometer., , 3.Magnetism and Magnetic effects of, electric current, , 3.2.10.Define retentivity., Ability of the materials to retain magnetism, in them even after magnetising field vanishes., , 3.2.23 What is resonance condition in cyclotron?, frequency f at which the positive ion, circulates in the magnetic field must be equal to the, , 3.Magnetism and Magnetic Effects of Current S.Jayachandran, GHSS,Manali,Thiruvallur Dt,, , 9840430109, , Page | 10

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constant frequency of the electrical oscillator fosc., This is called resonance condition, 3.2.24.How to increase Current sensitivity of a, Galvanometer, 1) by increasing the number of turns N, 2) by increasing the magnetic induction B, 3) by increasing the area of the coil A, 4) by decreasing the couple per unit twist of the, suspension wire ., 3.2.25.Why Phosphor - bronze wire is used as the, suspension wire in a galvanometer, Phosphor - bronze wire has very small couple per, unit twist., 3.2.26 Is an ammeter connected in series or parallel in, a circuit? Why?, An ammeter is a low resistance instrument, which is always connected in series to the circuit., ammeter will not change current largely in the, circuit. If ammeter is connected in parallel, due to low, resistance large current will flow in it thereby, decreasing current in the main circuit, 3.3.1. Write the Properties of Magnetic field lines, 1) Magnetic field lines are continuous closed curves., 2) The tangent to the magnetic field lines gives the, direction of magnetic field at any point., 3) Magnetic field lines never intersect each other., 4) When the magnetic field is strong, magnetic field, lines are crowded and when the magnetic field is, weak, magnetic field lines are apart., 5) 3.3.2.Write the Properties of magnet, 1) A Suspended bar magnet will always point, along the north-south direction., 2) The attractive force of a magnet is maximum, near the end of the bar magnet., 3) When a magnet is broken into pieces, each, piece is a magnet., 4) Poles of a magnet have equal pole strength., 5) The ratio of magnetic length and geometrical, length is 5/6., 3.3.3 Compute the torque experienced by a magnetic, needle in a uniform magnetic field., Consider a magnet of length 2l and pole, ⃗⃗ .Force, strength 𝐪𝐦 kept in a uniform magnetic field 𝑩, experienced by each pole is, , Net force exerted on the, magnet is zero. and there, is no translatory motion., two equal and opposite, ⃗⃗⃗⃗𝑺 make a, forces ⃗⃗⃗⃗⃗, 𝑭𝑵 , 𝑭, couple about O., moment of couple tend to rotate and align the, , ⃗⃗ ., magnet in the direction of the magnetic field 𝑩, moment of force or torque 𝜏 about point O, , 3.3.4 Give an account of magnetic Lorentz force., When an electric charge q is moving with, velocity v, ⃗ in the magnetic field ⃗B, it experiences a, force, called magnetic Lorentz force ⃗⃗⃗⃗, 𝐹𝑚 ., , 1) Force is directly proportional to the magnetic, ⃗., field 𝐁, 2) Force is directly proportional to the velocity 𝐯⃗ of, the moving charge, 3) Force is directly proportional to sine of the angle, between the velocity and magnetic field, 4) Force is directly proportional to the charge q, 5) The direction of Force ⃗⃗⃗⃗⃗, 𝐅𝐦, is always, ⃗, ⃗, perpendicular to 𝐯⃗ and 𝐁, 6) The direction of Force on negative charge is, opposite to the direction of force on positive, charge, 7) If the charge q is moving along magnetic field, then, force is zero, 3.3.5 How is a galvanometer converted into an, ammeter?, A galvanometer is converted into an, ammeter by connecting a low resistance in parallel, with the galvanometer. This low resistance connected, in parallel is called shunt resistance S, Let I be the current passing through the, ammeter. Let Ig be the current passing through the, galvanometer of resistance Rg and the remaining, current (I – Ig) through shunt resistance S., , 1) An ammeter is a low resistance instrument and it, is always connected in series to the circuit, 2) An ideal ammeter has zero resistance, 3) To increase the range of an ammeter n times,, , 3.Magnetism and Magnetic Effects of Current S.Jayachandran, GHSS,Manali,Thiruvallur Dt,, , 9840430109, , Page | 11

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3.3.6 How is a galvanometer converted into an, voltmeter?, A galvanometer is converted into a voltmeter, by connecting high resistance Rh in series with, galvanometer., Let Rg be the resistance of galvanometer and Ig be the, current with which the galvanometer produces full, scale deflection. Current in the electrical circuit is, same as the current passing through the, galvanometer., , 1) Voltmeter is a high resistance instrument and it, is always connected in parallel with the circuit, 2) An ideal voltmeter has infinite resistance, 3) In order to increase the range of voltmeter n times,, , 3.5.1Find the magnetic induction due to a long straight, conductor using Biot- savart law, Let YY’ be an infinitely long, straight conductor and I be the steady current, through the conductor . P is a Point and at a, distance a from the wire. A small length AB=dl is, considered as current element I.dl at a distance r from, point P. perpendicular AC is drawn to the line BP. Let, ф be the angle between AP and OP and dф be the angle, between AP and BP., , 3.5.2 Obtain a relation for the magnetic field at a point, along the axis of a circular coil carrying current., R is the radius of a current carrying circular, loop and I is the current flowing through the wire ., P is a point on the axis of the circular coil at a, distance z from the centre of the coil O. Two, diametrically opposite current line elements of the coil, ⃗⃗⃗ are taken at C and D., each of length 𝑑𝑙, , Magnetic field at P due to current element at C, is along PR and due to current element D is along PS., Horizontal components dBcosϕ cancel out. while the, vertical components dBsinϕ alone contribute to the, ⃗ at the point P., net magnetic field ⃗𝑩, , 3.Magnetism and Magnetic Effects of Current S.Jayachandran, GHSS,Manali,Thiruvallur Dt,, , 9840430109, , Page | 12

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3.5.3 Calculate the magnetic induction at a point on, the axial line of a bar magnet., qm is the pole strength and 2l is the magnetic, length of a bar magnet NS. C is a point at a distance, r from centre of magnet on the axial line. pm = qm .2l, is the magnetic moment of magnet., , 3.5. 5 Derive the expression for the force on a currentcarrying conductor in a magnetic field, dl is the length of small element of conductor placed, in magnetic field B, with cross-sectional area A., , 3.5.4 Obtain the magnetic induction at a point on the, equatorial line of a bar magnet., qm is the pole strength and 2l is the magnetic, length of a bar magnet NS. C is a point at a distance, r from centre of magnet on the equatorial line., pm = qm .2l is the magnetic moment., , The free electrons drift opposite to the direction of, current I. relation between current I and drift velocity, 𝐯⃗⃗⃗⃗𝒅 is, , 3.Magnetism and Magnetic Effects of Current S.Jayachandran, GHSS,Manali,Thiruvallur Dt,, , 9840430109, , Page | 13

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3.5.6 Discuss the working of cyclotron in detail., Cyclotron is a device used to accelerate the, charged particles to gain large kinetic energy., Principle, When a charged particle moves, perpendicular to the magnetic field, it experiences, magnetic Lorentz force, Construction, 1) The particles are allowed to move in between two, semi-circular metal containers called Dees., 2) Dees are enclosed in an evacuated chamber where, uniform normal magnetic field acts to the plane, of the Dees., 3) The source S (the particle to be accelerated) is, placed at the centre in the gap between the Dees., 4) Dees are connected to high frequency, alternating potential difference., , The kinetic energy of the ion, , Working, 1. Positively charged ion ejected from source S, is, accelerated towards Dee-1 which has negative, potential at that time., 2. Ion moves in circular path due to Lorentz force., 3. After one semi-circular path inside Dee-1, the ion, reaches the gap between Dees., 4. At this time, the polarities of the Dees are, reversed, 5. Ion is now accelerated towards Dee-2 with a, greater velocity., 6. For this circular motion, the centripetal force on, the charged particle q is provided by Lorentz, force. Deflector plates is used for changing, direction of ion and hitting the target by ion, 7. frequency of circulation of positive ion must be, equal to the frequency of the electrical oscillator, fosc. This is resonant condition., Limitations, 1) the speed of the ion is limited, 2) electron cannot be accelerated, 3) uncharged particles cannot be accelerated, , 3.5.7 Derive an expression for Magnetic field due to a, long current carrying solenoid, Consider a solenoid of length L having N turns., , Applying Ampère’s, rectangular loop abcd, , circuital law, , for, , the, , 3.5.8 Derive the expression for the torque on a currentcarrying coil in a magnetic field., Consider a rectangular loop PQRS carrying, ⃗⃗ . Let, current I is placed in a uniform magnetic field𝑩, a and b be the length and breadth of rectangular, loop respectively., The unit vector 𝑛̂ normal to the plane of the, loop makes an angle θ with the magnetic field, , Forces 𝑭𝑸𝑹 and𝑭𝑺𝑷 are equal, opposite and collinear., , 3.Magnetism and Magnetic Effects of Current S.Jayachandran, GHSS,Manali,Thiruvallur Dt,, , 9840430109, , Page | 14

