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ELECTROMAGNETIC INDUCTION , AC & EM WAVES, , Electromagnetic induction, , 1. A coil of area Ao is lying in such a magnetic field, whose value changes from Bo to 4Bo in t second. The, induced emf in the coil will be, 3A o Bo, 4 A o Bo, 4Bo, 3Bo, (a), (b), (c), (d), t, Ao t, Ao t, t, 2. The magnetic flux passing normally through a coil is, given by  = 20sin5t + 5t² + 50 milliweber, where t, is in second. The value of induced emf in the coil at t, = 2 second will be, (a) 314 volt, (b) 334x103 volt, 3, (c) 284x10 volt, (d) zero, 3. A cylindrical bar magnetic is lying along the axis of a, circular coil. If the magnet is rotated about the axis of, the coil then, (a) emf will be induced in the coil, (b) only induced current will be generated in the coil, (c) no current will be induced in the coil, (d) both emf and current will be induced in the coil

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4. A conducting square loop of side, l and resistance R moves in its, place with a uniform velocity v, v, perpendicular to one of its sides., A, uniform and, constant, magnetic field B exists along the, perpendicular to the plane of the loop as shown in the, figure. The current induced in the loop is, Blv, Blv, (a), clockwise, (b), anticlockwise, R, R, 2Blv, (c), anticlockwise, (d) zero, R, 5. A magnet is taken towards a coil, (i) rapidly, (ii) slowly, The emf will be induced in the coil, (a) more in the second condition, (b) more in the first condition, (c) same in both conditions, (d) more or less depending upon the radius of the, coil, 6. A bar magnet is dropped vertically along the axis of a, horizontal copper ring. The acceleration of the, magnet will be, (a) a = g, (b) a > g, (c) a < g, (d) a = 0, 7. If a coil is rotated in a uniform magnetic field B from, 0 to 180° in time t, then Average induced emf, generated in the coil will be, (a) NAB (b) NAB/t, (c) 2NAB/t, (d) zero, 8. A magnet is, brought, v, S, N, towards, a, coil C as, G, shown in the, figure. The direction of induced current in the circuit, will be as seen from magnet side, (a) anticlockwise (b) clockwise (c) north (d) south, 9. A bar magnet is released from rest along the axis of a, very long, vertical copper tube. After some time the, magnet, (a) will stop in the tube, (b) will move with almost constant speed, (c) will move with an acceleration g (d) will oscillate, 10., Figure (a) shows a conducting loop being pulled, out of a magnetic field with a speed v. Which of the, floor, P, plots, d c, shown, a, v, in the, b, figure, (b), V, (a), may, (b), represe, nt the power delivered by the pulling agent as a, function of the speed v?, 11.In the figure shown, the north, pole of a magnet is brought, towards a closed loop consisting, N, S, a condenser. Positive charge will, C, be produced on, A B, (a) Plate A, (b) Plate B, , (c) both on plate A and plate B, (d) neither on plate A nor on plate B, 12. When a conductor is rotated in a perpendicular, magnetic field then its free electrons, (a) move in the field direction, (b) move at right angles to field direction, (c) remain stationary, (d) move opposite to field direction, 13.If the magnetic field in the, following figure is increased, A, then, B, (a) plate A of the condenser, will get positively charged, (b) plate B of the condenser will get positively, charged, (c) the condenser will not be charged, (d) both the plates will be charged alternately, 14. A conducting rod AB of length l = 1 m is moving at a, velocity v = 4 m/s, v, making an angle 30°, with its length. A, 30°, B, uniform, magnetic A, field B = 2 T exists in, a direction perpendicular to the plane of motion., Then, (a) VA  VB = 8 V, (b) VA  VB = 4 V, (c) VB  VA = 8 V, (d) VB  VA = 4 V, 15. A metallic rod of length l rotated, v, P, with angular velocity  in a, uniform magnetic field as shown, l, in the figure. The induced emf, O, between the ends of the rod will be, B, , (a) Bl² (b) Bl (c) zero(d) Bl²/2, 16. A metal conductor of length 1m rotates vertically, about one of its ends at angular velocity 5 radians per, second. If the horizontal component of earth’s, magnetic field is 0.2 ×10-4T, then the e.m.f., developed between the two ends of the conductor is, (a) 5mV (b) 50μV (c) 5μV (d) 50mV, , 17. A conducting square loop of side L and, resistance R, x x x x x, moves in its plane, with a uniform, x x x x x, V, velocity v, L, perpendicular to, x x x x x, one of its side. A, magnetic, x x x x x, induction B, constant in time and space, pointing, perpendicular and into the plane at the loop, exists everywhere with half the loop outside the, field, as shown in figure. The induced emf is, (a) zero (b) RvB (c) VBL/R, (d) VBL, 18. A coil having n turns and resistance RΩ is, connected with a galvanometer of resistance, 4RΩ.This combination is moved in time t seconds, from a magnetic field W1 weber to W2 weber. The

