Controlling Speed Using Inductance MCQ [Free PDF] – Objective Question Answer for Controlling Speed Using Inductance Quiz

21. The slope of the V-I curve is 56.489°. Calculate the value of resistance. Assume the relationship between voltage and current is a straight line.

A. 1.5 Ω
B. 1.6 Ω
C. 2.5 Ω
D. 1.4 Ω

Answer: A

The slope of the V-I curve is resistance.

The slope given is 56.489° so R=tan(56.489°)=1.5 Ω.

The slope of the I-V curve is reciprocal to resistance. 

 

22. If induction motor air gap power is 28.63 KW and gross developed power is 18.8 KW, then rotor ohmic loss will be _________ KW.

A. 9.83
B. 10.55
C. 15.54
D. 4.74

Answer: A
Rotor ohmic losses are due to the resistance of armature windings. Net

input power to the rotor is equal to the sum of rotor ohmic losses and mechanically developed power. Rotor ohmic losses=Air gap power-Mechanical developed power

=28.63-18.8=9.83 KW. 

 

23. Calculate the value of inductive reactance if F=50 Hz and L=12 H.

A. 3768 Ω
B. 2578 Ω
C. 2477 Ω
D. 2456 Ω

Answer: A

Inductive reactance can be calculated using the relation

XL=2×3.14×f×L.

The value of inductive reactance is

XL=2×3.14×50×12=3768 Ω. 

 

24. Calculate the value of capacitive reactance if F=60 Hz and C=14 H.

A. 189.5 mΩ
B. 252.4 mΩ
C. 244.5 mΩ
D. 244.8 mΩ

Answer: A

Capacitive reactance can be calculated using the relation

Xc=1÷2×3.14×f×L.

The value of capacitive reactance is

Xc=1÷2×3.14×50×12=189.5 mΩ. 

 

25. Calculate the time period of the waveform v(t)=.6sin(.1πt+8π)+17cos(2πt+π)+ 4tan(.1πt).

A. 88 sec
B. 20 sec
C. 70 sec
D. 43 sec

Answer: B

The fundamental time period of the sine wave is 2π. The time period of v(t) is

L.C.M {20,1,20}=20 sec.

The time period is independent of phase shifting and time-shifting. 

 

26. Calculate the value of resistance if total heat dissipated is 78 W when 5 A current flows through it.

A. 3.12 Ω
B. 2.24 Ω
C. 1.45 Ω
D. 5.13 Ω

Answer: A

The resistor is a linear element. It only absorbs real power and dissipates it in the form of heat. The voltage and current are in the same phase in the case of the resistor so the angle between V & I is 0°.

R=P÷I2=3.12 Ω. 

 

27. The value of slip at the starting of an induction motor is ________

A. 0
B. 1
C. 2
D. 3

Answer: B

The maximum torque occurs when the slip value is equal to R2÷X2. At the starting, the rotor speed is equal to zero so the slip value is 1. 

 

28. The value of the slip of an induction motor during full load condition is ________

A. 0.99
B. .1
C. .8
D. 0

Answer: D

During full load conditions, the speed of the rotor is nearly synchronous speed. The value of the slip is nearly zero during full load conditions. 

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