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Monday, 23 November 2015

Alternating Current - Multiple Choice Questions

Alternating Current - Multiple Choice Questions Points : alternating current multiple choice questions and answers, electrical objective type question answers, mcqs 1. ......... will make a.c. voltage.
(i) Friction
(ii) Photoelectric effect
(iii) Thermal energy
(iv) Crystal

2. A coil is rotate in the even field of an 8-pole generator. In one revolution of coil, the number of cycles generate through the voltage is
(i) one
(ii) two
(iii) four
(iv) eight

3. In a.c. system, we make sinewave form because ______.
(i) it can be simply drawn
(ii) it produces least disturbance in electrical circuits
(iii) it is nature’s standard
(iv) other waves cannot be formed simply

4. ………… will work simply on d.c. supply
(i) Electric lamp
(ii) Refrigerator
(Iii) Heater
(iv) Electroplating

5. An alternating current is given by i = 10 sin 314 t. Measuring time from t = 0, the time taken through the current to reach +10 V for second time is ………
(i) 0.05 second
(ii) 0.1 second
(iii) 0.025 second
(iv) 0.02 second

6. The a.c. system is prefer to d.c. system as ………
(i) a.c. voltages can be simply changed in magnitude
(ii) dc. motors do not contain fine speed control
(iii) high-voltage a.c. transmission is less capable
(iv) d.c. voltage cannot be use for home appliances

7. An alternating voltage is given by v = 30 sin 314 t. The time in use by the voltage to reach —30V for the first time is ……….
(i) 0.02 second
(ii) 0.1 second
(iii) 003 second
(iv) 0.015 second

8. An alternating voltage is given by v = 20 sin 157 t. The frequency of alternating voltage is ………
(i) 50 Hz
(ii) 25 Hz
(iii) 100 Hz
(iv) 75 Hz

9. An alternating voltage is given through v = 100 sin 314 t volts. Its average charge will be ……….
(i) 70.7 V
(ii) 50 V
(iii) 63.7 V
(iv) 100 V

10. An alternating current whose average value is 1 A will create ………. 1 A d.c. under like conditions.
(i) less heat than
(ii) more heat than
(iii) the same heat as
(iv) none of the above

11. Alternating voltages and currents are expressed in r.m.s. values as
(i) they can be simply resolute
(ii) calculations become very simple
(iii) they give comparison with d.c.
(iv) none of the above

12. The area of a sinusoidal wave over a halfcycle is ………
(i) max. value +2
(ii) 2 x max. value
(iii) max. value + π
(iv) max. value + 2π

13. We have assign a frequency of 50 Hz to power system as it ……..
(i) can be simply obtain
(ii) gives best result when used for operating both Lights and machinery
(iii) Leads to simple calculations
(iv) none of the over

14. An alternating current is particular through i = 10 sin 314 t. The time taken to produce two cycles of current is ……..
(i) 0.02 second
(ii) 0.01 second
(iii) 0.04 second
(iv) 0.05 second

15. The r.m.s. value of sinusoidally unreliable current is ............ that of its standard value.
(i) more than
(ii) less than
(iii) same as
(iv) none of the above

16. A sine wave has a utmost value of 20 V. Its value at 135° is ……….
(i) 10 V
(ii) 14.14 V
(iii) 15 V
(iv) 5 V

17. The average value of sin θ over a whole cycle is .
(i) zero
(ii) +1
(iii) -1
(iv) 1/2

18. An a.c. generator having 10 poles and running at 600 r.p.m. will make an alternating voltage of frequency

(i) 25 Hz
(ii) 100 Hz
(iii 50 Hz
(iv) 200 Hz

19. An alternating voltage is given by v = 200 sin 314 t. Its r.m.s value will be ……..
(i) 100 V
(ii) 282.8 V
(iii) 141.4 V
(iv) 121.4 V