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induced current in the circuit is, (W2  W1 ), n(W2  W1 ), (a), (b), Rnt, 5Rt, (W2  W1 ), n(W2  W1 ), (c), (d), 5Rnt, Rt, Induced electic field, 19. The following field line can never represent, (a) induced electric field, (b) magnetostatic field, (c) gravitational field of a mass at, rest, (d) electrostatic field, 20.A small bar magnet is being slowly inserted with, constant, velocity, inside a, solenoid as, shown in figure. Which graph best represents the, relationship between emf induced with time, emf, , emf, , (a), , Induced Electic field, , (b), Time, , 23. A thin semi-circular conducting ring of radius R is, falling with its plane vertical in, x x x x x, horizontal magnetic, , B, x x x x x, induction B . At the position, N, MNQ the speed of the ring is v,, x xv x x x, and the potential difference, M, Q, developed across the ring is, (a) zero, (b) BvπR2/2 and M is at higher potential, (c) πRBv and Q is at higher potential, (d) 2RBv and Q is at higher potential., , Time, emf, , emf, , (c), , (d), Time, , Time, , 21. An infinitely long cylinder is kept parallel to an, uniform magnetic field B directed along positive z axis. The direction of induced current as seen from, the z axis will be :, (a) zero, (b) anticlockwise of the +ve z axis, (c) clockwise of the +ve z axis, (d) along the magnetic field, , 22 The flux linked with a coil at any instant ‘t’ is, given by φ= 10t2-50t+250, The induced emf at t = 3s is, (a) -190V (b) -10V (c) 10V, (d)190V, , 24.A metallic sheet is, N, lying in magnetic, field which is, increasing from, zero to maximum. W, The induced, current are, produced as, S, shown in the, figure. The direction of magnetic field will be, (a) normal to plane of paper downwards, (b) normal to plane of paper upwards, (c) from east towards west, (d) from the north towards south, , Mutual & Self induction, , E

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1. Electric current is flowing in same direction in two, coaxial coils. On increasing distance between two, coils the value of current will, (a) decrease, (b) increase, (c) remains unchanged, (d) nothing can be said, 2. Two coils P and Q are, lying in a little, I, distance, apart, coaxially as shown in observer P, Q, the figure. If a current, I is suddenly setup in, the coil P then the direction of current induced in coil, Q will be, (a) clockwise, (b) towards north, (c) towards south, (d) anticlockwise, 3. Two similar circular coaxial loops carry equal, currents in same direction. On bringing the loops, closer together the current in, (a) each loop will decrease, (b) each loop will increase, (c) both loop will remain same, (d) one loop will increase and in second loop will, decrease, 4. Two circular loops of equal radii are placed coaxially, at some separation. The first is cut and a battery is, inserted in between to drive a current in it. The, current changes slightly because of the variation in, resistance with temperature. During this period, the, two loops, (a) attract each other, (b) repel each other, (c) do not exert any force on each other, (d) attract or repel each other depending on the sense, of the current, 5. The coefficient of mutual induction between two, coils is 1.25 H. If the rate of fall of current in the, primary is 80 Amp/s, then the induced emf is the, secondary coil will be, (a) 100 V, (b) 64 V (c) 12.5 V, (d) 0.016 V, 6. Two circular conducting loops of radii R1 and R2 are, lying concentrically in the same plane. If R1 >> R2, then the mutual inductance (M) between them will be, proportional to, R2, R2, R, R, (a) 1, (b) 2, (c) 1, (d) 2, R2, R1, R2, R1, 7.Two coaxial coils are very close to each other and their, mutual inductance is 5 mH. If a current 50 sin 500t is, passed