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Prepared by: R.RAJENDRAN, M.A., M.Sc., M.Ed., N.INGARAN, M.Sc., M.Phil.,M.Ed., 12 TH STANDARD PHYSICS Electro magnetic induction and Alternating currents

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01. Lenz law is in accordance with the law of conservation of ……………………… a) momentum b) energy c) voltage d) current CHOOSE THE CORRECT ANSWER

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02. The self inductance of a straight conductor is …………………… a) infinity b) zero c) maximum d) minimum CHOOSE THE CORRECT ANSWER

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03. The unit henry can also be written as …………………… a) H b) A c) V s A -1 d) m / s CHOOSE THE CORRECT ANSWER

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04. Transformer works on ………………… currents only. a) direct b) alternating c) both direct and alternating d) steady CHOOSE THE CORRECT ANSWER

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05. The part of the AC generator that passes the current from the coil to the external circuit is a) armature b) slip rings c) field magnet d) brushes CHOOSE THE CORRECT ANSWER

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06. The number of magnetic lines of forces crossing unit area in a magnetic field is magnetic ………………… a) flux b) induction c) permeability d) radiation CHOOSE THE CORRECT ANSWER

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07. Electromagnetic induction was discovered by ………………. a) Lenz b) Hertz c) Michael Faraday d) Oersted CHOOSE THE CORRECT ANSWER

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08. Fleming’s right hand rule is also called as ………………… rule. a) cork screw b) thumb c) end d) generator CHOOSE THE CORRECT ANSWER

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09. The unit of self inductance is …………………... a) H b) A c) V s A -1 d) m / s CHOOSE THE CORRECT ANSWER

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10. The energy stored in an inductor is given by E = ………………. a) ½ L 2 I o b) L I o 2 c) L / I o 2 d) ½ L I o 2 CHOOSE THE CORRECT ANSWER

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11. The equation for the mutual induction of two long solenoids is M = ……………….. a) μ o N 1 N 2 A / l b) I / μ o N 1 N 2 A c) μ o N 1 N 2 A 2 / l d) N 1 N 2 A / l CHOOSE THE CORRECT ANSWER

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12. The induced emf by changing the area enclosed by a coil in a magnetic field is e = ………. a) EoSinωt b) – Blv c) - Bil d) – NBIA CHOOSE THE CORRECT ANSWER

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13. When the plane of a coil is perpendicular to a magnetic field, the induced emf is …………. a) maximum b) minimum c) zero d) infinity CHOOSE THE CORRECT ANSWER

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14. AC generator is a device used for converting the mechanical energy into ……….. a) sound energy b) heat energy c) electrical energy d) light energy CHOOSE THE CORRECT ANSWER

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15. If a number armature coils are used in the alternator, it is called as …………. Alternator. a) single phase b) two phase c) three phase d) poly phase CHOOSE THE CORRECT ANSWER

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16. Electro magnetic brakes use ……….. current. a) direct b) uni-directional c) eddy d) steady CHOOSE THE CORRECT ANSWER

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17. Transformer works on the ……………… principle. a) electro static induction b) Huygens’s c) electromagnetic induction d) self induction CHOOSE THE CORRECT ANSWER

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18. The ratio of the output power to the input power of a transformer is called ……………… a) velocity ratio b) mechanical advantage c) power loss d) efficiency CHOOSE THE CORRECT ANSWER

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19. Eddy current losses are minimized by using a core made of ……………… an alloy of steel. a) mumetal b) stelloy c) brass d) nichrome CHOOSE THE CORRECT ANSWER

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20. The frequency of AC used for domestic power in India is ………….. a) 0 Hz b) 50 Hz c) 100 Hz d) 400 Hz CHOOSE THE CORRECT ANSWER

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21. The average value of the AC over one complete cycle is ………….. a) 0 b) maximum c) minimum d) infinity CHOOSE THE CORRECT ANSWER

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22. The relation between Irms and Io is ……………… a) Irms = I o / √ 2 b) Irms = I o × √ 2 c) Irms = I o / 2 d) Irms = √ I o / 2 CHOOSE THE CORRECT ANSWER

