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Curbag, , iNeed, he, , Lace a4, , , , , , , , Electricity, , ‘ ent form of ’, convenict f cnerpy. Itis being used in almost every f, sector of modern society like, , sholds, commercia, hou' rial, transport and industry, etc., to make life faster, c ke faster and easier., , Electric Charge and Current, Electric Charge, , Acharge is a physical entity which is defined by excess or deficiency of electrons on a body., , Abody is said to be negatively charged, if it gains electrons. e.g. An ebonite tod rubbed, with fur acquires negative charge. A body is said to be positively charged, if it loses, , dectrons. e.g. A glass rod rubbed with a silk cloth acquires positive charge., , The SI unit of electric charge is coulomb (C)., The total charge acquired by a body is an integral multiple of magnitude of charge on a, , single electron. This principle is called quantisation of charge., , -19, * Magnitude of charge on one electron, ¢ =~ i 1 C., =ne =n 1.6% 10°C., , San, Charge on 7 electrons, 7 —_ PC, c= 5 , * Magnitude of charge on one, , Electric Current, , It is defined as the rate of flow 0, in unit time., , Ifqamount of char, , proton,, , f electric charge through any cross-section of a conductor, cl, in ctime, then, flows through 4 conductor inf time, the!, , = " 1 cl ie | oe, , - ——— Charge) ™ | _—, Electric current ()* on ee, ” yugh the condu, , ctor., , — —_ Ang thre, where, 1 = number of electrons flowing, n=, , , , One of the most essential part of life in toda Sw { eT, y orld is electricity, y It isa controllable and, , © Bectrc C, © Bectne P, Ditterencs, © Electric C, © Om's, © Rewstan, Resstan, Resustort, Hosting, Corer, © Brectnc |
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334, , — cc, , Allynone Science Class ig, ), , , , , , The SI unit of electric current is ampere (A), named in, honour — of French — scientist Andre-Marie Ampere, (1775-1836), It is a scalar quantity,, , When 1 coulomb of tge flows through any cross-section, ofa conductor in | second, then the electric current flowing, through it is said to be 1 ampere,, 1 coulomb, —m, , , , , , , , , , 1As—=, , ie, 1 ampere =, 1 second Is, , Smaller units of current are milliampere, (li mA = 10 A) and microampere (I tA = 107°A),, , Direction of Electric Current, , The direction of electric Current is taken as opposite to the, direction of the flow of electrons (negative charges). In an, electric circuit the current flows from positive terminal of the, cell to the negative terminal,, , Flow of Charges Inside a Wire, , Inside a solid, the atoms are packed together very closely to, each other but electrons are able to travel through the solid, crystal as if they were in vacuum. When a steady current flows, in a conductor, then the electrons in ic move with a certain’, average drift speed (the constant speed of the electrons inside, the conductor with which they move under the effect of, , " external electric supply) of the order of 1074 m/s, Thus, flow, of charges (i.e. electrons) produces current in a wire., , Ammeter, , Electric current is measured by a device called ammeter. It is, a low resistance device which is always connected in series, with the device through which the current is to be measured,, , Example 1. A current of 150 mA flows through a, circuit for 2 min. Find the amount of charge that flows, through the circuit., Sol. Given, Current, J =150 mA =150x1079 A, , Time, t=2 min =2x60=120s, , Amount of charge, g =?, , We know that, g=/ xt :, , => q =150x107 x 120, , > q=18C, , So, 18 C of charge flows around the circuit., Example 2. A total of 6x 10“ electrons flow through, a current carrying conductor when connected through, an external power supply for 20 s. Find the value of, current in the conductor., , , , Sol. Given, ‘Tu, Time, ¢ = 205, We know that, q =ne (i), , [from the principle of quantisation of electric charge}, , roti “ s. 46, [number of electrons, = 6x10 clectrons, Current, J =?, , , , , , [ad, t, From Eqs. (i) and (ii), we get, Pa ME 6X10 x 16x10°, t 20, =0.48x1077A = 48x 102A,, , Thus, the current through the conductor is 4.8 x 104,, , Electric Potential and, Potential Difference, , Electric Potential, , It is defined as the amount of work done when a \, positive charge is moved from infinity to a point., Ifwork done in moving a positive charge q from infinity, point is W, then electric potential V of that point is, , vel, , q, , The ST unit of electric potential is volt (V) and is named a, Italian physicist Alessandro Volta (1745-1827). It is a sc, quantity., , Electric Potential Difference (AV), , It is defined as the work done per unit charge in movit, unit positive charge from one point to other point,, , and, , sei), , , , [ve =16x 107g], , , , , , , , , , The electric potential difference between two points is, to be 1 vole, if 1 joule of work is done in moving 1 coulo, of electric charge from one point to other point., , Thus, 1 volt= dyoule, coulomb, "J, , > 1V=—, 1C, , > 1V=1J/C=1JC"!, , Smaller units of electric potential,, ImV=10°V, 1pv=10-Sv, , Larger units of electric potential,, 1kV=10? V, IMV=10°y, , a Mid
