**Points :**series circuit multiple choice questions and answers, electrical objective type question answers, mcqs Series Circuit 1. The power factor of a d.c. circuit is …..

(i) 0

(ii)

**1**

(iii) -1

(iv) none of above

2. For greater exactness, value of Ф (i.e. phase angle) should be resolute as of ……

(i) cos Ф

(ii) sin Ф

(iii)

**tan Ф**

(iv) sec Ф

3. The power factor of an a.c. circuit s known by ……

(i) X

_{L}/R

(ii) Z/R

(iii) R/X

_{L}

(iv)

**R/Z**

4. As power factor of a circuit is amplified, ..............

(i)

**reactive power is decreased**

(ii) active power is decreased

(iii) reactive power is increased

(iv) both active and reactive powers are enlarged.

5. In an R-L series circuit, R = 10 Ω and X

_{L}= 10 Ω. The phase angle among applied voltage and circuit current is

(i)

**45°**

(ii) 30°

(iii) 60°

(iv) 36.8°

6. Impedance of an a.c. circuit is a ………

(i) phasor

(ii) vector quantity

(iii)

**scalar quantity**

(iv) none of above

7. An inductive circuit draws a line current of 10A. If the reactive section of line current is 6 A, then power factor of circuit is ……….

(i) 0.6 Lagging

(ii)

**0.8 lagging**

(iii) 0.5 lagging

(iv) none of above

8. An R-L series a.c. circuit has 15 V across resistor and 20 V across the inductor. The supply voltage is ………

(i) 35V

(ii) 5V

(iii)

**25V**

(iv) 12V

9. The active and apparent powers of an a.c. circuit are equivalent in magnitude. The circuit power factor is ……

(i) 0.707

(ii) 0.5

(iii) 0.8

(iv)

**1**

10. If lagging reactive power of an a.c. circuit increases, power factor of circuit

(i) is amplified

(ii)

**is decreased**

(iii) remains unchanged

(iv) none of the above

11. In an R-L series circuit, line current ……..

(i) leads apply voltage

(ii)

**lags behind applied voltage**

(iii) is in phase by applied voltage

(iv) none of above

12. The active and reactive components of line current of an inductive circuit are equivalent. The power factor of the circuit is.

(i) 1

(ii)

**0707 lagging**

(iii) 0.5 lagging

(iv) 0.866 Lagging

13. In an R-L series circuit, two sides of the impedance triangle that type phase angle are ………..

(i) R and X

_{L}

(ii)

**R and Z**

(iii) Z and X

_{L}

(iv) none of above

14. In an R-L series circuit, phase difference Ф among applied voltage and circuit current will amplify if

(i)

**X**

_{L}is increased(ii) R is amplified

(iii) X

_{L}is decrease

(iv) supply frequency is decrease

15. The active and reactive powers of an inductive circuit are 60 W and 80 VAR respectively. The power factor of the circuit is ………..

(i) 0.8 lagging

(ii) 0.75 lagging

(iii)

**0.6 lagging**

(iv) 0.5 lagging

16. A wattmeter indicate ………. power.

(i)

**active**

(ii) reactive

(iii) apparent

(iv) none of the above

17. An R-L.C series circuit is linked to a 200 V a.c. source. If Q factor of coil is 10, then voltage crossways Cat resonance is ………

(i) 200 V

(ii)

**2000 V**

(iii) 20 V

(iv) 210 V

18. A 200 V, 50 Hz inductive circuit takes a current of 10A, lagging 30°. The inductive reactance of circuit is ……….

(i) 20 Ω

(ii)

**10 Ω**

(iii) 17.32 Ω

(iv) 16 Ω

19. A low power factor of circuit means that it will ………

(i) draw extra active power

(ii) draw less line current

(iii)

**draw more reactive power**

(iv) cause less voltage drop in line

20. At parallel resonance …………

(i) circuit impedance is minimum

(ii) power factor is zero

(iii) line current is maximum

(iv)

**power factor is unity**

21. An a.c. series circuit has R = 6Ω, X

_{L}=20Ω and X

_{C}= 12 Ω. Circuit power factor will be ………

(i) 08 lagging

(ii) 0.5 leading

(iii)

**06 lagging**

(iv) 06 leading

22. Reactive power in an a.c. circuit is ……….

(i) measured by a wattmeter

(ii) the functional power

(iii) consumed in the circuit

(iv)

**a liability on the circuit**

23. A circuit while connected to 200 V mains takes a current of 20 A. leading voltage through one-twelfth of time period. The circuit resistance is ……….