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they cancel each other. Forces 𝑭𝑷𝑸 and 𝑭𝑹𝑺 are equal, in magnitude and opposite in direction but not, collinear. 𝑭𝑷𝑸 and 𝑭𝑹𝑺 constitute a couple which, exerts a torque τ on the loop., , 3.5.9 Derive the expression for the force between two, parallel, current-carrying conductors., , Construction: Rectangular coil PQRS made of, insulated thin copper wire is wound over a light, metallic frame. The coil is suspended freely in a radial, magnetic field produced by horse-shoe magnet., The upper end of coil is attached to phosphor bronze, strip and the lower end of the coil is connected to, phosphor bronze hair spring. By using small plane, mirror, lamp and scale, deflection of the coil is, measured. Suspension strip and the spring S are, connected to voltage terminals., Working, In the radial magnetic field, parallel sides QR and SP, experience no force. Perpendicular sides PQ and RS, experience equal forces in opposite directions. Due, to this, torque is produced, , A and B are two long, straight parallel conductors, separated by a distance r, kept in air medium., I1 and I2 are the currents, passing through, A and B in same direction, (along z - direction)., By thumb rule, , G is called galvanometer constant or current reduction, factor of the galvanometer ., 3.5.11 Derive the expression for the Magnetic dipole, moment of revolving electron, The circulating electron around the nucleus, in a loop is like current in a circular loop. current I, due to circular motion of the electron is, , −e is the charge of an electron. R is the radius, of the circular orbit and v is the velocity of the electron, T is the time period of revolution of an electron and A, is the area of loop., The magnetic dipole moment 𝝁𝑳 due to current, carrying circular loop is, 3.5.10 Explain the principle and working of Moving, coil galvanometer, Moving coil galvanometer is a device used to detect, the flow of current in an electrical circuit., Principle: When a current carrying loop is placed in, a uniform magnetic field, it experiences a torque, , angular momentum L of the electron about O is, , 3.Magnetism and Magnetic Effects of Current S.Jayachandran, GHSS,Manali,Thiruvallur Dt,, , 9840430109, , Page | 15

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magnetic field, the path of the particle is not a circle, it is helix around B., 3.3.9 Find the magnetic field due to a long straight, conductor using Ampere’s circuital law., I is the current flowing in a straight, conductor of infinite length. An amperian loop in, the form of a circular shape is taken at a distance r, from the centre of the conductor., By Ampere’s circuital law, , minimum value of magnetic moment of electron when, n = 1is called bohr magneton., 3.3.7 Explain the concept of velocity selector, By using proper electric and magnetic fields,, charges moving with particular speed can be, selected in an arrangement called velocity selector., Electric field 𝐸⃗ acts between two parallel plates., uniform magnetic field ⃗⃗⃗𝐵 acts perpendicular to the, direction of electric field 𝐸⃗.Net force on charge q, entering with velocity v is, 3.3.10.Compare the properties Of Dia, Para and ferro, Magnetic materials, , Charges having this velocity v are selected to come out., 3.3.8 Discuss the motion of charged particle in, magnetic field., Consider a charged particle of charge q, ⃗⃗, having mass m entering uniform magnetic field 𝑩, with velocity 𝐯⃗. velocity v, ⃗ is perpendicular to the, ⃗, magnetic field 𝐵 . Lorentz force 𝐹 acts on the charge, ⃗ and velocity v, perpendicular to both magnetic field 𝐵, ⃗., charged particle moves in a circular orbit of radius r., ⃗⃗ = 𝒒 (𝐯⃗ 𝑿 𝑩, ⃗⃗ ), 𝑭, , 3.2.27 Why is the path of a charged particle not a circle, when its velocity is not perpendicular to the magnetic, field?, Resolving particle velocity with respect to, magnetic field, the parallel component of velocity, vCosѲ remains unchanged and drags the charge, along magnetic field. The perpendicular component, of velocity vSinѲ keeps changing in direction due to, Lorentz force and makes the charge to rotate., Hence the path of the particle is not a circle; it is a, helical around the magnetic field., 3.2.22 state curie’s law, , magnetic susceptibility of a material, decreases with increase in temperature., If a charged particle moves in magnetic field, such that its velocity is not perpendicular to the, 3.Magnetism and Magnetic Effects of Current S.Jayachandran, GHSS,Manali,Thiruvallur Dt,, , 9840430109, , Page | 16

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4 ELECTROMAGNETIC INDUCTION, AND ALTERNATING CURRENT, 4.2.1 State Lenz’s law., Direction of the induced current will oppose, the cause that produces it., 4.2.2 State Fleming’s right hand rule., The thumb, index finger and middle finger of right hand, are in mutually perpendicular directions., If the index finger points the direction of the, magnetic field and the thumb points the direction of, motion of the conductor, then the middle finger will, point the direction of the induced current., 4.2.3 Mention the ways of producing induced emf., 1) By changing the magnetic field B, 2) By changing the area A of the coil and, 3) By changing the orientation θ of the coil with, magnetic field, 4.2.4List out the advantages of stationary armaturerotating field system of AC generator., 1) Current flows directly from the stator without, the use of contact brushes., 2) Easy to Insulate armature winding., 3) Number of slip rings is reduced., 4) Armature windings can be built strongly to, prevent damage., 4.2.5How will you define RMS value of an alternating, current?, The root mean square value of an alternating, current is defined as the square root of the mean of, the squares of all currents over one cycle., , 4.2.6How will you define Q-factor?, Ratio of voltage across L or C to the applied voltage, is called Quality or Q-factor, , 4.2.7 What is meant by wattles current?, If the power consumed by current in an AC, circuit is zero then that current is called wattles current, 4.2.8 What do you mean by resonant frequency?, The frequency at which resonance takes place, so that impedance is minimum and current is, maximum is called resonant frequency., 4.2.9 What are the Advantages of AC over DC, 1) AC can be produced cheaper than DC., 2) AC transmission loss is small compared to DC, transmission., 3) AC can easily be converted into DC with the help, of rectifier, 4.2.10 Give the Application of eddy currents, 1.Induction stove, 2.Eddy current brake, 3.Eddy current testing 4.Electromagnetic damping, 4.Electromagnetic Induction, , 4.2.11 What are the disadvantages of AC over DC, 1) Alternating voltages cannot be used for charging, of batteries, electroplating, electric traction etc., 2) At high voltages, AC is more dangerous to work, than DC., 4.2.12 What are phasors?, A rotating vector which rotates about the, origin in anti-clockwise direction at a constant, angular velocity ω to represent a sinusoidal, alternating voltage is called Phasor., 4.2.13 What is meant by electromagnetic induction?, Whenever the magnetic flux linked with a, closed circuit changes, an emf is induced in the, circuit., 4.2.14 State Faraday’s laws of electromagnetic, induction., First law : Whenever magnetic flux linked with a, closed circuit changes, an emf is induced in the, circuit., Second law: The magnitude of induced emf is equal, to the rate of change of magnetic flux., 4.2.15.How is Eddy current produced?, How do they flow in a conductor?, When magnetic flux linked with a metal sheet, or plate changes, current is induced, known as Eddy, currents. Eddy or Foucault currents flow in, concentric circular paths., 4.2.16What for an inductor is used with some examples, Inductor is a device used to store energy in a, magnetic field when an electric current flows, through it. Example: Coils, Solenoids and Toroids., 4.2.17What do you mean by self-induction?, When current flowing in a coil is changed ,an, emf is induced in that same coil., 4.2.18What is meant by mutual induction?, When current flowing in a coil is changed ,an, emf is induced in other near coil., 4.2.19 What are step-up and step-down transformers?, Step-up transformer converts low alternating, voltage into high alternating voltage., Step-down, transformer, converts, high, alternating voltage into low alternating voltage., 4.2.20 Define average value of an alternating current., Average of the positive current values, or, negative current values is called average value of an, alternating current., 4.2.21Define electric resonance., When the frequency of the applied alternating source, is equal to the natural frequency of the RLC circuit,, the current is maximum.The circuit is in electrical, resonance and frequency is resonant frequency., 4.2.22 Give any one definition of power factor., Power factor = cos ϕ = cosine of the angle of lead or, lag between current and resultant voltage., , S.Jayachandran, PG.Asst,GHSS,Manali,Thiruvallur Dt,, , 9840430109 Page 17

