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
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
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.
3. The unit of angular velocity in rad/s3.
A. True
B. False
Answer: B
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=Vmsin(ωt+α).
A. Vm÷2½
B. Vm÷2¼
C. Vm÷2¾
D. Vm÷3½
Answer: A
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.
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
Answer: C
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
Increasing turn-off time implies decreasing speed and the majority of carrier devices do not have any minority charge carrier storage so they have less turn-off time 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
A 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: Pin = 3000 W, Ia = 60 A, Ra = .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
Useful power is basically the shaft power developed by the motor that can be calculated using the formula
Psh = Pdev-(rotational losses)
Pdev = Pin-Ia2Ra = 3000-602(.4)=1560 W.
The useful power developed by the motor is
Psh = Pdev-(rotational losses)=1560 –(200+400)=960 W.
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
The sinusoidal waveform is generally expressed in the form of V=Vmsin(ωt+α)
where
Vm represents the peak value
ω represents angular frequency,
α represents a phase difference.
10. The axis along which no emf is produced in the armature conductors is called as ____________
A. Geometrical Neutral Axis (GNA.
B. Magnetic Neutral Axis (MNA.
C. Axis of rotation
D. Axis of revolution
Answer: B
The coil undergoing commutation must lie along the magnetic neutral axis so that no emf is induced and there is no sparking at the time of commutation.