in one of the coils then the peak value of, , induced emf in the secondary coil will be, (a) 5000 V (b) 500 V, (c) 150 V (d) 125 V, 8. The coefficient of mutual induction between two, closely lying coils does not depend upon, (a) their mutual orientation, (b) the permeability of their core material, (c) their structure, (d) the current flowing in them, 9. Two coils are placed close to each other. The mutual, inductance of the pair of coils depends upon, (a) the rates at which current are changing in, the two coils, (b) relative position and orientation of the two, coils, (c) the materials of the wires of the coils, (d) the currents in the two coils, 10. Two coils A and B have coefficient of mutual, inductance M = 2H. The magnetic flux passing, through coil A changes by 4 Weber in 10 seconds, due to the change in current in B. Then, (a) change in current in B in this interval is 0.5 A, (b) the change in current in B in this interval is 2 A, (c) the change in current in B in this interval is 8 A, (d) a change in current of 1A in coil A will produce, a change in flux passing through B by 4 Weber, 11. The value of mutual inductance can be increased by, (a) decreasing N, (b) increasing N, (c) winding the coil on wooden frame, (d) winding the coil on china clay, 12. The value of coefficient of mutual, induction for the arrangement of, S, two coils shown in the figure will, be, P, (a) zero, (b) maximum, (c) negative, (d) positive, 13.The current-time (I-t) curve for, I, an inductance coil is as shown, in the figure. The voltage, variation will be, t, E, , E, , (a), , (b), t, , t, , E, , (c), , E, t, , (d), , t, , 14. The current in the primary of a car spark coil changes, from 4 A to 0A in 10 microseconds as a result of, which and emf of 40 kV in induced in the secondary., The coefficient of mutual induction between the, primary and the secondary of spark coil will be, (a) 10 H, (b) 1 H, (c) 0.1 H, (d) zero

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15. A small coil of radius r is placed at the centre of a, large coil of radius R, where R >>r. The two coils are, coplanar. The mutual induction between the coils is, proportional to, r2, r, r, r2, (b), (c), (d), R, R, R2, R2, 16. The self-inductance of a coil is 5 mH. If a current of, 2A is flowing in it then the magnetic flux produced, in the coil will be, (a) 0.01 Wb (b) 10 Wb, (c) zero, (d) 1 Wb, 17.The coefficient of self-induction of two coils are L1, and L2. To induce an emf of 25 V in the coils change, of current of 1A has to be produced in 5 second and, 50 ms respectively. The ratio of their selfinductances L1:L2 will be, (1) 1:5, (b) 200:1, (c) 100:1, (d) 50:1, 18. When a coil is wound on a core of relative, permeability µ then its self-inductance becomes, (a) L, (b) L/µ, (c) µL, (d) µL², 19. The coefficient of self-induction of two inductance, coils are 0.01 H and 0.03 H respectively. When they, are connected in series so as to support each other,, then the resultant self-inductance becomes 0.06, Henry. The value of coefficient of mutual inductance, will be, (a) 0.02 H, (b) 0.05 H, (c) 0.01 H (d) zero, 20. Two coils are at fixed locations. When coil 1 has no, current and the current in coil 2 increases at the rate, 15 A/s there emf in coil 1 in 25 mV, when coil 2 has, , (a), , no current and coil 1 has a current of 3.6 A, the flux, linkage in coil 2 is, (a) 16 mWb (b) 10 mWb (c) 4 mWb (d) 6 mWb, 21. The self-inductance and resistance of a coil are 5 H, and 20  respectively. On applying an emf of 100 V, on it, the magnetic potential energy stored in the coil, will be, (a) 62.5 Joule, (b) 62.6 erg, 3, (c) 62.5x10 Joule, (d) zero, 22. The inductance between A and D is, A, , 3H, , 3H, , 3H, , D, , (a) 3.66H (b) 9H (c) 0.66H (d) 1H, 23. When the current changes from +2A to -2A in 0.05, second, an e.m.f. of 8 V is induced in a coil. The, coefficient of self-induction of the coil is, (a) 0.2 H (b) 0.4 H (c) 0.8 H (d) 0.1 H, 24. Two coaxial solenoids are made by winding thin, insulated wire over a pipe of cross-sectional area A =, 10 cm2 and length = 20 cm. If one of the solenoid has, 300 turns and the other 400 turns, their mutual, inductance is (μ0 = 4π ×10-7TmA-1), (a) 2.4π × 10-5-H, (b) 4.8π × 10-4H, -5, (c) 4.8π × 10 H, (d) 2.4π × 10-4H, , Alternating Current