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4.2.23What are LC oscillations?, Oscillations of energy in a pure LC circuit,, between the magnetic energy of the inductor and the, electrical energy of the capacitor of definite, frequency are called are called LC oscillations., 4.2.24Define Self Inductance, Self-inductance of a coil is defined as the flux, linkage with coil when one Ampere current flows in, the coil. Unit: henry, 4.2.25Define Mutual Inductance, Mutual inductance M21 is defined as the flux, linkage with coil 2 when one Ampere current flows, in coil 1. Unit: henry., 4.2.26How will you define the unit of inductance?, Henry is the inductance of a coil when one, Ampere current flowing in coil produces unit flux, linkage in the same coil., 4.2.27 What do you understand by self-inductance of a, coil? Give its physical significance., Self-Inductance of a coil opposes the change, in current flowing in it and tries to maintain the, original current. Inductance in a circuit plays the role, of inertia and moment of inertia in mechanical motion., 4.3.1 Mention the various energy losses in a, transformer., Flux leakage: Energy is lost when the magnetic lines, of primary coil are not completely linked with, secondary coil. This flux leakage is minimized by, winding coils one over the other., Copper loss :Energy is lost due to Joule heating,, when an electric current flows through Transformer, windings, This copper loss is minimized by using thick, wires., Core loss or Iron loss:, 1)Energy is lost in the form of heat, when, transformer core is magnetized and demagnetized, repeatedly by the alternating voltage. Hysteresis loss is, minimized by making transformer core using silicon, steel., 2)Energy is lost in the form of heat, when eddy, currents are induced due to Alternating magnetic, flux in the core. Eddy current loss is minimized by, using laminated transformer core., 4.3.2. How much energy is stored in an inductor of, inductance L while establishing the current in it?, Whenever current is changing in the inductor, circuit, the inductance opposes the change in current., work is done by some external agency to change the, current. This work done is stored as magnetic potential, energy., , 4.Electromagnetic Induction, , 4.3.2.Derive an equation for Self inductance of a solenoid, , l is the length, A is the cross-sectional area and n is, the number of turns per unit length of the solenoid., When current i passes through the solenoid,, magnetic field is produced in the solenoid., , Inductance depends on the geometry of the solenoid and, the medium present inside the solenoid., 4.3.3.Derive an equation for Mutual inductance between, two long co-axial solenoids, l is the length, A1,A2 is the cross-sectional, area and n1,n2 is the number of turns per unit length, of the two long solenoids 1 and 2. When i1 current, passes through the solenoid 1,a magnetic field 𝑩𝟏 is, produced in it., , S.Jayachandran, PG.Asst,GHSS,Manali,Thiruvallur Dt,, , 9840430109 Page 18

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4.3.4.Obtain an expression for motional emf from, Lorentz force., A conductor rod AB of length l moves right, with a velocity v in a magnetic field B acting, By Kirchoff’s loop rule the algebraic sum of potential, perpendicular inwards. Free electrons inside the rod, differences in a closed circuit is zero., experiences downward Lorentz force and gets collected, at end A of the rod., Collection of free electrons at end A produces, Electric field E. electric field exerts upward coulomb, force and stops further collection of free electrons at, end A. So, Potential difference is induced across the, ends of the rod., , applied voltage and the current, are in phase in a resistive circuit, Comparing the electromagnetic oscillations of LC, circuit with mechanical oscillations of spring find, This emf expression for angular frequency of LC oscillator., produced due to the movement of the rod, is known as, motional emf., , 4.3.5.*How will you induce an emf by changing the area, enclosed by the coil?, Metal rod of length l moves left with a velocity, v on a rectangular metal frame. Metal frame is placed, in a normal magnetic field., As the rod moves from AB to DC in a time dt, the, area and the magnetic flux through the loop, decreases. So, an emf is induced in the loop., Derive an expression for RMS value of AC, The root mean square value of an alternating, current is defined as the square root of the mean of, the squares of all currents over one cycle. Alternating, current is given by 𝒊 = 𝒊𝒎 𝑺𝒊𝒏𝝎𝒕, , Due to motional emf, direction of induced current is, clockwise given by Fleming’s right hand rule., 4.3.6 Find out the phase relationship between voltage, and current in a pure resistive circuit., A pure resistor of resistance R is connected across an, alternating voltage source., 4.Electromagnetic Induction, , S.Jayachandran, PG.Asst,GHSS,Manali,Thiruvallur Dt,, , 9840430109 Page 19

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4.5.1Show mathematically that the rotation of a coil in, a magnetic field induces an alternating emf., A Rectangular coil of N turns is rotated with a, angular velocity ω in magnetic field B about an axis, perpendicular to B., When t =0 plane of coil is perpendicular to B, magnetic, flux is maximum., , perpendicular to the plane of the loop PQRS. The, induced emf between P and S is zero.(point O), When field magnet rotates through 90°,the magnetic, field is parallel to the plane of the loop PQRS. The, induced emf between P and S is maximum. By using, Fleming’s right hand rule, induced current flows, along PQRS. (point A), When plane of coil is inclined to B at an angle Ѳ, When field magnet rotates through 180°,the magnetic, field is again perpendicular to PQRS and the, magnetic flux linkage is, induced emf between P and S is zero. (point B), When field magnet rotates through 270°,the magnetic, field is again parallel to the plane of the loop PQRS., The induced emf between P and S is maximum but, reversed. By using Fleming’s right hand rule ,induced, current flows along SRQP.(point C), When field magnet completes 360°,the induced emf, becomes zero. (point D), when field magnet completes one rotation, induced, emf in PQRS finishes one cycle. emf induced in, PQRS is alternating in nature., 4.5.3.Explain the construction and working of transformer., Transformer is a stationary device used to, transform electrical power from one circuit to, Induced, another without changing its frequency, Emf, Principle : Mutual induction between two coils., by, Construction:Two insulated coils are wound over, faraday law, laminated core of silicon steel. core and coils are kept, in a container filled with suitable medium for better, insulation and cooling purpose., Working: When alternating voltage is fed to primary, coil P, an alternating magnetic flux is set up in the, laminated core. So, emf is induced in both primary, and secondary coils S. For both primary and, As the induced emf varies as sine function of the time secondary coils, rate of change of magnetic flux per, angle ωt, it is called sinusoidal emf or alternating emf. each turn is same., 4.5.2Explain the working of a single-phase AC, generator with necessary diagram., In a single phase AC generator, a single, armature generates a single-phase alternating emf., Principle :Electromagnetic Induction, Stator: Rectangular conducting loop PQRS., Rotor: 2 salient electromagnetic poles., , 𝜺𝑷 , 𝑽𝑷 , 𝑵𝑷 are the induced emf, applied ac Voltage, and number of turns of the primary coil respectively., 𝜺𝑺 , 𝑽𝑺 , 𝑵𝑺 are the induced emf, drawn ac Voltage and, number of turns of the Secondary coil respectively., For Step up transformer K>1, 𝑵𝑺 >𝑵𝑷 , 𝑽𝑺 >𝑽𝑷 , 𝑰𝑺 < 𝑰𝑷, voltage is increased but current is decreased., Step down transformer K<1, 𝑵𝑺 < 𝑵𝑷 ,𝑽𝑺 < 𝑽𝑷 , 𝑰𝑺 > 𝑰𝑷, voltage is decreased but current is increased., WorkingThe loop PQRS is stationary. Field magnet is Ratio of the useful output power to the input power, rotated in clockwise direction.Initially magnetic field is is known as Efficiency of a transformer., 4.Electromagnetic Induction, , S.Jayachandran, PG.Asst,GHSS,Manali,Thiruvallur Dt,, , 9840430109 Page 20

