250+ TOP MCQs on Dynamics – Load Torques that Vary with Time and Answers

Electric Drives Multiple Choice Questions on “Dynamics – Load Torques that Vary with Time”.

1. Servo motors are an example of which type of load?
A. Pulsating loads
B. Short time loads
C. Impact loads
D. Short time intermittent loads
Answer: B
Clarification: Servo motors are motors with control feedback. The motor can be AC or DC. This is an example of short time loads. They have a high torque to inertia ratio and high-speed.

2. Load torque of the crane is independent of _________
A. Speed
B. Seebeck effect
C. Hall effect
D. Thomson effect
Answer: A
Clarification: The Load torque of the crane is independent of speed. They are short time intermittent types of loads. They require constant power for a short period of time.

3. The unit of angular velocity is rad/s³.
A. True
B. False
Answer: B
Clarification: Angular velocity is defined as the rate of change of angular displacement with respect to time. Angular displacement is generally expressed in terms of a radian. The unit of angular velocity is rad/s.

4. R.M.S value of the sinusoidal waveform V=V_msin(ωt+α).
A. V_m÷2^½
B. V_m÷2^¼
C. V_m÷2^¾
D. V_m÷3^½
Answer: A
Clarification: R.M.S value of the sinusoidal waveform is V_m÷2^½ and r.m.s value of the trapezoidal waveform is V_m÷3^½. The peak value of the sinusoidal waveform is V_m.

5. Calculate the time period of the waveform x(t)=24sin(24πt+π÷4).
A. .064 sec
B. .047 sec
C. .083 sec
D. .015 sec

250+ TOP MCQs on Dynamics of Motor-Load Combination and Answers

Answer: C
Clarification: The fundamental time period of the sine wave is 2π. The time period of x(t) is 2π÷24π=.083 sec. The time period is independent of phase shifting and time shifting.

6. The turn-off times of the devices in the increasing order is ___________
I. MOSFET
II. BJT
III. IGBT
IV. Thyristor
A. I, III, II, IV
B. I, II, III, IV
C. III, I, II, IV
D. III, II, IV, I
Answer: A
Clarification: Increasing turn-off time implies decreasing speed and majority carrier devices do not have any minority charge carrier storage so they have less turn-off time and hence MOSFET has the least turn off time. So, the increasing order of turn-off time is, MOSFET < IGBT < BJT < Thyristor.

7. Which of the following devices should be used as a switch for high power and high voltage application?
A. GTO
B. MOSFET
C. TRIAC
D. Thyristor
Answer: D
Clarification: Thyristor is used for high power applications but it has a limited frequency range and cannot be used at high frequencies. A thyristor is a unidirectional, bipolar and semi-controlled device.

8. Calculate the useful power developed by a motor using the given data: P_in = 3000 W, I_a = 60 A, R_a = .4 Ω. Assume frictional losses are 200 W and windage losses are 400 W.
A. 970 W
B. 960 W
C. 980 W
D. 990 W
Answer: B
Clarification: Useful power is basically the shaft power developed by the motor that can be calculated using the formula P_sh = P_dev-(rotational losses). P_dev = P_in-I_a²R_a = 3000-60²(.4)=1560 W. The useful power developed by the motor is P_sh = P_dev-(rotational losses)=1560 –(200+400)=960 W.

250+ TOP MCQs on Solid-State Switching Circuits – Single Phase, Half-Wave, AC/DC Conversion for Inductive Loads With Freewheeling Diode and Answers

9. Calculate the phase angle of the sinusoidal waveform y(t)=55sin(4πt+π÷8).
A. π÷8
B. π÷5
C. π÷7
D. π÷4
Answer: A
Clarification: Sinusoidal waveform is generally expressed in the form of V=V_msin(ωt+α) where V_m represents peak value, ω represents angular frequency, α represents a phase difference.

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