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Average,Mean & RMS, , (d) undefined for a direct current, 12. The average, Y, and effective, values for the, Vm, wave shape O, , shown here in, the figure are, V, 2, Vm and m, , 2, Vm, 2, (c) Vm and, , 2, , (a), , 1. In an alternating emf E = Eo cost the peak value of, voltage is 10 V and its frequency is 50 Hz. The, instantaneous value of emf at t = 1/600 sec will be, (a) 10 V, (b) 53 V, (c) 5 V, (d) 1 V, 2. The peak value of an alternating emf is Eo. Its average, value over one time period will be, (a) Eo, (b) Eo/2, (c) Erms, (d) zero, 3. An alternating voltage source is connected in an A.C., circuit whose maximum value is 170 volt. The value, of potential at a phase angle of 45° will be, , 5., , 6., , 7., , 8., , Reactance, , 4., , (a) 120.56 V (b) 110.12 V (c) 240 V (d) zero, The frequency of a.c. is 50 Hz. How many times in, one second does the voltage in the circuit becomes, zero, (a) 25, (b) 50, (c) 100 (d) 150., What will be the equation of alternating current of, frequency 75 Hz if its R.M.S. value in 20 ampere, (a) I = 20 sin (150t), (b) I = 202 sin (150t), (c) I = 20/2 sin (150t), (d) I = 202 sin (75t), An AC source is rated 220 V, 50 Hz. The average, voltage is calculated in a time interval of 0.01 s. It, (a) must be zero, (b) may be zero, (c) is never zero, (d) is (220/2)V, The magnetic field energy in an inductor changes, from maximum value to minimum value in 5.0 ms, when connected to an AC source. The frequency of, the source is, (a) 20 Hz (b) 50 Hz (c) 200 Hz (d) 500 Hz, Which of the following plots, a, may represent the reactance of, c, a series LC combination?, b, Frequency, , d, , 9. A series AC circuit has a resistance of 4  and a, reactance of 3 . The impedance of the circuit is, (a) 5 , (b) 7 , (c) 12/7 (d) 7/12 , 10. An alternating current having peak value 14 A is, used to heat a metal wire. To produce the same, heating effect, a constant current i can be used where, i is, (a) 14 A, (b) about 20 A (c) 7 A (d) about 10 A, 11. A constant current of 2.8 A exists in a resistor. The, rms current is, (a) 2.8A, (b) about 2 A (c) 1.4 A, , 2, , 3, , rad, , Vm, V, and m, , 2, Vm, Vm, (d), and, 2, 2, , (b), , 13. In the equation of A.C. I = Io sin t, the current, amplitude and frequency will respectively be, I , , , (a) Io,, (b) o ,, (c) Imax,, (d) Io, , 2, 2, 2 2, 10, , +, , 1µF, , , , 14. A sinusoidal A.C. current flows in an inductor as, shown in the graph. I, T, P, The, potential, difference across, t, S, the inductor is, Q, R, maximum at the, instant indicated on the graph by the point, (a) P (b) Q, (c) R, (d) T, (e) S, 15. Alternating current can not be measured by D.C., ammeter because, (a) Average value of current for complete, cycle is zero, (b) A.C. Changes direction, (c) A.C. can not pass through D.C. Ammeter, (d) D.C. Ammeter will get damaged., 16., , A resistance of 20 ohm is connected to a source of an, alternating potential V = 220 sin (100t). The time taken, by the current to change from its peak value to rms value, is-, , (a) 0.2 sec, (c) 25 × 10–3sec, 17., , (b) 0.25 sec, (d) 2.5 × 10–3sec, , Alternating voltage (V) is represented by the equation, , (a) V(t )  Vmet, (b), V(t )  Vm sin t, (c) V(t )  Vm cot t, (d) V(t )  Vm tan t, where Vm is the peak voltage, 18., , An ac generator consists of a coil of 200 turns each of, 2, , area 80 cm and rotating at an angular speed of 200 rpm, 2, , in a uniform magnetic field of 4.8× 10 T. The rms values, of emf induced in the coil is, (a) 22.68 V, (b) 11.37 V, (c) 7.39 V, (d) 18.67 V

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21., , In an ac dynamo, the number of turns in the armature, are made four times and the angular velocity 9 times, then, the peak value of induced emf will become, , (a) 36 times, 18 times, 22., , (b) 12 times, , (d) 50 Hz, 200, , (b), f, , (b) 1/ 100 sec,, (d) None of these, , 19. The correct curve representing the variation of, capacitive reactance XC with frequency f is, XC, , XC, , (b), f, , f, XC, , (c), (d), 20. An RC circuit is as fshown in the figure. impedance, f, will be, (a) zero, (b) , (c) 1/c, (d) c, 21. A resistance of 10  and an inductance of 100 mH, are connected in series with an A.C. source of, voltage V = 100 cos (100t) volt. The phase difference, between the voltage applied and the current flowing, in the circuit will be, (a) zero, (b) /2, (c) /4, (d) , 