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4.5.4 Derive an expression for phase angle between the, applied voltage and current in a series RLC circuit., A resistor of resistance R, a inductor of, inductance L and a capacitor of capacitance C are, connected in series across an alternating voltage., 𝐯 = 𝑽𝒎 𝑺𝒊𝒏𝝎𝒕, , The quantity ωL acts as resistance called inductive, reactance (X L) in inductive circuit. unit: ohm., net voltage drop across L-C combination is VL – VC For Direct current, f = 0. ⸫ XL = 0. Thus an ideal, which is represented by a phasor OD., inductor offers no resistance to steady DC current., By parallelogram law, the diagonal OE gives the 4.5.6Find out the phase relationship between voltage, resultant voltage V of VR and (VL – VC), and current in a pure capacitive circuit., A capacitor of capacitance C is connected, across an alternating voltage source., , If XL > X C, (X L−XC) is positive and phase angle ϕ is, positive., ,, If XL < X C, (X L−XC) is negative and phase angle ϕ is, negative., ,, If XL < X C, (X L−XC) is zero phase angle ϕ is zero., 4.5.5 Find out the phase relationship between voltage, and current in a pure inductive circuit., A pure inductor of inductance L is connected, across an alternating voltage source., , 4.Electromagnetic Induction, , S.Jayachandran, PG.Asst,GHSS,Manali,Thiruvallur Dt,, , 9840430109 Page 21

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The quantity 1/Cω acts as resistance and is called 2) Circular metal disc connected to the wheel, capacitive reactance (X C) in capacitive circuit. unit:, rotates in between the poles of an electromagnet., ohm. For Direct current, f = 0. ⸫ XC = ∞. So, an 3) When there is a relative motion between the disc and, the magnet, eddy currents are induced in the disc, ideal capacitor blocks steady DC current., which stop the train., 4.5.7 Obtain an expression for average power of AC, Eddy current testing, over a cycle. Discuss its special cases., Power is given by the product of the voltage and 1) Eddy current testing methods is used to find, defects like surface cracks, air bubbles present in, current. In an AC circuit, the voltage and current vary, a specimen., continuously with time. So, power at an instant is, calculated and then it is averaged over a complete cycle. 2) alternating electric current passing in a coil, produces an alternating magnetic field., 3) When this coil is brought near the test surface, eddy, current is induced in the test surface. change in, phase and amplitude of the eddy current, confirms presence of defects., Electro magnetic damping, 1) The armature of the galvanometer coil is wound on, a soft iron cylinder., 2) when the coil moves the radial magnetic field, induces eddy current in the cylinder., 3) Damping force of eddy current brings the, armature to rest immediately. and then, galvanometer shows a steady deflection. This is, called electromagnetic damping., 𝑽𝑹𝑴𝑺 𝑰𝑹𝑴𝑺 is called apparent power and cos ϕ is 4.5.9 Show that the total energy is conserved during LC, oscillations., power factor. The average power of an AC circuit is, In LC oscillations , energy U oscillates between, known as true power of the circuit., electric energy 𝑼𝑬 of a capacitor and magnetic energy, 𝑼𝑩 of a inductor., Magnetic and electric energy vary with time, but the, total energy remains constant ., Case(i) When stored charge is maximum in capacitor, q=𝑸𝒎 and current i is zero in inductor. Total energy, is fully electrical energy, , 4.5.8 Give the uses of Foucault current, when magnetic flux linked with a conductor, in, the form of a sheet or plate, an emf is induced. induced, currents flow in concentric circular paths known as, Eddy currents or Foucault currents., Induction stove, 1) When the stove is switched on, an alternating, current flowing in the tightly wound coil of, insulated wire produces high frequency, alternating magnetic field., 2) alternating magnetic field induces very strong, eddy currents in the cooking pan of suitable, material., 3) The eddy currents in the pan produce large heat, due to Joule heating which cooks the food., Eddy current brake, 1) Eddy current braking system is used in high, speed trains and roller coasters, 4.Electromagnetic Induction, , Case(ii)When stored charge is zero in capacitor q=0, and current is maximum i=𝑰𝒎 in inductor., , Total energy is fully, magnetic energy, Case(iii)When stored charge is q in capacitor and, current is i in inductor., , By conservation of energy, total energy of the system, remains constant., , S.Jayachandran, PG.Asst,GHSS,Manali,Thiruvallur Dt,, , 9840430109 Page 22

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5 ELECTROMAGNETIC WAVES, , 5.2.9 How are gamma rays produced and give its uses, , 5.2.1.What is displacement current?, Current produced in the region where the electric, field and the electric flux are changing with time is, known as displacement current., 5.2.2.What is meant by Fraunhofer lines?, Dark lines in the solar spectrum are known as, Fraunhofer lines. By comparing absorption spectra, for various materials, Fraunhofer lines helps in, identifying elements present in the Sun’s atmosphere, 5.2.3 How are radiowave produced and give its uses, , 5.2.4 How are microwave produced and give its uses, , 5.2.5 How are infrared waves produced and give its uses, , 5.2.6 How are visible light produced and give its uses, , 5.2.7 How is UV light produced and give its uses, , 5.2.8 How are X-rays produced and give its uses, , 5.2.10 Why are e.m. waves non-mechanical, Electromagnetic waves do not require medium to, travel. But mechanical waves require medium to travel., So, e.m. waves are non-mechanical., 5.3.1Write down the properties of electromagnetic, waves., 1) Electromagnetic waves are produced by, accelerated charge., 2) Electromagnetic waves do not need any medium, for propagation.So,they are non-mechanical waves, 3) Electromagnetic waves are transverse in nature., 4) Electromagnetic waves travel with the speed of, light in vacuum., 5) speed of electromagnetic wave v in any medium is, less than speed in vacuum c . v < 𝑐, 6) Electromagnetic waves are not deflected by electric, field or magnetic field., 7) Electromagnetic waves can show interference,, diffraction and polarisation., 8) Electromagnetic waves carries energy, momentum, and angular momentum., 5.5.1What is emission spectra?Give their types., Emission spectra, Spectrum obtained from self luminous source, directly is called emission spectrum. Each source has, its own characteristic emission spectrum., Emission spectra is classified into 3 types, 1.Continuous emission spectra, Contains wavelengths of all visible colours from, violet to red.Spectrum obtained from carbon arc,, incandescent solids are continuous spectra., 2.Line emission spectrum, Contains sharp lines of definite wavelengths. Such, spectra arise when atoms of elements are excited., Reveals the characters of the element. Different for, different elements. Spectrum of atomic hydrogen,, helium., 3.Band emission spectrum, Contains closely spaced overlapping spectral lines, forming bands and separated by dark spaces.Such, spectra arise when the molecules are excited, spectrum has a sharp edge at one end and fades out at, the other end.Band spectrum is the characteristic of the, molecule hence, the structure of the molecules can be, studied using their band spectra., Spectra of ammonia gas in the discharge tube etc., , 5.Electromagnetic waves S.Jayachandran, PG.Asst, GHSS, Manali,Thiruvallur Dt. 9840430109, , Page 23

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5.5.2. What is absorption spectra?. Give their types., Absorption spectra, Spectrum obtained from light, after passing through, a medium or an absorbing substance is called, absorption spectrum. Each substance has its own, characteristic emission spectrum., Absorption spectra is classified into 3 types, Continuous absorption spectrum, When white light passes through a blue glass plate, it, absorbs all colours except blue. This is an example of, continuous absorption spectrum., Line absorption spectrum, When white light from carbon arc, passes through, sodium vapour, sodium absorbs only two yellow, wavelength. Continuous spectrum with two dark lines, in the yellow region of sodium vapour is obtained., Band absorption spectrum, when white light is passed through the iodine vapour,, or through diluted solution of blood or through, chlorophyll or through solutions of organic and, inorganic compounds, dark bands on continuous, bright background is obtained., 5.5.3Write down Maxwell equations in integral form., I.First equation is Gauss’s law for electricity., Surface integral of electric field over a closed surface, 𝟏, is equal to times the net charge inside the surface., 𝜺𝟎, , electric field lines do not form a continuous closed, path. isolated positive charge or negative charge can, exist. It relates the net electric flux to net electric charge, enclosed in a surface., II. Second equation is Gauss’s law for magnetism, Surface integral of magnetic field over a closed, surface is zero., magnetic lines of force form a continuous closed, path. isolated magnetic monopole do not exists., III.Third equation is Faraday’s law of electromagnetic, induction., Line integral of the electric field is equal to, the rate of change of magnetic flux around any, closed path., III.Fourth equation is Ampere – Maxwell’s law, Magnetic field around any closed path is, related to the conduction current and displacement, current through that path., , 5.Electromagnetic waves S.Jayachandran, PG.Asst, GHSS, Manali,Thiruvallur Dt. 9840430109, , Page 24