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“JEG EIACITICITY, , _ 335, , , , , , , J, , sctric potential difference between two points ina El ect r C Ci rcu it, , it is measured using a device called i i i, , ee eae wk a okie i is high Aclosed and continuous path through which electric current, 1, , Be Gombonentt) through which potential difference is to be flows is known as electric circuit. It has various components, ed., , , , including a source of current (say a cell or battery), a load, xample 3. Ho | ; (say a bulb or any other appliance), a switch/key (to open or, Large of 3 C acres ee work is done in moving a close a circuit), a fuse, all connected through connecting, Giierence 152 points having a potential wires. These wires are generally made of copper., sol. Given, charge, q=3C; Potential di When the key is closed, then the circuit is called closed, " Reeuramns Ebi 2 fetes AV =15V circuit. This means that current would flow through the, of work done in moving the charge circuit to operate the device. When the key is open, then the, W =Vq=15x3=45), , circuit is called open circuit. This means that current would, , example 4. Calculate the potential difference not flow through the circuit., , petween two terminals of a battery, if 100 J of work is, , required me ate the charge of 20 C from one Circuit Diagram, , inal of the battery to t!, , ates ty to the other. It is a schematic diagram which represents the relative, gol. Given, Work done, W = 100 J; Charge, g = 20 C, , positions and connections of various. circuit components, , Potential difference, AV =? represented by their symbols., , We know that, AV a — 100 _, q 20, ‘The potential difference between two points is 5 V., example 5. How much work is done in moving a, charge of 2 C from a point of 118 V to a point at 128 V?, Sol. Given, Charge, g=2C, Potential at point A, V4 =118 V, Potential at point B, Vz =128 V, Work done, W =?, , , , , , , , , , , , , A schematic diagram of an electric circuit having cell,, , , , , , , , , , , , , , , , We know that, electric bulb, ammeter and plug key, sPovstial dienes AY 4 a =10V Symbols used in Electric Circuits, tWork done, W =AVx g=10x2=20J Circuit Components Descriptions Symbols, So, the work done in moving the charge is 20 J. ‘An electric cell Provides, constant potential, difference between Aye, two points, Battery Combination of two 4 4 4 i, c ‘or more cells, 1 itabody has positive charge, then what does it mean? connected, 2 Inwhich direction does current flow in an electric circuit? in series, 3 The charge on an electron is 16 x 40°C. Find the number of Electric bulb Circuit components @ ®, il or, electrons that will flow per second to constitute a current of 2A., tans. 126 «10 secre) Resistor or resistance Controls current fs ww, 4 Write a low resistance device name which is always canierlee howe through the, in series with the device through which the current sto P@, measured Rheostat or variable Provides variable ny, . intini i j resistance Of or, 5 tiwork done in moving a charge of 20 mC from infinity to @ an resistance potential Gvider Be, ~ Oin an electric field is 15 J, then what is the electro potential, , 2 AWW, ‘his point? ee, , 8 We _, Wite a high resistance device name which is always connected, "parallel,
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eee, , , , Circui, < uit Components Descriptions Symbols, mmeter, , r Measures current pee, , flowing through —@)—, , Circuit, , , , , , Voltmeter Messures Potential +, Moan between —V)—, ae or Plug key Open the-circuit —=>—, fe, pid Plug key Close the circuit —)— or 4, Fuse Safety device —0~O—, Wires joint — ae, , —, , Ohm's Law, , This law was given by a German Physicist Georg Sitnon, Ohm (1787-1854) in the year 1827. It gives a relationship,, between current J, flowing in a metallic wire and potential, difference V, across its terminals. i, According to this law, the electric current flowing through a, conductor is directly proportional to the potential difference, applied across its ends, providing the physical conditions, (such as temperature) remain unchanged. :, If V is the potential difference applied across the ends of a, conductor through which current J flows, then according to, , Ohm’s law,, , , , Wires crossing, without joining, , , , Vol [at constant temperature], , poh, R, , , , , , IR, , or, , 4, , , , , , or, , , , , , , , , , where,, of the conductor at a given temperature., , From the above formula, f 1, proportional to resistance. If resistance is doubled, then, , if resi i current, current gets halved and if resistance is halved, then, , gets doubled., , Note The conductors which obey O! ;, conductors while the conductors which do not, , law are called non-ohmic conductors., , nm’s law are called ohmic, t obey Ohm's, , it is clear that current is inversely _, , Waste TeUAES SCIENCE Clas wa, h, , V-/Graph, , The graph between the potential difference V ang th, le, , corresponding current J is found to be a, , straight line, , passing through the origin for ohmic (metal) condy, Ctors,, , Y, , Potential, difference, V —, , , , ‘ ° Current, 7 —>, V-[ graph for metal conductor, ,, , Resistance, Itis that property of a conductor by virtue of which it, , opposes/resists the flow of charges through it. Its SI unitis, ohm and is represented by the Greek letter Q., , Resistance of a conductor is given by R =“., , It is said to be 1 hin if a potential difference of 1 volt actos, , Ris the constant of proportionality called resistance, , the ends of the conductor makes a current of 1 ampere t, flow through it., , ie. ‘olin 1 PO, ‘ 1 ampere, => 192) -1 va" *, 1A, , Example 6. The potential difference between the, terminals of an electric heater is 75 V when it draws, a current of 5A from the source. What current will th, heater draw, if the potential difference is increased t, 150 V? ?, Sol. Given, Potential difference, V=75 Vy, , Current, T=5A, , pa2=150, 5, , We know that, R= “, , “ When potential difference is increased to150 V, then curter, , JL aM 2150 Liga, R15, , So, the current through the heater becomes 10 A.