22. In an LCR circuit the values of XL, XC and R are, 300 , 200  and 100  respectively. The total, impedance of the circuit will be, (a) 600  (b) 200 , (c) 141 , (d) 310 , , f, , R, , R, , (c), , (d), f, , (a) 1/200 sec, 1/ 100 sec, 1/200 sec, (c) 200 sec, 100 sec, , XC, , R, , (a), , (b) 400  Hz,, , If the frequency of an alternating current is 50 Hz then, the time taken for the change from zero to positive peak, value and positive peak value to negative peak value of, current are respectively, , (a), , R, , (d), , The equation of an alternating current is, i  50 2  sin 400 t ampere then the frequency and the, root mean square of the current are respectively, , (a) 200 Hz, 50 amp, 50 2 amp, (c) 200 Hz, 50 2 amp, amp, 10., , (c) 6 times, , 23. The correct curve between the resistance of a, conductor (R) and frequency (f) is, , f, , 24.An A.C. voltmeter in L-C-R circuit reads 30 volt, across resistance, 80 volt across inductance and 40, volt across capacitance. The value of applied voltage, will be, (a) 50 volt (b) 25 volt (c) 150 volt (d) 70 volt, 25. In the following circuit, the, 5, 0.01 H 10 F 25, values of L, C and R are 0.01H,, 105 F, 25  and 220 V, respectively. The value of, current following in the circuit, Eo=220V, at f = 0 and f =  will, ~, respectively be, (a) 8 A and 0 A, (b) 0 A and 0 A, (c) 8 A and 8 A, (d) 0 A and 0 A, 26. In an A.C. circuits, the current, (a) always leads the voltage, (b) always lags behind the voltage, (c) is always in phase with voltage, (d) may lead or lag behind or be in phase with voltage, 27. In an A.C. circuit XC = XL. The phase difference, between the current and voltage will be, (a) 0, (b) /4, (c) /2, (d) , 28. When the frequency of applied emf in an LCR, series circuit is less than the resonant frequency, then, the nature of the circuit will be, (a) Capacitive, (b) resistive, (c) Inductive, (d) all of the above, 29. The phase difference between the applied emf and, the line current in an anti resonant circuit at, resonance is, (a) /2 radian (b)  radian (c) 3/2 radian (d) zero, 30. The value of impedance at resonance in a series, resonant circuit is, 1, (a) R (b) 2 R (c) R 2  2L2 (d) R 2  2 2, C, 31.In the circuit shown, if the value, C, L, R, of resistance is 60 , then the, 15V, 20V 10V, current flowing through the, condenser will be, (a) 0.25 A, (b) 0.5 A, ~, (c) 0.75 A, (d) 1 A, 32.A series L-C-R circuit is resonant at 2000 Hz. If the, frequency of source is increased to 2500 Hz, then, which phase relation is correct?, (a) current will leas the voltage

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(b)voltage will lead the current by a phase angle of, /2, (c) voltage and current will be in same phase, (d) voltage will lead the current, 33., , When 100 volt dc is applied across a solenoid, a current, of 1.0 amp flows in it. When 100 volt ac is applied across, the same coil, the current drops to 0.5 amp. If the, frequency of ac source is 50 Hz the impedance and, inductance of the solenoid are, (a) 200 ohms and 0.5 henry, (b) 100 ohms and 0.86, henry, (c) 200 ohms and 1.0 henry, (d) 100 ohms and 0.93, henry, 34. An LCR series circuit with 100  resistance is, connected to an AC source of 200 V and angular, frequency 300 radians per second. When only the, capacitance is removed, the current lags behind the, voltage by 60º. When only the inductance is removed, the, current leads the voltage by 60º. Then the current and, power dissipated in LCR circuit are respectively, (a) 1A, 200 watt, (b) 1A, 400 watt, (c) 2A, 200 watt, (d) 2A, 400 watt, 35. In a series resonant LCR circuit, if L is increased by, 25% and C is decreased by 20%, then the resonant, frequency will, (a) Increase by 10%, (b) Decrease by 10%, (c) Remain unchanged, (d) Increase by 2.5 %, 36. An ac source of angular frequency  is fed across a, resistor R and a capacitor C in series. The current, registered is I. If now the frequency of source is changed, to /3 (but maintaining the same voltage), the current in, the circuit is found to be halved. The ratio of reactance to, resistance at the original frequency  will be., (a), , 3, , (b), , 5, , 5, 3, , (c), , 3, , 40. An alternating voltage given by V = 140 sin 314 t is, connected across a pure resistor of 50 the rms current, through the resistor is, (a) 1.98 A, (b) 5.63 A, (c) 8.43 A, (d) 2.39, A, 41. To