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6.2.10.State the laws of refraction., 1) Incident ray, Refracted ray and Normal are, Coplanar., 6.2.1 What are the two conditions for total internal, 2) The ratio of sine of angle of incidence sin i in the, reflection ?, first medium to the sine of angle of refraction, 1) light must travel from denser to rarer medium,, sin r r in the second medium is equal to the ratio, 2) angle of incidence in the denser medium must be, of refractive index of the second medium n2 to that, greater than critical angle (i > ic)., of the refractive index of the first medium n1, 6.2.2Explain the reason for glittering of diamond., Refractive index of diamond is about 2.417,, greater than the refractive index of ordinary glass. The 6.2.11 State the laws of reflection., ray, Reflected ray and Normal are, critical angle of diamond is 24.4°. So the angle of 1.Incident, coplanar., several cut faces can be from 24.4°to 90°.So light 2.The angle of incidence i is equal to the angle of, entering the diamond is total internally reflected, reflection r., from the several cut faces before getting out. So 6.2.12 What is mirage?, diamond glitters., Optical illusioned image of the object formed, 6.2.3Why does sky appear blue?, down on hot area, by the upward bending of light, By Rayleigh’s scattering law, intensity of light rays due to different refractive index of air layers, scattered is inversely proportional to fourth power on hot region is called Mirage., of wavelength. violet colour which has the shortest 6.2.13 What is looming?, Optical illusioned image of the object formed, wavelength gets much scattered during day time. As, up, on, hot, area, by the downward bending of light, our eyes are more sensitive to next scattered blue, colour than violet colour the sky appears blue during rays due to different refractive index of air layers on, cold regions is called Looming., day time, 6.2.4What is the reason for reddish appearance of sky 6.2.14 What is Rayleigh’s scattering?, Intensity of light in Rayleigh’s scattering is, during sunset and sunrise?, During sunrise and sunset, the light from sun inversely proportional to fourth power of, travels a greater distance. By Rayleigh’s scattering, wavelength., violet colour which has the shortest wavelength gets 6.2.15What is optical path?, Optical path is the distance d' travelled by, much scattered away and the red light of longer, wavelength reaches our eye. This is the reason for the light in vacuum for the same time as it travels a, distance d in the medium., reddish appearance of sky during sunrise and sunset., 6.2.16What is Snell’s window?, 6.2.5Why do clouds appear white?, The restricted illuminated circular area, Clouds contains large amount of dust and, water droplets, which have size a greater than the formed by refraction of light entering water is, wavelength λ of light. In clouds all the colour’s get called Snell’s window., equally scattered not depending on wavelength. So 6.2.17 What is critical angle and total internal, reflection?, clouds appear white., The angle of incidence in the denser medium, 6.2.6 Why sky appears dark for the astronauts, for, which, the refracted ray graces the boundary is, Above the atmosphere, there is no light, scattering particles. So sky appears dark for the called critical angle ic., Complete reflection of light into the denser, astronauts, medium, itself, is called total internal reflection, 6.2.7 How are rainbows formed?, , 6.2.18 What is power of a lens?, Power of a lens is a measure of the degree, of, convergence, (or) divergence the lens produces, 6.2.7 Why do stars twinkle?, Stars appear twinkling because of the refraction of on the light falling on it. The power of a lens P is, light by movement of the atmospheric layers with equal the reciprocal of its focal length., Rainbow is formed due to dispersion of sunlight, through droplets of water during rainy days., , varying refractive indices, which is clearly seen in the, night sky., 6.2.8 What is principle of reversibility?, Light will travel the same path if its direction, of travel is reversed., 6.2.9 What is dispersion?, Dispersion is splitting of white light into its, constituent colours., 6. Ray Optics, , 6.2.19 Give the characteristics of image formed by a, plane mirror., 1) The image formed by a plane mirror is virtual,, erect, and laterally inverted., 2) The size of the image and object are same., 3) The distance of object and image from the mirror, are same., , S.Jayachandran, PG.Asst,GHSS,Manali,Thiruvallur Dt,, , 9840430109, , Page 25

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6.2.20 How does an endoscope work?, An endoscope is an instrument which has bundle of, optical fibres working on the principle of total, internal reflection. It is used by doctors to see inside, of a patient’s body and do operations. The optical, fibres are inserted into the body through mouth, nose, (or) a special hole made in the body., 6.3.1. What are the Cartesian sign conventions for a, spherical mirror? Diagram not necessary, 6.3.4. Obtain the equation for critical angle., When light passes from an optically denser, 1) The Incident light, medium, to an optically rarer medium, it bends away, travels from, from the normal. As angle of incidence i is increased,, left to right, angle of refraction r increases and at a certain stage r, becomes 90°. The angle of incidence in the denser, (i.e.,Object must be placed on left side of mirror)., 2) All the distances are measured from the pole P of medium for which the refracted ray graces the, boundary is called critical angle ic., the mirror., 3) Right side distances to the pole are taken as By Snell’s law, positive., 4) Left side distances to the pole are taken as, negative., 5) Upward perpendicular Heights are taken as, positive., 6) Downward perpendicular Heights are taken as, negative., 6.3.2 Derive the relation between f and R for a spherical, mirror., 1) C is the centre of curvature of the mirror with pole, P. PF= f is focal length and PC =R is the radius, of curvature., 6.3.5 Obtain the equation for apparent depth., 2) A ray of light passing parallel to the principal, Bottom of a tank filled with water appears to, axis is incident at M., be raised when seen from top air medium., 3) After reflection, it passes through the principal, Light from the object O passes from denser, focus F., medium (water) to rarer medium (air) to reach our, 4) CM is drawn normal to the mirror and MP is the eyes. The refractive index of the denser medium is n1, drawn perpendicular to the principal axis., and that of rarer medium is n2. The angle of incidence, in the denser medium is i and the angle of refraction in, the rarer medium is r. By Snell’s law, , 6.3.3 What is optical path? Obtain its equation., Distance d' travelled by light in vacuum in, the same time as it travelled a distance d in a, medium is known as Optical path of the medium., Light travels with a speed v through a medium, of refractive index n and distance d in a time t. Light, travels with a speed c through vacuum and distance d', in the same time t., 6. Ray Optics, , S.Jayachandran, PG.Asst,GHSS,Manali,Thiruvallur Dt,, , 9840430109, , Page 26

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6.3.6 Derive the equation for effective focal length for, lenses in contact., Two lenses of focal length f 1 and f2 are placed, coaxially in contact with each other. When Object O is, placed beyond Focus of first lens ,an image is formed, by it at I'. This image I' acts as an object for the, second lens. and the final image is formed at I by, Second Lens., For First Lens, object distance 𝐏𝑶 = 𝒖 and image, distance 𝐏𝐈 ′ = 𝐯 ′ .For Second Lens, object distance, 𝐏𝐈 ′ = 𝐯 ′ and image distance 𝐏𝑰 = 𝐯, , 6.5.1 Describe the Fizeau’s method to determine speed, of light., Light from source S falls on a partially, silvered glass plate G kept at an angle of 45o to the, incident light. Light then passes through one cut of, a rotating toothed-wheel with N teeth and N cuts of, equal widths., When wheel is not rotating, light travels a long, distance d, about 8 km, gets reflected from a mirror and, passes through the same cut and reach the eyes of the, observer., Working: The wheel is rotated with high angular, speed ω, until light passing through one cut would, completely be blocked by the adjacent tooth. So the, observer cannot see the image of source., Expression for speed of light:, Ɵ is the angle between one tooth and the next, slot which is turned within that time t and distance, covered by light is 2d., , 6.3.7 Obtain the equation for lateral magnification of, thin lens.., An object 𝐎𝐎′ of height h1 is placed on the, principal axis perpendicular to the principal axis. The, inverted real image 𝐈𝐈 ′ of height h2 is formed., Lateral (or) transverse magnification m is, defined as the ratio of the height of the image to, height of the object, , value of speed of light determined by Fizeau was very, close to the actual value c = 2.99792 ×108 m s–1, 6.5.2 Derive the mirror equation and the equation for, lateral magnification., First paraxial light BD from the object AB gets, reflected on the concave mirror at D and passes through, the focus F., Second light ray BP incident at the pole P is, reflected along P𝑩′ ., Third light ray BC passing through centre of, curvature C, gets reflected back along the same path., The three reflected rays intersect at the point where, a real, inverted image 𝑨′ 𝑩′ is formed., , magnification is negative for real image and positive, for virtual image. In the case of a concave lens, the, magnification is always positive and less than one., 6. Ray Optics, , S.Jayachandran, PG.Asst,GHSS,Manali,Thiruvallur Dt,, , 9840430109, , Page 27