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23. In an AC circuit containing R only, the phase difference between current and voltage is …… a) 0 b) π / 2 c) π / 4 d) π CHOOSE THE CORRECT ANSWER

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24. The inductive reactance X L is given by X L = …… a) L ω b) 1 / L ω c) L / ω d) ω / L CHOOSE THE CORRECT ANSWER

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25. A capacitor offers infinite resistance to ………… current. a) alternating b) direct c) varying d) sinusoidal CHOOSE THE CORRECT ANSWER

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26. In RLC circuit, the instantaneous current is given by I = …………………. a) I o Sin ( ω t ± φ ) b) I o tan ( ω t ± φ ) c) I o cos ( ω t ± φ ) d) I o / √ 2 CHOOSE THE CORRECT ANSWER

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27. The equation for Q factor is given by Q = ………….. a) 1 /2 π √ L /C ) b) R ( √ L /C ) c) 1 /R ( √ L /C ) d) 1 /R L C CHOOSE THE CORRECT ANSWER

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28. The average power consumed over a complete cycle is Pav = a) E rms I rms tan φ b) E rms I rms sin φ c) E rms I rms sec φ d) E rms I rms cos φ CHOOSE THE CORRECT ANSWER

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29. Choke coil is used to control the current in an ………… circuit. a) DC b) AC c) AC and DC d) steady CHOOSE THE CORRECT ANSWER

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30. Choke coils are used in ………….. tubes which work on alternating currents. a) filament b) oil c) fluorescent d) glass CHOOSE THE CORRECT ANSWER

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31. The reactance of an inductor is ……………… proportional to the frequency. a) first directly, then inversely b) first inversely, then directly c) directly d) inversely CHOOSE THE CORRECT ANSWER

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32. Shell type cores are used to minimize ………………… losses. a) eddy current b) power c) hysteresis d) flux CHOOSE THE CORRECT ANSWER

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33. The number of magnetic lines of forces crossing a closed area is called magnetic …………….. a) flux b) induction c) permeability d) radiation CHOOSE THE CORRECT ANSWER

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34. The selectivity or sharpness of a resonant circuit is measured by the …………… factor. a) safety b) power c) quality d) energy CHOOSE THE CORRECT ANSWER

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35. The ratio of the voltage across a coil or capacitor to the applied voltage is called as …………factor. a) safety b) quality c) power d) energy CHOOSE THE CORRECT ANSWER

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36. For normal frequencies, the Q factor lies between ……………... a) 1 and 10 b) 100 and 1000 c) 10 and 100 d) 0.1 and 10 CHOOSE THE CORRECT ANSWER

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37. For radio frequencies, air chokes are used. These chokes are called as ………… chokes. a) AF b) AF or RF c) R F or H F d) AF or HF CHOOSE THE CORRECT ANSWER

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38. Whenever there is a change in the magnetic flux linked with a closed circuit, an emf is induced in it. This phenomenon is called ………………….. a) electro static induction b) action of points c) electromagnetic induction d) self induction CHOOSE THE CORRECT ANSWER

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39. In Fleming’s right hand rule, the middle finger points the direction of the ………… a) motion of the conductor b) magnetic field c) induced current d) force CHOOSE THE CORRECT ANSWER

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40. The property of the coil which enables to produce an opposing induced emf in it when the current in the coil changes is called …………………… a) electro static induction b) self induction c) electromagnetic induction d) induction CHOOSE THE CORRECT ANSWER

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41. If two coils are wound on a soft iron core one over the other, the mutual induction is ……………… a) zero b) infinity c) minimum d) very large CHOOSE THE CORRECT ANSWER

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42. The induced emf is given by the equation e = …………… a) Eo sin ωt b) Eo cosωt c) Eo sec ωt d) Eo tan ωt CHOOSE THE CORRECT ANSWER

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43. In fans, …………….. motors are used. a) electro static induction b) self induction c) electromagnetic induction d) induction CHOOSE THE CORRECT ANSWER