(i) 10 Ω

(ii)

**8.66 Ω**

(iii) 20 Ω

(iv) 17.32 Ω

24. An a.c. system supplies an obvious power of 10 kVA to a circuit, reactive power being 6 kVAR. The power factor of circuit is

(i)

**0.8**

(ii) 0-6

(iii) 0.75

(iv) none of above

25. At series resonance, …………….

(i) circuit impedance is extremely large

(ii) circuit power factor is minimum

(Iii) voltage across L or C is zero

(iv)

**circuit power factor is unity**

26. A coil is supplied by 200 V and takes a current of 2A at 45° lagging. The Q of coil is ……..

(i) 100

(ii) 25

(iii) 10

(iv)

**1**

27. With increase in frequency of a.c., the impedance of R-L-C series circuit

(i) increases

(ii) decreases

(iii) remains constant

(iv)

**first decreases, becomes minimum and then increases**

28. In an R-C series circuit, X

_{c}= R. The phase angle among apply voltage and circuit current is ……

(i) 30°

(ii)

**45°**

(iii) 60°

(iv) 90°

29. The dynamic impedance of a parallel resonant circuit is 1 M Ω. If C = 1μF and R = 1Ω, then value of L is ………..

(i)

**1H**

(ii) 10

^{12}H

(iii) 10

^{-12}H

(iv) none of the above

30. The Q factor of a coil is …….. resistance of coil.

(i)

**inversely proportional to**

(ii) directly proportional to

(iii) independent of

(iv) none of above

31. A voltage of 230 V is apply across a series a.c circuit of X

_{C}=25Ω, R = 15Ω and XL = 10 Ω. The phase angle among apply voltage and circuit current is ………

(i) zero

(ii) 30°

(iii) 60°

(iv)

**450**

32. As supply frequency is less than resonant frequency in a parallel a.c. circuit, then circuit is

(i) resistive

(ii) capacitive

(iii)

**inductive**

(iv) none of above

33. The impedance of an R-C series circuit is 100 Ω. If circuit current leads theoretical voltage by 45° then capacitive reactance is ……….

(i)

**70.7 Ω**

(ii) 141.42 Ω

(iii) 100 Ω

(iv) 50 Ω

34. When supply rate is more than resonant frequency in a similar a.c. circuit, then circuit is ………..

(i) resistive

(ii)

**capacitive**

(iii) inductive

(iv) none of the above

35. A stable current of 20 A flows during a coil of inductance 0.03 H as connected to a 200 V d.c. supply. When coil is linked to 200 V, 50 Hz supply, the impedance of circuit is

(i) 10 Ω

(ii) 5.6 Ω

(iii) 23.38 Ω

(iv)

**13.73 Ω**

36. If in an R-L-C series circuit, rate is lower the resonant regularity, then

(i) X

_{C}=X

_{L}

(ii) X

_{C}C

(iii)

**X**

_{C}>X_{C}(iv) none of the above

37. A pure inductor is connected to a variable frequency a.c. source. The graph among inductive reactance (X

_{L}) and frequency (f) will be

(i) straight line parallel to f-axis

(ii) straight line parallel to X

_{L}- axis

(iii)

**straight line passing through origin**

(iv) hyperbola

38. At series resonance, voltage across L or is ..........

(i) equal to apply voltage

(ii) less than apply voltage

(iii)

**much more than applied voltage**

(iv) equal to voltage across R

39. A series resonant circuit magnify ……….

(i)

**voltage**

(ii) current

(iii) both voltage & current

(iv) none of the above

40. In an a.c. circuit containing an inductor and a capacitor in series, current is create to be utmost when the value of inductance is 0.5 H and capacitance is 0.2 μF. The rate of input a.c. voltage is about

(i) 400Hz

(ii) 800Hz

(iii)

**500 Hz**

(iv) 1200 Hz

41. Dynamic impedance of a parallel tuned circuit is ………

(i)

**L/CR**

(ii) RL/C

(iii) L/C

(iv) R/L

42. A parallel resonant circuit magnifies ………

(i)

**current**

(ii) voltage

(iii) both voltage & current

(iv) none of above

43 A Lamp consume 25% of peak power in an ac. circuit. What is phase dissimilarity among the applied voltage and circuit current?

(i) π/6

(ii)

**π/3**

(iii) π/4

(iv) π/2

44. A resistance of 1 Ω, an inductance of 1 H and a capacitance of 1 F are linked in series and the line current is I A. The energy consumed in 1 hour is

(i)

**3600 J**

(ii) 1200 J

(iii) 1600 J

(iv) 600 J

45. A coil as connected to an a.c. supply of 200 V, 50 Hz takes 2 A. The power consumed is 200 W. The circuit power factor is

(i)

**1**

(ii)2

(iii) 0.5

(iv) none of above

46. A coil takes obvious and reactive powers of 100 VA and 80 VAR in that order. The Q factor of coil is ……….

(i)

**1.33**

(ii) 8

(iii) 10

(iv) none of the above

47. A choke coil is joined to 200 V. 50 Hz a.c. mains and takes 10 A. If choke coil takes 10 A on 100 V d.c. supply, the power factor of choke coil is

(i) 1

(ii) 0

(iii)