reduce the resonant frequency in an LCR series, circuit with a generator, (a) The generator frequency should be reduced., (b) Another capacitor should be added in parallel to the, first., (c) The iron core of the inductor should be removed., (d) Dielectric in the capacitor should be removed., 42. In the case of an inductor, , , 2, , (b) Voltage leads the current by, 2, , (c) Voltage leads the current by, 3, , (d) Voltage leads the current by, 4, (a) Voltage lags the current by, , 43. In LCR- circuit if resistance increases, quality factor, (a) Increases finitely, (d) Decreases finitely, (c) Remains constant, (d) None of these, 44. The Q factor of a series LCR circuit with L = 2 H, C=, 32 F and R= 10  is, (a) 15, (b) 20, (c) 25, (d) 30, 45. Quality factor and power factor both have the, dimensions of, (a) Time, (b) Frequency, (c) Work, (d), Angle, , (d), , 5, , 5, 3, 37. In a series LCR circuit the voltage across an inductor,, capacitor and resistor are 20V,20V and 40V respectively, The phase difference between the applied voltage and the, current in the circuit is, (a) 30, , 0, , (b) 45, , 0, , (c) 60, , 0, , (d) 0, , 0, , 38. The r.m.s. value of the alternating e.m.f. E = (8 sin t +, 6 sin 2 t) V is, (a) 7.05 V, (b) 14.14 V, (c) 10 V, (d) 20 V, 39. A sinusoidal voltage Vosint is applied across a series, combination of resistance R and inductor L. The, amplitude of the current in the circuit is, (a), , (c), , Vo, , (b), , R 2   2 L2, Vo, R 2   2 L2, , sint, , Vo, R 2   2 L2, , (d) Vo/R, , 46.The average power loss in a series L-C-R circuit is, (a), , E o Io, 2, , (b), , 1 , , E o I o  L , , C , , 2R

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(c), , E o Io R, 1 , , 2 l , , C , , , (d), , Eo I o R, 2, 2, , , 1 , 2,  R ,  L , C , , , , 1/ 2, , 31. A transformer converts 220 V to 11 V. If the current, in the primary coil is 5A and that in the secondary, coil is 90A, then the efficiency of transformer will be, (a) 20%, (b) 100%, (c) 90%, (d) 150%, 32. In a transformer the voltage is stepped up from 220 V, rotational 440 V. If the currents in the primary was, 1.0 ampere, that in the secondary should be, (a) 1A, (b) between 0.5A and 1A, (c) 0.5A, (d) more than 1A., 33. The transformer is a device based on the, phenomenon of, (a) selfinduction, (b) electric discharge, (c) mutual induction, (d)Production of electromagnetic waves., 34. The core of transformer and other electric devices is, laminated to, (a) minimise eddy current losses, (b) increase the saturation level of core, (c) increase magnetic field, (d) decrease in retentivity of core, 35. Electric power is transmitted over long distance, through conducting wires at high voltage because, (a) it reduces the possibility of field of wire, (b) this entails less power losses, (c) a.c. generator produces electric power at very, high voltages, (d) a.c. signal of high voltage travels faster., 36. In an a.c. circuit the voltage applied is E = E0 sin ωt., The resulting current in the circuit is I =, , , , , I0sin  t , , 2., , 5., ,  . The power consumption in the, 2, , 2 E0I0 (b) E I, , 0 0, , 2, , (c) P = 0, , (d) P =, , A bulb is rated at 100 V, 100 W, it can be treated as a, resistor. Find out the inductance of an inductor (called, choke coil) that should be connected in series with the, bulb to operate the bulb at its rated power with the help of, an ac source of 200V and 50 Hz., , (a), , , , , 3, , H, , E0 I 0, 2, , 37. In an AC generator, a coil with N turns, all of the, same area A and total resistance R, rotates with, frequency ω in a magnetic field B. The maximum, value of emf generated in the coil is, (a) N.A.B.R.ω, (b) N.A.B., (c) N.A.B.R., (d) N.A.B.ω, 38. In a series resonant LCR circuit, the voltage across R, is 100 volts and R= 1kΩ with C = 2μF. The resonant, frequency ω is 200 rad/s. At resonance the voltage, across L is, (a) 2.5x10-2 V, (b) 40 V, (c) 250V, (d) 4x10-3V, 39. A circuit has a resistance of 12 ohm and an, impedance of 15 ohm, The power factor of the circuit, will be, (a) 0.4, (b) 0.8, (c) 0.125, (d) 1.25, 40. The phase difference between the alternating current, and emf is π/2. Which of the following cannot be the, constituent of the circuit?, (a) R, L (b) C alone (c) L alone (d) L,C, , 6., , (b) 100 H, , 2, H, , , (c), , (d), , 3, H, , A transformer is used to light a 100 Wand 110 V lamp, from