MCQ in AC Motors Part 5 | REE Board Exam

This is the Multiple Choice Questions Part 5 of the Series in AC Motors as one of the Electrical Engineering topic. In Preparation for the REE Board Exam make sure to expose yourself and familiarize in each and every questions compiled here taken from various sources including but not limited to past Board Exam Questions in Electrical Engineering field, Electrical Engineering Books, Journals and other Electrical Engineering References.

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⇐ MCQ in AC Motors Part 4 | REE Board Exam

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201.  A 3Φ, induction motor is wound for 4 poles and is supplied from a 50 Hz system. What is the rotor frequency when rotor runs at 1410 rpm?

A.  3 Hz

B.  2.5 Hz

C.  2.9 Hz

D.  3.5 Hz

SINGLE PHASE MOTORS

202.  Most of single-phase induction motors are ____ machines.

A.  2 pole

B.  6 pole

C.  8 pole

D.  4 pole

203.  The main winding and starting winding of a single -phase induction motor are connected in ____ across the supply.

A.  series

B.  parallel

C.  series-parallel

D.  none of these

204.  The starting winding of a single-phase induction motor has ____ that of the main winding.

A.  more poles than

B.  less poles than

C.  same number of poles

D.  none of these

205.  A 50 Hz, 4 pole single-phase induction motor will have a synchronous speed of

A.  1500 rpm

B.  750 rpm

C.  1200 rpm

D.  none of these

206.  A 4 pole, 50 Hz single-phase induction motor has a slip of 5%. The speed of the motor will be

A.  1500 rpm

B.  1425 rpm

C.  1200 rpm

D.  none of these

207.  In a single-phase induction motor, speed sensitive centrifugal switch is connected in ____ winding.

A.  parallel with main

B.  series with main

C.  series with starting

D.  parallel with starting

208.  The purpose of starting winding in a singlephase induction motor is to

A.  reduce losses

B.  limit temperature rise of the machine

C.  produce rotating flux in conjunction with main winding

D.  none of these

209.  If I_m and I_s are the current in the main and starting windings respectively and α is the angle between Im and Is, then motor torque T is given by

A.  T α I_m I_s cos α

B.  T α I_m I_s sin α

C.  T α I_m I_s

D.  none of these

210.  In the resistance split-phase induction motor shown in Fig. 1, the angle α between I_m and I_s is about

A.  80 degrees

B.  65 degrees

C.  75 degrees

D.  25 degrees

211.  The starting winding of a split-phase induction motor shown in Fig. 1 is disconnected when the motor attains about ____ of synchronous speed.

