21. Permanent magnet DC motor is more expensive than an Induction motor.
A. True
B. False
Answer: A
A permanent magnet DC motor is more expensive than an Induction motor because of the magnetic used in it. Magnets are made up of ferromagnetic material which results in high cost.
22. Calculate the line voltage in star connection when phase voltage=311 V.
A. 548.29 V
B. 538.66 V
C. 587.28 V
D. 185.58 V
Answer: B
The line voltage in the case of star connection is 1.73 times of phase voltage. It leads the phase voltage by an angle of 30°.
VL-L = 1.73×311 = 538.66 V.
23. The slope of the V-I curve of a solar cell is 66.1°. Calculate the value of resistance. Assume the relationship between voltage and current is a straight line.
A. 3.5 Ω
B. 2.2 Ω
C. 2.5 Ω
D. 2.9 Ω
Answer: B
The slope of the V-I curve of a solar cell is resistance. The slope given is 66.1° so
R=tan(66.1°)=2.2 Ω.
The slope of the I-V curve is reciprocal to resistance.
24. SCIM has a _________
A. Shorter life
B. Medium life
C. Longer life
D. Infinite life
Answer: C
SCIM stands for squirrel cage induction motor. It has high efficiency, maintenance-free operation, and long life because of its rigid nature.
25. The power factor of a SCIM generally is ___________
A. .1-.2
B. .6-.8
C. .3-.4
D. .5-.7
Answer: B
At light loads, the current drawn is largely a magnetizing current due to the air gap and hence the power factor is low. The power factor of a SCIM generally is .6-.8.
26. Calculate the active power in a 11710 H inductor.
A. 8245 W
B. 1781 W
C. 0 W
D. 1964 W
Answer: C
The inductor is a linear element. It only absorbs reactive power and stores it in the form of oscillating energy. The voltage and current are 90° in phase in the case of the inductor so the angle between V & I is 90°.
P = VIcos90° = 0 W.
27. Calculate the frequency of the waveform i(t) = sin(πt+π÷4)+sin(πt+π÷74).
A. .5 Hz
B. .8 Hz
C. .1 Hz
D. .9 Hz
Answer: A
The fundamental time period of the sine wave is 2π.
The time period of i(t) is L.C.M {2,2}=2 sec.
The frequency of the waveform is 1/2 = .5 Hz. The time period is independent of phase shifting and time-shifting.
28. Full form of CEL is ____________
A. Central Electronics Limited
B. Central Electrical Limited
C. Circle Electronics Limited
D. Circle Electrical Limited
Answer: A
The full form of CEL is Central Electronics Limited. It is a Government of India enterprise founded in 1974. It is a publicly listed company.
29. Full form of BEL is ____________
A. Busy Electronics Limited
B. Burden Electrical Limited
C. Bharat Electronics Limited
D. Brahma Electrical Limited
Answer: C
The full form of BEL is Bharat Electronics Limited. It is a Government of India enterprise founded in 1954. It is a publicly listed company.
30. Material used for making solar cell is _________
A. Silicon
B. Carbon
C. Sodium
D. Magnesium
Answer: A
The material used for making solar cells is Silicon. It is a naturally obtained semi-conductor. It has a lower cut-off voltage and minimum energy bandgap.