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This equation is called the lens maker’s formula,, because it tells the lens manufactures what curvature, is needed to make a lens of desired focal length f with, a material of particular refractive index n., 6.5.4Derive the equation for angle of deviation in a, prism and refractive index of material of the prism., PQ is the incident ray QR is the refracted ray, and RS is the emergent ray. 𝒊𝟏 and 𝒓𝟏 are angles of, incidence and refraction at the first face AB. 𝒊𝟐 and 𝒓𝟐, are angles of incidence and refraction at the first face, AC. The angle between the incident ray PQ and the, This is Mirror Equation, The lateral (or) transverse magnification m is emergent ray RS is called the angle of deviation d., defined as the ratio of the height of the image to the, height of the object., 6.5.3 Obtain lens maker’s formula and mention its, significance., A thin lens of refractive index 𝒏𝟐 is placed, between two medium of same refractive index 𝒏𝟏 . Let, 𝑹𝟏 and 𝑹𝟐 be the radii of curvature of two spherical, surfaces 1 and 2 respectively., Using the ray from object O, after refraction,, Surface 1 forms image at 𝑰′ . But the image at 𝑰′ acts, as object for surface 2. So surface 2 bends the ray, and forms final Image at I., refraction at a spherical surface 1 when light moves Angle of deviation decreases with increase in angle of, from medium of refractive index 𝐧𝟏 to 𝐧𝟐 is, incidence and reaches a minimum value called angle of, minimum deviation and then continues to increase., Refracted ray inside the prism is parallel to its base, of the prism., Refraction at a spherical, surface 2 when light moves from medium of refractive, index 𝐧𝟐 to 𝐧𝟏 is, , 6.5.5 What is dispersion? Obtain the equation for, dispersive power of a medium., Dispersion is splitting of white light into its, constituent colours. A is the angle of a small angle, prism A=100 and δ be its angle of minimum deviation., Refractive index of prism, , 6. Ray Optics, , S.Jayachandran, PG.Asst,GHSS,Manali,Thiruvallur Dt,, , 9840430109, , Page 28

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Let δV, δR are the angles of deviation for violet and red, light. Let nV and nR are the refractive indices for the, violet and red light respectively., , The dispersive power ω is positive and dimensionless, quantity. It depends only on the nature of material, of the prism and not on the angle of the prism., 6.5.6 Obtain the equation for radius of illumination (or), Snell’s window, when light entering the water from outside is, seen from inside the water, the view is restricted to a, particular angle equal to the critical angle i𝒄, (48.60).The restricted illuminated circular area is, called Snell’s window. Light is seen from a point A at, a depth d., By Snell’s law, , 6.5.8 Derive the equation for refraction at single, spherical surface., 𝒏𝟏 and 𝒏𝟐 are the refractive indices of two, transparent media separated by a spherical surface., Light from O falls on the refracting surface at N. As, 𝒏𝟐 > 𝒏𝟏 , light deviates towards the normal and meets, the principal axis at I where the image is formed., , reciprocating and taking square root,, , radius R of the Snell’s window depends on the depth, d from which it is seen and also the refractive index, n of the medium., 6.5.7 Derive the equation for acceptance angle and, numerical aperture, of optical fiber., Light should be incident at a certain angle, called acceptance angle at the end of the optical fibre, while entering into it. At acceptance angle only,, critical angle incidence occurs in the core-cladding, boundary inside the optical fibre. i𝒂 is the acceptance, angle at the outer medium and core boundary at A., 6. Ray Optics, , If the first medium is air, then 𝒏𝟏 = 1 and for the, second medium 𝒏𝟐 = n,, 6.2.21 What are primary focus and secondary focus of a, lens? Primary focus F1 is a point where a light source, kept produces emergent rays parallel to the principal axis, after refraction through lens., Secondary focus F2 is a point where all the rays, travelling parallel to the principal axis, after refraction, through lens, converge to form an image on the principal, axis., , S.Jayachandran, PG.Asst,GHSS,Manali,Thiruvallur Dt,, , 9840430109, , Page 29

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7.2.1Why diffraction in sound more than light?, Wavelength of sound wave is large and, comparable to the geometry of obstacles like door,, windows and buildings. So, sounds bends through them., But wavelength of light wave is very small and not, comparable to the geometry of obstacles. So, light, will not bend through the edges of those obstacles., 7.2.2 State Brewster’s law., Tangent of the polarising angle of a, transparent medium is equal to its refractive index, 7.2.3 State Malus’ law., Transmitted Light intensity I from the, analyser is directly proportional to square of the, cosine of the angle θ between the transmission axis, of polariser and analyser., 7.2.4 What is myopia? What is its remedy?, A person suffering from nearsightedness or, myopia cannot see distant objects clearly. Wearing, concave lens is its remedy, 7.2.5 What is hypermetropia? What is its remedy?, A person suffering from farsightedness or, hypermetropia cannot clearly see near objects close to, the eye.Wearing convex lens is its remedy, 7.2.6.What is astigmatism? What is its remedy?, Astigmatic person cannot see all the directions, equally well. Wearing cylindrical lenses is its remedy, 7.2.7 What is presbyopia?, Farsightedness arising due to aging is called, presbyopia as the aged people cannot strain their eye, more to reduce the focal length of the eye lens, 7.2.8.Define Optic Axis, Inside the crystal there is a particular direction, in which both the rays travel with same velocity. This, direction is called optic axis., 7.2.9 Define wavefront, A wavefront is the locus of points which are, in the same state (or) phase of vibration., 7.2.10 State Huygens’ principle., 1. Each point on the wavefront behaves as the, source of secondary wavelets spreading in all, directions with the speed of the wave., 2. The envelope to secondary wavelets gives the, position and shape of the new wavefront at a later, time., 7.2.11 What are coherent waves?, Two waves which have same phase or constant, phase difference, same frequency or wavelength,, same waveform and preferably same amplitude., Why two independent monochromatic sources can, never be coherent, Atoms while emitting light, produce change, in phase due to thermal vibrations. So waves emitted, from two sources will be of same frequency and same, amplitude, but not with same phase, , 7.2.12What are Conditions for obtaining clear and broad, interference fringes?, 1) Distance D between the screen and double slit, should be as large as possible., 2) Wavelength λ of light used must be as long as, possible., 3) Distance d between the two slits must be as small, as possible., 7.2.13.Differentiate Fresnel and Fraunhofer diffraction., , 7.2.14.Differentiate interference and diffraction, , 7.2.15.What is Rayleigh’s criterion?, Two points on an image are said to be just, resolved when the central maximum of one, diffraction pattern coincides with the first minimum, of the other and vice-versa., 7.2.16. Differentiate resolution and magnification?, , 7.2.17. Differentiate polarised and unpolarised light., , 7.2.18What are near point and normal focusing?