20. The form factor of a sinusoidal wave is ……….
(i) 1.414
(ii) 1.11
(iii) 2
(iv) 1.5

21. The average value of sin 2θ over a whole cycle is
(i) +1
(ii) -1
(iii) ½
(iv) zero

22. A 100 V peak a.c.is as effectual as ……… d.c.
(i) 100 V
(ii) 5O V
(iii) 70.7 V
(iv) none of the above

23. The peak factor of a half-wave rectified a.c. is ……..
(i) 1.57
(ii) 2
(iii) 1.11
(iv) 1.4142

24. Out of the following ........ wave is the peakiest.
(i) sinusoidal
(ii) square
(iii) rectangular
(iv) triangular

25. The peak factor of a sinewave form is ……..
(i) 1.11
(ii) 1.414
(iii) 2
(iv) 1.5

26. In a pure resistive circuit, the immediate voltage and current are given through:
v = 250 sin 3 14 t volts
I = 10 sin 3l4 amperes
The peak power in the circuit is ……….
(i) 1250W
(ii) 25W
(iii) 2500 W
(iv) 250 W

27. The form factor of a half-wave rectify a.c. is ………
(i) 2
(ii) 1.11
(iii) 1.414
(iv) 157

28. When 200 V sinucoidal peak-to-peak is attached across an a.c. voltmeter, it will examine
(i) 141.4 V
(ii) 50V
(iii) 70.7 V
(iv) none of the above

29. The form factor of a ............. wave is 1.
(i) sinusoidal
(ii) square
(iii) biangular
(iv) saw both

30. The inductive reactance of a circuit is ………… rate.
(i) directly proportional to
(ii) inversely proportional to
(iii) independent of
(iv) none of the above

31. The breakdown voltage of an insulation depends upon ........... value of alternating voltage.
(i) average
(ii) r.m.s.
(iii) peak
(iv) twice the r.m.s.

32. The standard value of a sinusoidal current is 100 A. Its r.m.s. value is ………
(i) 63.7 A
(ii) 70.7
(iii) 141.4 A
(iv) 111 A

33. Power absorbed in a pure inductive circuit is zero as ……….
(i) reactive component of current is zero.
(ii) active component of current is maximum
(iii) power factor of the circuit is zero
(iv) reactive and active apparatus of current cancel out

34. An alternating voltage or current is a …….
(i) scalar quantity
(ii) vector quantity
(iii) phasor
(iv) none of the above

35. The capacitive reactance of a circuit is ………… frequency.
(i) independent of
(ii) inversely proportional to
(iii) directly proportional to
(iv) none of the above

36. What is peak to-peak value for 120 V a.c..?
(i) 240 V
(ii) 480 V
(iii) 339 V
(iv) 391 V

37. In a pure resistive a.c. circuit, the rate of power curve is ……… that of the circuit frequency.
(i) half
(ii) twice
(iii) thrice
(iv) same as

38. A 500 V sine wave producer appears across a 10 k Ω resistor. What is immediate current in the resistor at a phase angle of 35°?
(i) 12.4 mA
(ii) 22.6 mA
(iii) 52 mA
(iv) 40.6 mA

39. The e.m.f. is given by e=8 sin ωt + 6 sin 2 ωt volts. The r.rn.s. value is
(i) 10.2 V
(ii) 12 V
(iii) 7.07 V
(iv) none of the above

40. The instantaneous value of 55 sin (2π x 16t) mA at t = 1/32 second is
(i) 0 mA
(ii) 5.08 mA
(iii) 12 mA
(iv)2.3 mA

41. Find average value of v (t) = 6 + 2 sin (2 π x 100 t) volts
(i) 6V
(ii) 12V
(iii) 94V
(iv) 16.3V

42. The ac current through a 20 μF capacitor is i (t) = 3 sin (800 t) A. What is peak voltage crossways the capacitor?
(i) 187.5 V (ii) 90.5 V
(iii) 118.4 V
(iv) 55.6 V

43. The effective value of 2A d.c current is
(i) 1 A
(ii) 4 A
(iii) 16 A
(iv) 2A

44. In the above question, average power in circuits is
(i) 2500 W
(ii) 250 W
(iii) 25 W
(iv) 1250 W

45. The average value of 2 A dc current is
(i) 1A
(ii) 4A
(iii) 2A
(iv) 3A

46. A current is made up of two components viz 3 A d.c. component and a.c. component given through i =4 sin ωt. The average value of current is
(i) 5K
(ii) 4A
(iii) 7A
(iv) 11A

47. A capacitor is a perfect insulator for
(i) alternating current
(ii) direct current
(iii) direct as well as alternating current
(iv) none of above

