Load Torques that Vary with Angle of Displacement of Shaft MCQ [Free PDF] – Objective Question Answer for Load Torques that Vary with Angle of Displacement of the Shaft Quiz
11. 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.
12. 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.
13. 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.
14. 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.
15. 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.
16. 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.
17. 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.
18. 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.
19. 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.
20. The generated e.m.f from 25-pole armature having 200 conductors driven at 10 rev/sec having flux per pole as 20 mWb, with two parallel paths is ___________
A. 400 V
B. 500 V
C. 200 V
D. 300 V
Answer: B
The generated can be calculated using the formula
Eb = Φ×Z×N×P÷60×A,
Where
Φ represents flux per pole
Z represents the total number of conductors
P represents the number of poles,
A represents the number of parallel paths
N represents speed in rpm
Eb = .02×25×200×600÷60×2= 500 V.
21. The unit of the flux is Weber.
A. True
B. False
Answer: A
Flux is the total amount of magnetic field lines passing through a given area. Φ is a dot product of magnetic flux density and area. The unit of the flux is Weber (WB).