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5, , , , dlectrical devices, where hj nije |, . . STAN S Ce, reduces current in a circy aru!, , Wired, Tt, , it, ep ‘, & nichrome,, , + alloys like r, iable resi ;, , Rheostat/variab 7 fesistance Itisa variable fiona, is used to control the flow of electric current by ine, increasing or decreasing th py, , NC resistance,, , Good conductor A material which off, the flow of electrons or electric current in an clectri, circuit is known as a good conductor, cg. silver, ae, aluminium. Amongst these, silver is the best conduc, “sectticity. s ctor of, , manganin and constantan,, , manually, , ers low resistance to, , + Poor conductor A material wh, , ich offers hi, than conductors to the flow of ¢, , gher resistance, , tors tothe! electrons or electric current, in an electric circuit is known as Poor conductor, eg., mercury, lead, stainless steel, alloys of iron and, chromium., , « Insulator A material which offers very, the flow of electrons or electric current in an clectric, , circuit is known as insulator, e.g. rubber, dry wood and, plastic. Electric current does not flow through them,, , Factors on which the Resistance, ie Conductor Depends, , The electrical resistance of a conductor depends on the, following factors:, , high resistance to, , () Length of the conductor The resistance of a, conductor R is directly proportional to its length /., , , , Since, the resistance of a wire is directly proportional, , to its length, ic. when the length of a wire is, , doubled/halved, then its resistance also gets, , doubled/halved. ‘eet, (ii) Area of cross-section of the we ae, , resistance of a conductor R is inversely prop, , to its area of cross-section A., , 1, ie. oe, , A, , , , , , u MS resistance, , * :, , thewinne Tea of cross-section of wire is, § Tesistance will get doubled., , ot 'S stretched (increased its lengthy, , we ee decreases accordingly but the, MBIH) Of the conductor remains the, , Note When ac ‘ondus, then its area of, Volume (i @, , same, , (ii) Nature of the n, , naterial of the cond Tl, . uctor, Fesistance of a con mice ig, , aa ductor depends on the nature of the, “ tal of which it is made, Some materials have low, “sistance, whereas others have high resistance,, , Therefore, from Eqs. (i) and (ii), we can write, , , , 1, Ra~ of, A, where, p is the constant of Proportionality and is, called resistivity or specific resistance of the, conductor., , Resistivity, , It is defined as the resistance of a conductor of unit length, and unit area of cross-section., , Its SI unit is ohm-metre, (Q-m)., The resistivity of a material does not depend on its length or, thickness but depends on the nature of the substance and, , temperature. It is a characteristic property of the material of, the conductor and varies only,, , , , its temperature changes., Insulators such as glass, rubber, ebonite, etc, have a very, , high resistivity (10'* t010"” Q -m), while conductors have a, very low resistivity (107* to 107° Q-m)., , Alloys have higher resistivity than that of their constituent, metals. They do not oxidise easily at high temperatures, this, is why they are used to make heating elements of divices, such as electric iron, heaters, etc. Tungsten is almost used, exclusively for filaments of electric bulbs, whereas copper, and aluminium are generally used for electrical transmission, lines. ,, Example 7. A wire of given material having length, and area of cross-section A has a resistance of 102, What would be the resistance of another i of the, same material having length 1/4 and area o!, , ection 2.5A?, cross-section 2. ail, , section =, , Sol. For first wire, length = 1, area of cross, , and resistance, R, =10 Q,