a 220 V mains. If the main current is 0.5 A. The, efficiency of the transformer is approximately-, , (a) 30%, (d) 10%, , circuit is given by, (a) P =, , 41. The self inductance of the motor of an electric fan is, 10H.In order io impart maximum power at 50 Hz, it, should be connected to a capacitance of, (a) 8μF, (b) 4μF ( c) 2μF, (d) 1μF, 42. The power factor of an AC circuit having resistance, (R) and inductance (L) connected in series and an, angular velocity ω is, (a) R/ωL, (b) R/(R2 +ω2 L2 )1/2, (c) ω L/R, (d) R/(R2-ω2L2)1/2, 43. In a transformer, number of turns in the primary coil, are 140 and that in the secondary coil are 280. If, current in primary coil is 4, then that in the secondary, coil is, (a) 4A, (b) 2A, (c) 6A, (d) 10A., 44. The core of any transformer is laminated so as to, (a) reduce the energy loss due to eddy currents, (b) make it light weight, (c) make it robust and strong, (d) increase the secondary voltage, 45. In a LCR circuit capacitance is changed from C to, 2C. For the resonant frequency to remain unchanged,, the inductance should be changed from L to, (a) L/2, (b) 2L, (c) 4L, (d) L/4, , (b) 50%, , (c) 90%, , An ideal transformer has 500 and 5000 turns in primary, and secondary windings respectively. If the primary, voltage is connected to a 6V battery then the secondary, voltage is, , (a) 0, 6.0 V, , (b) 60V, , (c) 0.6 V, , (d), , 18., , A transformer is used to light 140W,24 V lamp form a, 240 V ac mains. If the main current is 0.7 A, the efficiency, of the transformer is, (a) 63.8%, (b) 74%, (c) 83.3%, (d) 48%, 19. A 60 W load is connected to the secondary of an ideal, transformer whose primary draws line voltage. If a current, of 0.54 A flows in the load, the current in the primary coil, is, (a) 0.27 mA (b) 2.7 Ma, (c) 0.27 A, (d) 10 A, 20., , An inductor of reactance 1 and a resistor of 2 are, connected in series to the terminals of a 6 V (rms) ac, source. The power dissipated in the circuit is, , (a) 8 W, 18 W, 26., , (b) 12 W, , (c) 14.4 W, , In an ac circuit, V and i are given by, , (d)

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, , V  100 sin(100t ) volts, and i  100 sin100t   mA Th, 3, , e power dissipated in circuit is, , (a) 10 4 watt (b) 10 watt, 5 watt, 47., , (c) 2.5 watt, , (d), , A step down transformer is connected to main supply, 200V to operate a 6V, 30W bulb. The current in primary is, , (a) 3 amp, 0.15 amp, , (b) 1.5 amp, , (c) 0.3 amp, , (d), , 48. A light bulb is rated at 100 W for a 220 V ac supply., The resistance of the bulb is, , (a) 284 , 584 , , (b) 384 , , (c) 484 , , (d), , 49. The loss of energy in the form of heat in the iron core, of a transformer is, (a) Iron loss, (b) Copper loss, (c) Mechanical loss, (d) None of these, 50. In a transformer the transformation ratio is 0.3.If 220 V, ac is fed to the primary, then the voltage across the, secondary is:, (a) 44 V, (b) 55 V, (c) 60 V, (d) 66 V, 51. Quantity that remains unchanged in a transformer is:, , (a) Voltage, (c) Frequency, these, , (b) Current, (d) None, , of, , 52. The line that draws power supply to your house from, street has, , (a) 220 2V average voltage., (b) 220 V average voltage., (c) Voltage and current out of phase by  / 2, (d) Voltage and current possibly differing in, , phase  such that |  | ., 2, 53. In which of the following circuits the maximum power, dissipation is observed?, , (a) Pure capacitive circuit, (b), Pure, inductive circuit, (c) Pure resistive circuit, (d) None of, these, 54. About 6% of power of a 100 W light bulb is, converted to visible radiation. The average in, intensity of visible radiation at a distance of 8 m, is (Assume) that the radiation is emitted, isotropically and neglect reflection., (a) 3.5  10 3 Wm 2, (b) 5.1 10 3 Wm 2, 3, , 2, , 3, , 2, , (c) 7.2  10 Wm, (d) 2.3  10 Wm, 55. The amplitude on an electromagnetic wave in, vacuum is doubled with not other changes made, to the wave. As a result of this doubling of the, amplitude, which of the following statement is, correct ?, (a) The speed of wave propagation changes only, (b) The frequency of the wave changes only, (c) The wavelength of the wave changes only, (d) None of these., , 56. An electromagnetic wave is propagating along, x-axis. At x =1m and t= 10s, its electric vector, , | E | 6V/ m then the magnitude of its magnetic, vector is, (a) 2  10 8 