48. A hot wire ammeter reads 10 A in an a.c. circuit contain 10 Ω. The peak value of voltage crossways the resistor is
(i) 141.4 V
(ii) 282.8 V
(iii) 100 V
(iv) 400 V

49. The voltage across a 0.5 μF capacitor is v (t) = 16 sin (2 x103 t) V. The capacitive reactance of capacitor is
(i) 1.5 kΩ
(ii) 1 kΩ
(iii) 2.4 kΩ
(iv) 3.6kΩ

50. If angular speed of rotation of an armature of alternating current generator is double, then the induced e.m.f. will be
(i) twice
(ii) half
(iii) four times
(iv) no change

51. What is instantaneous output of a generator at 20 electrical degrees if its output is 170 V at 90 electrical degrees?
(i) 30 V
(ii) 58.1 V
(iii) 24.3 V
(iv) 42.6 V

52. An alternating current is converted to direct current by
(i) dynamo
(ii) transformer
(iii) rectifier
(iv) motor

53. A pure inductor is connected to an alternating voltage source. If equally the voltage and the frequency are double, the circuit current
(i) becomes double
(ii) is halved
(iii) becomes three times
(iv) no change

54. To what rate the resistance the above question be changed is average power dissolute in it must be abridged to 1 W ?
(i) 72 Ω
(ii) 36 Ω
(iii) 24 Ω
(iv) 108 Ω

55. A choke coil is a coil have
(i) low inductance and high resistance
(ii) low inductance and low resistance
(iii) high inductance and negligible resistance
(iv) high inductance and high resistance

56. A current of S mA flows in a resistanceless choke as of a 220 V alternating source. The energy extreme in the choke is
(i) 1000 J
(ii) 500 J
(iii) 4.4J
(iv) zero

57. The time period of direct current is
(i) infinite
(ii) zero
(iii) finite
(iv) cannot say

58. In an a.c. circuit, electrical energy is consumed in
(i) L
(ii) C
(iii) L and C
(iv) R

59. A 40 Ω electric heater is attached to a 200 V, 50 Hz supply. The peak value of electric current in the circuit is roughly
(i) 7A
(ii) 2.5A
(iii) 5 A
(iv) 10 A

60. A choke is prefer to a resistance for preventive current in an a.c. circuit as
(i) choke is cheap
(ii) there is no wastage of energy
(iii) current becomes wattless
(iv) current strength increases

61. If an alternating current of 50 Hz is flowing in a circuit, the current become zero
(i) 50 times
(ii) 25 times
(iii) 100 times
(iv) 200 times

62. In comparison to dc, transmission fatalities in a.c. are
(i) high
(ii) low
(iii) negligible
(iv) none of above

63. The inductive reactance of an inductor in a d.c. circuit is
(i) ωL
(ii) 1/ωL
(iii) zero
(iv) infinite

64. An air-core choke coil and an electric bulb are linked in series with a.c. mains. On introduce soft iron bar in the coil, the amount of light will
(i) fluctuate
(ii) remain unchanged
(iii) increase
(iv) decrease

65. An electric bulb rated at 220 V is attached to 220 V,5 Hz a.c. source. Then bulb
(i) does not glow
(ii) fuses
(iii) glows continuously
(iv) glows intermittently

66. An a.c. source is 120 V, 60 Hz. The value of voltage after 1/720 sec as of start is
(i) 84.8 V
(ii) 42.4 V
(iii) 244 V
(iv) 52.2 V

67. In above question, the circuit current will lead the apply voltage by
(i) 60°
(ii) 30°
(iii) 120°
(iv) 90°

68. An alternating current varies through complete one cycle in 1 μs. Its rate is
(i) 103Hz
(ii) 104 Hz
(iii) 106 Hz
(iv) none of above

69. An alternating current cannot be exact by a d.c. ammeter as
(i) a.c. in virtual
(ii) a.c. cannot pass through d.c. ammeter
(iii) average value of a.c. over one cycle is zero
(iv) none of above

70. The function of choke in a fluorescent tube is
(i) to decrease the current
(ii) to increase the current
(iii) to decrease the voltage shortly
(iv) to increase the voltage momentarily

71. Radio frequency choke is
(i) air-cored
(ii) iron-cored
(iii) air as well as iron-cored
(iv) none of above

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