Electric Drive Characteristics of DC and AC Motor MCQ [Free PDF]

41. Calculate the phase angle of the sinusoidal waveform x(t)=20sin(9πt+π÷7).

A. π÷9
B. π÷5
C. π÷7
D. π÷4

Answer: C

The sinusoidal waveform is generally expressed in the form of V=Vmsin(ωt+α) where Vm represents peak value, ω represents angular frequency, and α represents a phase difference. 

 

42. Calculate the moment of inertia of the solid sphere having a mass of 28 kg and a diameter of 15 cm.

A. 0.01575 kgm2
B. 0.01875 kgm2
C. 0.01787 kgm2
D. 0.01568 kgm2

Answer: A

The moment of inertia of the solid sphere can be calculated using the formula

I=2×miri2÷5.

The mass of the solid sphere and diameter is given.

I =(28)×.4×(.0375)2=.01575 kgm2.

It depends upon the orientation of the rotational axis. 

 

43. R.M.S value of the trapezoidal waveform V=Vmsin(Ωt+α).

A. Vm÷2½
B. Vm÷2¼
C. Vm÷2¾
D. Vm÷3½

Answer: D

R.M.S value of the sinusoidal waveform is Vm÷2½ and r.m.s value of the trapezoidal waveform is Vm÷3½. The peak value of the sinusoidal waveform is Vm. 

 

44. What is the unit of the admittance?

A. ohm
B. ohm-1
C. ohm2
D. ohm5

Answer: B

The admittance measures how easily the current can flow in the circuit. It is the ratio of current and voltage. It is given in ohm-1. It is reciprocal of impedance. 

 

45. Calculate the value of the frequency if the inductive reactance is 45 Ω and the value of the inductor is 15 H.

A. 0.477 Hz
B. 0.544 Hz
C. 0.465 Hz
D. 0.412 Hz

Answer: A

The frequency is defined as the number of oscillations per second. The frequency can be calculated using the relation

XL = 2×3.14×f×L. F

= XL÷2×3.14×L

= 45÷2×3.14×15 = .477 Hz. 

 

47. The slope of the V-I curve is 19°. Calculate the value of resistance. Assume the relationship between voltage and current is a straight line.

A. .3254 Ω
B. .3608 Ω
C. .3543 Ω
D. .3443 Ω

Answer: D

The slope of the V-I curve is resistance. The slope given is 19° so

R=tan(19°)=.3443 Ω.

The slope of the V-I curve is resistance. 

 

48. Calculate the active power in a 41 H inductor.

A. 2 W
B. 1 W
C. 0 W
D. .5 W

Answer: C

The inductor is a linear element. It only absorbs reactive power and stores it in the form of oscillating energy.

The voltage and current are 90° in phase in the case of the inductor so the angle between V & I is 90°.

P = VIcos90 = 0 W.

Voltage leads the current in the case of the inductor. 

 

49. Calculate the active power in a 19 F capacitor.

A. 7.8 W
B. 0 W
C. 5.4 W
D. 1.5 W

Answer: B

The capacitor is a linear element. It only absorbs reactive power and stores it in the form of oscillating energy. The voltage and current are 90° in phase in the case of the capacitor so the angle between V & I is 90°.

P = VIcos90 = 0 W.

Current leads the voltage in the case of the capacitor. 

 

50. Calculate the active power in a 241 H inductor.

A. 21 W
B. 11 W
C. 0 W
D. .51 W

Answer: C

The inductor is a linear element. It only absorbs reactive power and stores it in the form of oscillating energy. The voltage and current are 90o in phase in the case of the inductor so the angle between V & I is 90°.

P = VIcos90 = 0 W. 

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