**0.5**

(iv) 0.2

48. Wattless current is said to flow as phase angle between voltage and currents is

(i)

**90°**

(ii) 0°

(iii) 60°

(iv) 180°

49. In a circuit element, the p.d. is higher than applied voltage of source. That will be

(i)

**an a.c. circuit**

(ii) an a.c. circuit

(iii) an a.c. or a d.c. circuit

(iv) neither a.c. nor d.c. circuit

50. A resistor and an inductor are attached in series to 220 V ac. supply. As measured by a.c. voltmeter, the potential difference across the resistor is 132 V. The potential difference crossways the inductor is

(i) 88V

(ii)

**176V**

(iii) 352V

(iv) cannot be predicted

51. In R..L.C series a.c. circuit, current

(i) is constantly in phase by applied voltage

(ii) always lags behind applied voltage

(iii) always leads applied voltage

(iv)

**none of above**

52. A pure capacitor is linked to a variable frequency a.c. source. The graph among capacitive reactance (X

_{C}) and frequency (F) will be

(i) a straight line passing through origin

(ii) a straight line parallel to f-axis

(iii) a straight tine parallel to X

_{C}-axis

(iv)

**a hyperbola**

53. An R-L-C series resonant circuit has a Q of 50 and source voltage of 5 V. The voltage V

_{C}crossways the capacitor is

(i) 10V

(ii)

**250V**

(iii) 125V

(iv) 500V

54. if Q of a circuit increases its BW

(i)

**decreases**

(iii) remains unchanged

(iv) none of above

(ii) increases

55. An a.c. source is in series by R and L. If the respective potential drops are 200 V and 150 V, the applied voltage is

(i) 125 V

(ii)

**350 V**

(iii) 200 V

(iv) 250 V

56. Power factor of a circuit can be better through the use of

(i) choke coil

(ii)

**capacitor**

(iii) induction motor

(iv) none of above

57. A 120 V.50 Hz source is linked to a circuit. If the circuit current is 3 A and power consumed is 108 W, the circuit resistance is

(i) 24Ω

(ii)

**12Ω**

(iii) 36Ω

(iv) cannot be predicted

58. The power supplied when a 120 V. 60 Hz source is connected to 33 μF capacitor is

(i) 122 VAR

(ii)

**179 VAR**

(iii) 211 VAR

(iv) 312 VAR

59. A resistor R is connected crossways a variable frequency a.c. source. The graph among R and frequency (f) will be a straight line

(i) passing through the origin

(ii)

**parallel to frequency axis**

(iii) parallel to R axis

(iv) inclined at some angle to R axis

60. In the over question, what is the true power supplied to circuit?

(i) 9W

(ii) 18W

(iii)

**4.5W**

(iv) 36.8 V

61. A series LC circuit is resonant at 150 kHz and has a Q of 50. What is the bandwidth?

(i)

**3kHz**

(ii) 4kHz

(iii) 6 kHz

(iv) 8 kHz

62. The current taken from a 230V,50Hz supply is measured as 10 A with a lagging p.f. of 0.7. A capacitor is connector in parallel by the load. The true power.

(i) increases

(ii) decreases

(iii)

**remains unchanged**

(iv) cannot be predicted

63. The capacitance of a capacitor which will allow 50 V. 10 W lamp to run as connected in series by an a.c. source of 220 V 50 Hz is about

(i) 30μF

(ii)

**3μF**

(iii) 300μF

(iv) 0.3μF

64. In R-L-C series resonant circuit R = 16 Ω L = 20 mH and C = 0.01 μF. If the apply voltage is 4V, voltage V

_{L}across inductor is

(i) 312.5 V

(ii) 225.6 V

(iii) 115.4 V

(iv)

**353.5 V**

65. A coil has an inductance of 0.7 H and is attached in series by a resistance of 220 Ω When n alternating voltage of 220 V. 50 Hz is apply to it, the wattless section of current is

(i) 1.5 A

(ii) 0.7 A

(iii) 7 A

(iv)

**0.5 A**

66. In R-L-C series a.c. circuit, the inductive reactance is equal to capacitive reactance. The phase angle among applied voltage and circuit current is

(i)

**0°**

(ii) 90°

(iii) 45°

(iv) 90°

67. The current in a circuit is wattless if

(i) inductance in circuit is zero

(ii)

**resistance in the circuit is zero**

(iii) current is alternating

(iv) resistance and inductance are both zero

68. The power supplied when a 120 V. 60 Hz source is linked to 50 mH inductor is

(i) 500 VAR

(ii) 430 VAR

(iii)

**766 VAR**

(iv) 336 VAR

69. A 60% lagging power factor implies that the load is

(i)

**inductive**

(ii) capacitive

(iii) inductive or capacitive

(iv) resistive

70. In above question the circuit p.f. might become

(i) 0.9 lagging

(ii) 085 lagging

(iii) 08 lagging

(iv)

**06 lagging**

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