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44. In step up transformers, the transformer ratio k is …………… than one. a) lesser b) greater c) smaller d) none CHOOSE THE CORRECT ANSWER

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45. A power of 11kW is transmitted at 5.5kV through a transmission line of 1 ohm. The power loss = ……… a) 4 W b) 40 W c) 0.4 W d) 400 W CHOOSE THE CORRECT ANSWER

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46. In an AC circuit containing C only, the phase difference between the current and the voltage is …………… a) 0 b) π / 2 c) π / 4 d) π CHOOSE THE CORRECT ANSWER

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47. In an LCR circuit, at resonance, the impedance is ……………. a) minimum b) maximum c) infinity d) zero CHOOSE THE CORRECT ANSWER

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48. The rms value of the AC is ………….. times the peak value of the alternating current. a) b) c) d) CHOOSE THE CORRECT ANSWER

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49. The direction of the eddy current can be noted by …………… a) Faraday’s laws b) Lenz’s law c) cork screw rule d) end rule CHOOSE THE CORRECT ANSWER

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50. In a three phase AC generator, the emf’s of the coils differ by ………………... a) 120 b) 180 c) 90 d) 0 CHOOSE THE CORRECT ANSWER

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51. Electromagnetic induction is not used in (a) transformer (b) room heater (c) AC generator (d) choke coil CHOOSE THE CORRECT ANSWER

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52. A coil of area of cross section 0.5 m2 with 10 turns is in a plane which is penpendicular to an uniform magnetic field of 0.2 Wb/m 2. The flux though the coil is (a) 100 Wb (b) 10 Wb (c) 1 Wb (d) zero CHOOSE THE CORRECT ANSWER

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53. Lenz’s law is in accordance with the law of (a) conservation of charges (b) conservation of flux (c) conservation of momentum (d) conservation of energy CHOOSE THE CORRECT ANSWER

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54. The self−inductance of a straight conductor is (a) zero (b) infinity (c) very large (d) very small CHOOSE THE CORRECT ANSWER

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55. The unit henry can also be written as (a) Vs A −1 (b) Wb A −1 (c) Ω s (d) all CHOOSE THE CORRECT ANSWER

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56. An emf of 12 V is induced when the current in the coil changes at the rate of 40 A S –1. The coefficient of self induction of the coil is (a) 0.3 H (b) H (c) 30 H (d) 4.8 H CHOOSE THE CORRECT ANSWER

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57. A DC of 5A produces the same heating effect as an AC of (a) 50 A rms current (b) 5 A peak current (c) 5A rms current (d) none of these CHOOSE THE CORRECT ANSWER

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58. Transformer works on (a) AC only (b) DC only (c) both AC and DC (d) AC more effectively than DC CHOOSE THE CORRECT ANSWER

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59. The part of the AC generator that passes the current from the coil to the external circuit is (a) field magnet (b) split rings (c) slip rings (d) brushes CHOOSE THE CORRECT ANSWER

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60. In an AC circuit the applied emf e = Eo sin (ωt + π/2) leads the current I = Io sin (ωt – π/2) by (a) π/2 (b) π/4 (c) π (d) 0 CHOOSE THE CORRECT ANSWER

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61. Which of the following cannot be stepped up in a transformer? (a) input current (b) input voltage (c) input power (d) all CHOOSE THE CORRECT ANSWER

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62. The power loss is less in transmission lines when (a) voltage is less but current is more (b) both voltage and current are more (c) voltage is more but current is less (d) both voltage and current are less CHOOSE THE CORRECT ANSWER

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63. Which of the following devices does not allow d.c. to pass through? (a) resistor (b) capacitor (c) inductor (d) all the above CHOOSE THE CORRECT ANSWER

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64. In an ac circuit (a) the average value of current is zero. (b) the average value of square of current is zero. (c) the average power dissipation is zero. (d) the rms current is 2 time of peak current. CHOOSE THE CORRECT ANSWER

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THE END

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