11. Armature reaction is demagnetizing in nature due to purely lagging load.
A. True
B. False
Answer: A
Due to purely lagging load, armature current is in the opposite phase with the field magneto-motive force. Armature magneto-motive force produced due to this current will be in the opposite phase with the field flux. It will try to reduce the net magnetic field.
12. The unit of Magento-motive force is Ampere-turns.
A. True
B. False
Answer: A
The magneto-motive force is defined as the product of current and turns. It is mathematically expressed as F=NI.
13. Calculate the velocity of the wheel if the angular speed is 25 rad/s and the radius is 10 m.
A. 250 m/s
B. 260 m/s
C. 270 m/s
D. 240 m/s
Answer: A
The velocity of the wheel can be calculated using the relation
V=ω×r.
The velocity is the vector product of angular speed and radius.
V=Ω×r = 25×10 = 250 m/s.
14. Displacement is a ____________ quantity.
A. Scalar
B. Vector
C. Scalar and Vector
D. Tensor
Answer: B
Displacement is a vector quantity. It depends on the initial and final position of the body. It has both direction and magnitude. Distance is a scalar quantity.
15. When a UJT is used for triggering an SCR, then the wave shape of voltage obtained from the UJT circuit will be ____________
A. Square
B. Pulse
C. Trapezoidal
D. Saw-tooth
Answer: B
UJT relaxation oscillator using RC circuit is used for SCR triggering and the wave shape obtained is an exponentially decaying pulse. So, we can say pulse waveform is obtained.
16. Calculate the value of the frequency if the period of the signal is 0 sec.
A. infinity
B. 0.4 Hz
C. 0.2 Hz
D. 0.78 Hz
Answer: A
The frequency is defined as the number of oscillations per second. It is reciprocal to the time period. It is expressed in Hz.
F = 1÷0 = infinity.
It signifies the signal is aperiodic.
17. The slope of the I-V curve is 87°. Calculate the value of resistance. Assume the relationship between voltage and current is a straight line.
A. 0.0524 Ω
B. 0.0254 Ω
C. 0.0543 Ω
D. 0.0648 Ω
Answer: A
The slope of the I-V curve is reciprocal to resistance. The slope given is 87° so
R=1÷tan(87°)=.0524 Ω.
18. The most suitable device for high-frequency inversion in switching mode power supply is ______
A. GTO
B. BJT
C. MOSFET
D. IGBT
Answer: C
MOSFET is the fastest among all the power semiconductor devices and has the highest frequency range. MOSFET stands for metal oxide silicon field-effect transistor.
19. In DC chopper, the waveform for input and output voltages is respectively __________
A. Discontinuous and Continuous
B. Continuous and Discontinuous
C. Both continuous
D. Both discontinuous
Answer: B
Chopper has a perfect DC at the input which is chopped into pulses which means the output voltage is discontinuous and by varying the duty cycle we can vary the average output voltage.
20. A chopper behaves as a __________
A. DC equivalent of AC switching device
B. DC equivalent of AC transformer
C. DC equivalent of AC relay
D. AC equivalent of circuit breaker
Answer: B
A chopper is used to step up or step down the DC voltage whereas the transformer is used to step up or step down AC voltage so the chopper is the DC equivalent of the AC transformer.
