# Objective questions and answers or MCQ of Electrical Machines page-15

236. The utilization factor is maximum for

a) Three-phase mercury arc rectifier
b) Six-phase mercury arc rectifier
c) twelve-phase mercury arc rectifier
d) Single phase mercury arc rectifier

Ans: (a)

237. If the air gap of the induction motor is increased

a) The power factor will increase
b) The power factor will decrease
c) The magnetizing current of the rotor will increase
d) The magnetizing current of the rotor will decrease
e) The speed of the motor will decrease

Ans: (d)

238. The squirrel cage induction motor has

a) One slip rings
b) two slip rings
c) three slip rings
d) zero slip rings

Ans: (d)

239. What will happen if the supply terminals of d.c. shunt motor are interchanged

a) motor will stop
b) motor will run at its normal speed in the same direction as it was running
c) the direction of rotation will reverse
d) motor speed will increase

Ans: (c)

240. An amplidyne can be used as

a) a d.c. series motor
b) a d.c. shunt motor
c) a d.c. compound motor
d) magnetic amplifier

Ans: (c)

241. The torque/slip characteristic of induction motor is shown, which is the unstable region?

a) A
b) B
c) C
d) D

Ans: (b)

242. Find the odd man out

a) Tachometer
b) Voltmeter
c) Ammeter
d) Galvanometer

Ans: (a)

243. The mechanical load across the induction motor is equivalent to electrical load of

a) R2 (1/s – 1)
b) R2 (1/s – 1)
c) R2 (s – 1)
d) 1/R2 (s – 1)

Ans: (b)

Where R2 is the resistance of the rotor in terms of secondary and s is the slip of motor.

244. If the supply frequency to the transformer is increased the iron loss

a) Will decrease
b) Will increase
c) Will not change
d) Will reach nearly zero

Ans: (b)

245. In the d.c. motors iron losses occur in

a) The yoke
b) The pole shoe
c) The armature
d) The field

Ans: (b)

246. With the use high flux density in the transformer

a) The size of core will decrease
b) Less copper will be used
c) Core losses will decrease
d) Voltage output will decrease

Ans: (a)

247. The induced e.m.f. in the armature of d.c. machine rotating in the stationary field will be

a) Sinusoidal voltage
b) Direct voltage
c) Sinusoidal with even harmonics
d) Sinusoidal with oil harmonics

Ans: (a)

248. The air gap between poles has

a) No magnetic field
b) No magnetic unless the poles are far apart
c) A strong magnetic field
d) A magnetic field if the poles tough

Ans: (c)

249. Magnetic induction results in

a) Induced poles opposite from the original poles
b) Induced poles the same as the original field
c) Two north poles
d) An induced magnetic field but no induced pole

Ans: (a)

250. Which of the following statement is true?

a) Iron, steel, and nickel are magnetic materials.
b) Copper, iron, steel, and air are magnetic materials.
c) Paper, wood, and steel are magnetic materials.
d) Iron is magnetic materials but steel is non-magnetic.

Ans: (a)