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7.2.19 Why Compact Disc appear colourful?, Narrow circular tracks with widths, comparable to the wavelength of visible light are on, the read/writable shining side of CD. tracks act as, reflecting grating. Diffraction takes place after the, reflection of incident white light ., 7.2.20 What is the use of an erecting lens in a terrestrial, telescope?, To form an erect image from an inverted, image formed by objective lens., 7.2.21. Why is oil immersed objective preferred in a, microscope?, , 7.2.27.Define Diffraction?, Bending of waves around sharp edges into the, geometrically shadowed region., 7.2.28What is polarisation?, Phenomenon of restricting the electric or, magnetic vibrations of light to any one direction, perpendicular to wave propagation is called, polarisation of light, 7.2.29 What are polariser and analyser?, Polaroid which polarises the light passing, through it is called a polariser. The polaroid which, checks whether a light is polarised or not is called an, analyser., , For High magnification, minimum distance 7.3.1State and prove Brewster’s law, between the two points on the object to be Tangent of the polarising angle is equal to refractive, resolved dmin should be decreased by increasing index of a medium., At the polarising angle, the reflected and the refracted, optical path. So, objective of the microscope is, rays are perpendicular to each other., , immersed into a bath containing oil of refractive, index n., , 7.2.22. What are the advantages and disadvantages of a, reflecting telescope?, Advantages, 1) objective mirror in reflecting telescope is polished, on one surface only., 2) Entire back of the mirror can be used for, supporting but in lens only rim can be used., 3) Mirror weight is less than lens., Disadvantages, Objective mirror focus the light inside the, telescope tube., 7.2.23.What are the salient features of corpuscular, theory of light?, 1. light is emitted as tiny, massless and perfectly, elastic particles called corpuscles., 2. reflection of light is due to the repulsion and, refraction of light is due to the attraction of the, corpuscles by the medium., 3. energy of light is the kinetic energy of corpuscles, 4. sizes of the corpuscles give different colours to light, 7.2.24.What are the salient features of wave theory of, light?, 1. light is a disturbance from a source which travels, as longitudinal mechanical waves through the, ether medium., 2. wave theory could successfully explain reflection,, refraction, interference and diffraction of light, , 7.3. 2Explain the construction and working Nicol prism, , Nicol prism produces polarized light by, Double refraction., , The two halves are joined by a transparent cement, Canada balsam. When Unpolarised light is incident on, the Nicol prism, Double refraction takes place and, the ray is split into ordinary and extraordinary rays., The ordinary ray is total internally reflected at the, Canada balsam layer and is stopped coming from the, opposite face. The extraordinary ray which is plane, polarized, is transmitted through the crystal., 7.2.25 Define Polarising angle, The angle of incidence for which the Drawbacks of Nicol prism, reflected light is found to be plane polarised is 1. Its costly due calcite crystal., called polarising angle ip., 2. Emergent ray is always displaced little to one side., 3. Emerging light is not uniformly plane polarised, 7.2.26 What is interference of light?, Phenomenon of superposition of two light 4. Field of view is quite limited., waves produce increase in intensity at some points, and decrease in intensity at some other points is, called interference of light

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7.3.3What are Uses of Polaroids, 1. Polaroids are used to avoid glare., 2. used in holography., 3. used in liquid crystal display (LCD)., 4. used to improve colour contrast in old oil, paintings., 5. used as window glasses to control the intensity of, incoming light., 6. Polarised laser beam acts as needle to read/write, in compact discs (CDs)., 7.3.4 State and Prove Malus’ law, Transmitted light intensity I from the, analyser is directly proportional to the square of the, cosine of the angle θ between the transmission axis, of polariser and analyser., Let I0 be the intensity and a be the amplitude of the, electric vector of light transmitted by the polariser., acosθ and asinθ are the parallel and perpendicular, components of amplitude a. Only (acosθ) component, will be transmitted by the analyser., The intensity of light transmitted from the analyser, is proportional to the square of the component of the, amplitude transmitted by the analyser., , 7.3.6 Obtain the equation for Fresnel’s distance, In diffraction, bending is not seen till the, diffracted ray crosses the width of central maximum at, a distance z from the slit. Distance upto which the ray, optics is obeyed and beyond which the ray optics is, not obeyed; but, the wave optics becomes significant, is called Fresnel’s distance., , 7.5.1 Obtain the equation for bandwidth in Young’s, double slit experiment, d is the distance between the double slits S 1, and S2. λ is the wavelength of coherent sources. D is, the distance of screen and double slits., The mid-point of S1 and S2 is C and the midpoint of the screen O is equidistant from S1 and S2. P is, a point at a distance y from O. The waves from S1 and, S2 meet at P either in-phase or out-of-phase, depending upon the path difference δ between the, two waves. S1M is drawn ꓕ to S2P., , 7.3.5 Discuss about pile of plates., Pile of plates converts partially polarised, refracted light into plane polarised beam based on, brewster law. several plates are kept one behind the, other at an angle 𝟗𝟎𝟎 -i𝒑 with the horizontal surface., So, light falls on these plates at i𝒑., , Above Formulas given distance of nth bright and nth, When unpolarised light passes successively through the dark fringe from centre O. Bandwidth β is the, plates, few parallel vibrations to the surface, present distance between any two consecutive bright (or), in the refracted light, gets reflected at the succeeding dark fringes., plates. Both reflected and the refracted lights are found, to be plane polarised.

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7.5.2 Obtain the equation for resultant intensity due to, interference of light, Two light waves from the two sources S1 and S2 are, meeting at point P., , a1 and a2 are the amplitudes of first and second wave ω, is the same angular frequency, and ϕ phase difference, between them., , On either side of central maximum, different higher, order diffraction maxima are formed, 7.5.5 Discuss the diffraction at single slit and obtain the, condition for nth minimum, A plane wavefront falls normally on a single, slit AB of width a. The diffracted beam falls on a, screen kept at a distance D from the slit. The centre, of the slit is C. P is a point on the screen. All the light, reaching point P from different points on the slit make, an angle θ with the normal CO., For P to be minimum intensity, slit AB is divided into, even parts, so that effect of one is cancelled by other, , 7.5.6Discuss the diffraction at a grating and obtain the, condition for the m th maximum., A grating is a plane sheet of transparent material, on which opaque rulings are made. space between the, rulings act as slit of width 𝒂 and the rulings act as, obstacles having a definite width 𝒃., Combined width of a ruling and a slit is called, grating element 𝑒 = 𝑎 + 𝑏. The points on the slit, separated by a distance equal to the grating element are, called corresponding points., Monochromatic light of wavelength λ is, incident on the grating. As the width of the slit is, comparable to that of wavelength, the incident light, undergoes diffraction. A diffraction pattern is, obtained on the screen using a convex lens., Path difference δ between the diffracted waves, from any pair of adjacent corresponding points on, reaching P is ,

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eye. The eyepiece acts as simple microscope and, produce an enlarged and virtual image. The inverted, image formed by the objective is adjusted within the, focus of the eyepiece so that the final image is formed, nearly at infinity (or) at the near point. The final image, is inverted with respect to the object., For P to be maximum intensity, slit AB is divided into, odd parts, so that one part is left uncancelled, , 7.5.3 Describing simple microscope, obtain equations, for magnification for near point and normal focusing., A simple microscope is a magnifying convex, lens of small focal length. It produces an erect,, Tube length L of microscope is, magnified and virtual image of the object. Object, the distance between the focal point of, must be placed within the focal length f (between the, the, eyepiece, and, the focal point of the objective., points F and P) on one side of the lens and image is, viewed through the other side., , This is magnification for near point focusing, , angular magnification is defined as the ratio of angle θi, subtended by the image with aided eye to the angle, θ0 subtended by the object with unaided eye., This is the magnification, for normal focusing., 7.5.4 Explain about compound microscope and obtain, the equation for the magnification., Compound microscope has two lenses. The, objective lens O near the object, forms a real,, inverted and magnified image of the object. This, image acts as object for the eyepiece lens E close to the, , Prove law of reflection using Huygens’ principle, Wavefront AB is incident on a reflecting plane, surface XY. When the wavelet from point B touches the, reflecting surface at 𝑩′ , the wavelet from point A would, have reached 𝑨′ .reflected wavefront 𝑨′ 𝑩′ emanates as a, plane wavefront., As reflection happens in the same medium, the, speed of light is same before and after the reflection., The time taken for the light to travel from B to 𝑩′ and A, to 𝑨′ are the same. distance B𝑩′ = distance A𝑨′ .

