26. Dielectric heating is also called
(a) Volume heating
(b) infrared heating
(c) surface heating
(d) eddy current heating
Answer: (a) Volume heating
27. Voltage drop is the main consideration while designing a
(a) Feeder
(b) Distributor
(c) Service main
(d) All the above
Answer: (b) Distributor
28. Laboratory wattmeters are
(a) Induction type
(b) Moving iron type
(c) Electrostatic type
(d) Electro-dynamometer type
Answer: (d) Electro-dynamometer type
29. An electric motor may give noise due to
(a) magnetic effect
(b) defective bearing
(c) cooling air
(d) all the above
Answer: (d) all the above
30. Which of the following motor is used in household refrigeration?
(a) Synchronous motor
(b) D.C. shunt motor
(c) 3-phase induction motor
(d) 1-phase induction motor
Answer: (d) 1-phase induction motor
31. The lighting arrester is connected
(a) in series with the line
(b) between line and earth
(c) to a pole near the line
(d) to circuit breaker
Answer: (b) between line and earth
32. If Rg in the circuit shown in figure is variable between 20 ohm and 80 ohm then maximum power transferred to the load RL will be
(a) 15 ohm
(b) 13.33 ohm
(c) 6.67 ohm
(d) 2.4 ohm
Answer: (a) 15 ohm
33. The knowledge of diversity factor helps in computing
(a) plant capacity
(b) average load
(c) units generator
(d) peak density
Answer: (d) peak density
34. Distribution transformers are designed to have maximum efficiency nearly at
(a) 100% of full load
(b) 50% of full load
(c) 25% of full load
(d) 10% of full load
Answer: (b) 50% of full load
35. Electronic switching are becoming more and more popular because of
(a) noiseless operation
(b) long life
(c) smaller size and weight
(d) all the above
Answer: (d) all the above
36. The controlling torque in gravity controlled meter is proportional to
(a) cos θ
(b) sin θ
(c) tan θ
(d) θ
Answer: (b)
For gravity control TC α sin θ
For spring control TC α θ
37. The condition for a maximum power output from dc motor is
(a) Eb = V
(b) Eb = V/2
(c) Eb = 0
(d) Eb = V/√2
Answer: (b) Eb = V/2
38. Time constant of th network shown in figure is
(a) 2 RC
(b) 3 RC
(c) RC/2
(d) 2RC/3
Answer: (d) 2RC/3
39. A 2 kVA transformer has iron loss of 150 W and full load copper loss of 250 W. The maximum efficiency of the transformer will occur when the total loss is
(a) 500 W
(b) 400 W
(c) 300 W
(d) 275 W
Answer: (c) 300 W
40. While starting synchronous motor its field winding should be
(a) kept open
(b) connected to a dc source
(c) connected to ac source
(d) kept short-circuited
Answer: (d) kept short-circuited
41. A 4-pole, 3-phase induction motor is running at 4% slip at full load. If the speed of the motor is 750 rpm, the supply frequency is
(a) 16 x 2/3 Hz
(b) 25 Hz
(c) 50 Hz
(d) 60 Hz
Answer: (b) 25 Hz
42. An oscillator uses
(a) Positive feedback
(b) Negative feedback
(c) Both positive and negative feedback
(d) No feedback
Answer: (a) Positive feedback
43. Permeans is analogous to
(a) Conductance
(b) Reluctance
(c) Inductance
(d) Resistance
Answer: (a) Conductance
44. A wire has a resistance 10 ohms. It is stretched by one-tenth of its original length. Then its resistance will be
(a) 10 ohms
(b) 12.1 ohms
(c) 9 ohms
(d) 11 ohms
Answer: (b) 12.1 ohm
45. Potential transformer are used
(a) to measure high a.c. voltage
(b) to measure high d.c. voltage
(c) both (a) and (b)
(d) as protective device in high voltage circuits
Answer: (a) to measure high a.c. voltage
46. To increase the range of a voltmeter
(a) a low resistance is connected in series
(b) a low resistance is connected in parallel
(c) a high resistance is connected in series
(d) a high resistance is connected in parallel
Answer: (c) a high resistance is connected in series
47. A three phase power transformer is provided with star-delta connections. In order to protect angainst fault, connection for current transformer should be in
(a) Star-star
(b) Delta-star
(c) Delta-delta
(d) Star-delta
Answer: (b) Delta-star
48. For active region operation of NPN transistor
(a) Emitter is positive with respect to base
(b) Emitter is –ve with respect to base
(c) Emitter is at same voltage as base
(d) base is at same voltage as collector
Answer: (b) Emitter is –ve with respect to base
49. The advatage of electric breaking is
(a) It is instantaneous
(b) More heat is generated during breaking
(c) it avoids wear of track
(d) Motor continue to remain load druing breaking
Answer: (d) Motor continue to remain load druing breaking
50. A single phase motor is made-starting by the addition of a / an
(a) Running winding
(b) Starting winding
(c) Electric starter
(d) Autotransformer
Answer: (b) Starting winding