T, (b) 3  10 7 T, (c) 6  10 8 T, (d) 5  10 7 T, 57. The refractive index and permeability of a, medium are 1.5 and 5× 10 7 H m 1 respectively., The relative permittivity of the medium is, nearly:, (a) 25, (b) 15, (c) 10, (d) 6, 58. The rms value of the electric field of the light, coming from the sum is 720 N c 1 .The average, total energy density of the electromagnetic, wave is :, (a) 3.3  10 3 J m 3, (b) 4.58  10 6 J m 3, (c) 6.37  10 9 J m 3, , (d), , 81.35  10 12 J m 3, 59. Light with an energy flux of 18W cm 2 falls, on a non-reflecting surface at normal incidence., If the surface has an area of 20 cm 2 , the average, force exerted on the surface during a 30 minute, time span is :, (a) 2.1 10 6 N, (b) 1.2  10 6 N, (c) 2.1 10 6 N, (d) 1.2  10 6 N, 60. The electric fields part of an electromagnetic, wave in a medium is represented by E x  0,, E y  2.5, , , N, rad  ,  2 rad  , cos  2  10 6, t     10, x E z  0, The, C, m  , s  , , , wave is, (a) Moving along x direction with frequency, 10 6 Hz and wavelength 100 m, (b) Moving along x direction with frequency, 10 6 Hz and wavelength 200m, (c) Moving along -x direction with frequency, , 10 6 Hz and wavelength 200m, (d) Moving along y direction with frequency, , 2  10 6 Hz and wavelength 200m, 61. An electromagnetic radiation of wavelength , has the same momentum as an electron moving, with a speed 2 × 105ms–1 –, (a)  = 2.64 nm, (b)  = 1.64 nm, (c)  = 3.64 nm, (d)  = 4.64 nm, 62. Which one of the following is not, electromagnetic in nature –, (a) X-rays, (b) Gamma rays, (c) Cathode rays, (d) Infrared rays

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63. If a variable frequency ac source is connected, to a capacitor then with decreased in frequency, the displacement current will :, (a) Increase, (b) Decrease, (c) Remains constant, (d) First decrease, then increase, 64. Displacement current goes through the gap, between the plates of a capacitor when the, charge on the capacitor :, (a) Is changing with time, (b) Decreases, (c) Does not change, (d) Decreases, to zero, 65. A radio can tune to any station in 7.5 MHz to, 12 MHz band. The corresponding wavelength, band is :, (a) 40 m to 25 m, (b) 30 m to 25 m, (c) 25 m to 10 m, (d) 10 m to 5 m, 66. An electromagnetic, wave of frequency,   3MHz passes from vacuum into a dielectric, medium with permittivity  =4 ,Then :, (a) Wavelength and frequency both become half., (b) Wavelength is doubled and frequency, remains unchanged, (c) Wavelength and frequency both remain, unchanged., (d) Wavelength is halved and frequency remains, unchanged., 67. Which one of the following is the property of a, monochromatic, plane electromagnetic wave in, free space?, (a) Electric and magnetic fields have a phase, , difference of, 2, (b) The energy contribution of both electric and, magnetic fields are equal, (c) The direction of propagation is in the,  , direction of B  E, (d) The pressure exerted by the wave is the, product of its speed and energy density, 68. Which of the following rays is not an, electromagnetic wave?, (a) X-rays, (b) Y-rays, (c)  -rays, (d), Heat rays, 69. Which waves are used in sonography?, (a) Microwaves, (b) Infrared rays, (c) Radio waves, (d) Ultrasonic, 70. The ultra high frequency band of radiowaves, in electromagnetic electromagnetic wave is, used as in, , (a) Television waves, (b) Cellular phone communication, (c) Commercial FM radio, (d) Both (a) and(c), 71. A. Wavelength of microwaves is greater than, that of ultraviolet rays., B. The wavelength of infrared rays is lesser than, the ultraviolet rays., C. The wavelength of microwaves is lesser than, the that of infrared rays, D. Gamma ray has shortest wavelength in the, electromagnetic spectrum, Choose the correct option from the given, options., (a) A and B are true, (b) B and C are, true, (c) C and D are true, (d) A and D are true, 72. A microwaves and an ultrasonic sound wave, have the same wavelength. Their frequencies, are in the ratio a(approximately), (a) 10 2, (b) 104, (c) 10 6, (d), 10 8, 73. One require 11eV of energy to dissociate a, carbon monoxide molecule into carbon and, oxygen atoms. The minimum frequency of the, appropriate electromagnetic radiations to, achieve the dissociation lies in, (a) Visible region., (b) Infrared region., (c) Ultraviolet region., (d) Microwave region, , By: Praveen Gupta