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8.2.1 Define work function of a metal. Give its unit., Minimum energy needed for an electron to, escape from the metal surface is called work function, of that metal. Unit: electron volt (eV), 8.2.2. What is photoelectric effect?, Ejection of electrons from a metal plate when, electromagnetic radiation of suitable frequency fall, on metal is called photoelectric effect, 8.2.3. Give the definition of intensity of light with unit., Intensity of light is equal to number of same, energy photons incident per unit area per unit time., unit : Wm–2., 8.2.4. How will you define threshold frequency?, Minimum, frequency, above, which, photoelectrons are emitted is called the threshold, frequency., 8.2.5What is a photo cell? Mention the different types, of photocells., 1), Photo electric cell converts light energy into, electrical energy. Its Types are, 1) Photo emissive cell, 2), 2) Photo voltaic cell, 3) Photo conductive cell., 8.2.6. State de Broglie hypothesis., Waves are associated with all moving, elementary particles like electrons, protons,, neutrons., 8.2.7. Why we do not see the wave properties of a, baseball?, Wave nature of matter is applicable for, microscopic atomic level but really negligible for the, macroscopic baseball., 8.2.8. A proton and electron have same kinetic energy., Which one has greater de Broglie wavelength., , 8.2.12 What are the applications of X-rays, 1. X-rays are used to detect fractures, 2. X-rays are used to cure skin diseases, tumors, 3. X-rays are used to check for flaws in welded joints., 4. X-ray diffraction is used to study the structure of, atoms and molecules in crystals., 8.2.13Why do metals have a large number of free, electrons?, In metals, Even at room temperature, the, electrons in the outer most shells are loosely bound, to the nucleus. So,large number of free electron move, inside the metal in a random manner., 8.2.14. What is surface barrier?, The potential barrier which prevents free, electrons from leaving the metallic surface is called, surface barrier., 8.2.15 Mention the two features of x-ray spectra, not, explained by classical electromagnetic theory., 1. For a given accelerating voltage, the minimum, wavelength or cut-off wavelength of continuous x-ray, spectra is same for all targets., 2. The intensity of x-rays is significantly increased at, certain well-defined wavelengths., 8.2.16 what is Bremsstrahlung?, Interaction between fast moving electron and the, nucleus changes the path of electron by changing speed, of electron. Radiation produced by decelerating, electron is called Bremsstrahlung or braking, radiation, 8.2.17 Differentiate Continuous and Characteristic Xray, Spectra, , De Broglie wavelength is inversely, proportional to square root of mass. Mass of electron, is lesser than mass of proton. So Electron has, Greater De Broglie wavelength., 8.2.9An electron and an alpha particle have same kinetic, energy. How are the de Broglie wavelengths related?, , De Broglie wavelength is inversely, proportional to square root of mass. Mass of electron, is lesser than mass of alpha particle. So Electron has, Greater De Broglie wavelength than Alpha particle., 8.2.10 What are types of Electron emission, 1.Thermionic Emission, 2.Field Electric Emission, 3.Photo Electric Emission, 4.Secondary Emission, 8.2.11 Define Stopping potential, Minimum Negative Potential given to Anode, to stop Most Energetic Electron is called Stopping, potential., , 8.3.1 List out the laws of photoelectric effect., 1.Minimum frequency above which photoelectrons, are emitted is called the threshold frequency., 2.Instantaneous Process .There is no time gap between, incidence of light and ejection of photoelectrons., 3.Number of photoelectrons and Saturation current, emitted is directly proportional to the intensity of, the incident light., 4.Maximum kinetic energy of the photo electrons is, directly proportional to the frequency of incident, light but does not depend on Intensity of Incident, Light., , 8.Dual Nature of Radiation and Matter S.Jayachandran, PG.Asst, GHSS, Manali,ThiruvallurDt, 9840430109 Page 34

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8.3.2What are the uses of Photoelectric Cells, 1. Photo cells are used as switches and sensors., 2. Street lights are Automatically turned on when it, gets dark using photocells., 3. Sounds are reproduced in motion pictures using, Photocells., 4. Athlete’s speed is measured using photocells., 5. Light intensity can be measured using Photocells., 8.3.3 Derive an expression for de Broglie wavelength, , 8.3.4 Derive an expression for de Broglie wavelength, for electron, An electron of mass m is accelerated through a, potential difference of V volt. The kinetic energy K of, the electron is equal to electrostatic potential energy, Ve., , 8.3.5 Write the Characteristics of photons, 1. Energy of photons of frequency ν: E=hυ, 2. Photons travel with the velocity of light and its, momentum is p=hν/c, 3. Photons are electrically neutral, Photons are, unaffected by electric and magnetic fields., 4. When a photon interacts with matter, the total, energy, total linear momentum and angular, momentum of photon are conserved. Number of, photons may not be conserved, 5. Energy of a photon is determined by the, frequency of the radiation and not by its intensity., 8.3.6 Give the construction and working of photo, emissive cell., Photo electric cell converts light energy into, electrical energy. Two metallic electrodes, a cathode, and an anode are fixed in an evacuated glass or, quartz bulb. Semi-cylindrical cathode C is coated with, a photo sensitive material. The anode A is a thin rod or, wire. A potential difference is applied between the, anode and the cathode through a galvanometer., , 8.3.7 Explain why photoelectric effect cannot be, explained on the basis of wave nature of light., According to wave theory, light of greater, intensity should impart greater kinetic energy to the, ejected electrons. But, maximum kinetic energy of, the photoelectrons emitted does not depend on the, intensity of the incident light., According to wave theory, even if light of low, frequency is incident on the surface, electrons should, be ejected. But, photoelectric emission is not possible, below a certain minimum frequency., According to wave theory, electron needs large, time to get liberated from the surface to overcome, the workfunction. But, photoelectric emission is an, instantaneous process., Therefore, the wave theory fails to explain the, existence of threshold frequency, How do we obtain characteristic x-ray spectra?, X – ray line spectrum showing narrow peaks, at some well – defined wavelengths is called, characteristic x – ray spectrum. This spectrum is due, to the electronic transitions within the atoms, when the, target is hit by fast electrons., When an energetic electron knocks some of, the K-shell electrons, vacancy is created. Electrons, from outer orbits jump to fill up the vacancy in the, K-shell. Energy difference between the levels is given, out in the form of x– ray photon of definite, wavelength. Such definite wavelengths, are the, characteristic of the target ., , K-series in the x-ray spectrum of an element arises, due to the electronic transitions from L, M, N, . ., levels to the K-level., Longer wavelength L-series in the x-ray spectrum of, an element arises due to the electronic transitions, from M, N, . . levels to the L-level and so on., , 8.Dual Nature of Radiation and Matter S.Jayachandran, PG.Asst, GHSS, Manali,ThiruvallurDt, 9840430109 Page 35

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8.5.1.Derive Einstein’s photoelectric equation, 4. Intensity of electrons scattered by Ni atoms in, When a photon of energy hν is incident on a, different directions are measured by the electron, metal surface, it is completely absorbed by a single, detector., electron and the electron is ejected., 5. Angle θ between the incident beam and the scattered, From the law of conservation of energy, beam can be changed by rotating detector., 6. A graph is plotted for intensity of the scattered, electron beam and angle θ., , This is Einstein Photoelectric Equation., If the electron does not lose energy by internal, collisions, then electron is emitted with maximum, 7. For accelerating voltage V=54V, the scattered, kinetic energy 𝑲𝒎𝒂𝒙 ., wave shows a peak at an angle of 50° . Rise in, intensity is due to the constructive interference of, electrons diffracted from various atomic layers, of the target material., A graph between 𝑲𝒎𝒂𝒙 of the photoelectron and, frequency ν of the incident light is a straight line.The 8. Knowing the value of interplanar spacing of Nickel,, the wavelength of the electron wave was, slope of the line is h and its y-intercept is −𝝓𝟎, experimentally calculated as 1.65 A0., 8.5.2 Explain the working of Electron Microscope, 9. wavelength calculated by de Broglie relation, forV=54 V agrees, with calculated value., 8.5.4 Explain the effect of potential difference on, photoelectric current, Frequency and intensity of the incident light, falling on cathode C are kept constant. When potential, of anode A is increased, photocurrent increases and, reaches a saturation current at which all the, photoelectrons from C are collected by A., When a negative potential is applied to A with, respect to C, the current does not immediately drop, to zero. Photoelectrons overcomes the retarding electric, field and reach the electrode A. When the negative, the image of the sample., 6.Magnified image is obtained on the screen by potential of A is increased, Photocurrent becomes, zero at a particular negative potential V0, called, magnetic objective projector lens system., Electron microscope is used in all branches of science. stopping or cut-off potential. kinetic energy of the, 8.5.3.Describe briefly Davisson – Germer experiment fastest electron is equal to the work done by the stopping, potential. Minimum Negative Potential given to, which demonstrated the wave nature of electrons., Davisson and Germer demonstrated that Anode to stop Most Energetic Electron is called, electron beams incident on crystals are diffracted off Stopping potential, in certain specific directions., 1. Electrons are emitted from the hot filament by, thermionic emission., 2. Electrons are accelerated due to the potential, difference of high tension (H.T.) battery between, the filament and the anode aluminium cylinder., 3. After passing through, two thin aluminium, diaphragms electron beam strike Nickel crystal., 8.Dual Nature of Radiation and Matter S.Jayachandran, PG.Asst, GHSS, Manali,ThiruvallurDt, 9840430109 Page 36