A.  75%

B.  50%

C.  25%

D.  100%

212.  In the resistance split-phase induction motor shown in Fig. 1, the main windings has

A.  high resistance and high inductance

B.  high resistance and low inductance

C.  low resistance and high inductance

D.  low resistance and low inductance

213.  At starting, the current Is in the starting winding shown in Fig. 1

A.  lags V by 90 degrees

B.  leads V by 90 degrees

C.  is nearly in phase with V

D.  leads V by 75 degrees

214.  A resistance split-phase induction motor is used for

A.  low inertia loads

B.  high inertia loads

C.  very high inertia loads

D.  none of these

215.  The direction of split-phase induction motor can be reversed by interchanging the connections of supply of

A.  either main or starting winding

B.  both main and starting winding

C.  rotor winding

D.  none of these

216.  The resistance split-phase induction motor has ____ starting torque.

A.  high

B.  moderate

C.  very low

D.  none of these

217.  The resistance split-phase induction motor is used in those applications where

A.  starting is frequent

B.  starting period is long

C.  starting is infrequent

D.  none of these

218.  The resistance split-phase induction motors are the most popular single-phase induction motors because of

A.  their low cost

B.  their high starting torque

C.  the long starting period

D.  none of these

219.  In the capacitor start induction motor shown in Fig. 2, the angle α between I_m and I_s is

A.  exactly 90°

B.  about 30°

C.  about 40°

D.  about 75°

220.  The value of Is in capacitor-start motor shown in Fig. 2 is ____ the current I_m.

A.  equal to

B.  less than that of

C.  more than that of

D.  none of these

221.  The capacitor C used in the capacitor-start motor shown in Fig. 2 is always a ____ capacitor.

A.  paper

B.  ceramic

C.  mica

D.  electrolytic

222.  At starting, the line current of a capacitor-start induction motor is ____ normal full-load current.

A.  8 to 10 times

B.  4 to 5 times

C.  equal to

D.  7 to 8 times

223.  In a capacitor-start, capacitor-run motor, ____ winding is cut-out after starting.

A.  starting

B.  main

C.  neither A or B

D.  none of these

224.  A capacitor-start, capacitor-run motor has

A.  low power factor

B.  high power factor

C.  low efficiency

D.  high starting torque

225.  The capacitor-start, capacitor-run induction motor acts as a true 2-phase motor at

A.  starting

B.  no load

C.  all loads

D.  full load

226.  The capacitor-start, capacitor-run motor is used in those applications where

A.  highly starting torque is required

B.  silence is important

C.  noisy operation is not important

D.  none of these

227.  The capacitor-start, capacitor-run motor has

A.  no centrifugal switch

B.  low power factor

C.  noisy operation

D.  low efficiency

228.  Capacitor motors ____ resistance split-phase induction motors.

A.  are costlier than

B.  are less costly than

C.  cost about the same as

D.  poor starting torque than

229.  Most of the troubles of single-phase induction motor are traceable to the

A.  rotor bars

B.  main winding

C.  shaft bearings

D.  starting switch

230.  The single-phase shaded pole motor has

A.  squirrel cage rotor

B.  wound rotor

C.  high power factor

D.  high starting torque

231.  The direction of rotation of shaded pole motor depends upon

A.  supply frequency

B.  number of poles on the stator

C.  which half of the pole is shaded

D.  supply voltage

232.  The full-load efficiency of a shaded pole motor is about

A.  70 to 80%

B.  60 to 70%

C.  30 to 35%

D.  5 to 10%

233.  The single-phase series motor can operate on

A.  ac only

B.  dc only

C.  both ac and dc

D.  none of these

234.  For the same rating, a dc series motor costs _____ single phase series motor.

A.  about the same as

B.  more than

C.  less than

D.  none of these

235.  A 2 HP dc series motor will weigh ___ 2 HP single-phase series motor.

A.  about the same as

B.  less than

C.  more than

D.  none of these

236.  A vacuum cleaner employs ____ motor.

A.  resistance split-phase

B.  capacitor start

C.  shaded-pole

D.  single-phase series

237.  The best suited motor to drive a 1/4 HP fan in a hospital would be ____ motor.

A.  shaded pole

B.  single-phase series

C.  capacitor run

D.  hysteresis

238.  The washing machine generally employs ____ motor.

A.  single-phase series motor

B.  resistance split-phase

C.  shaded-pole

D.  hysteresis

239.  The best suited motor to drive a 3/4 HP air compressor would be ____ motor.

A.  capacitor start

B.  single-phase series

C.  shaded pole

D.  resistance split-phase

240.  The least expensive fractional horsepower motor is

A.  shaded pole

B.  capacitor-start

C.  split phase

D.  ac series

241.  The starting winding of a single-phase motor is placed in the

A.  rotor

B.  stator

C.  armature

D.  field

242.  One of the characteristics of a single-phase motor is that it

A.  is self-starting

B.  is not self-starting

C.  requires only one winding

D.  can rotate in one direction only

243.  After the starting winding of a single phase induction motor is disconnected from supply, it continues to run only on ____ winding.

A.  rotor

B.  field

C.  compensating

D.  running

244.  If starting winding of a single-phase induction motor is left in the circuit, it will

A.  draw excessive current and overheat

B.  run slower

C.  run faster

D.  spark at light loads

245.  The direction of rotation of a single-phase motor can be reversed by

A.  reversing connections of both windings

B.  reversing connections of starting winding

C.  using a reversing switch

D.  reversing supply connections

246.  If a single-phase induction motor runs slower than normal, the more likely defect is

A.  improper fuses

B.  shorted running winding

C.  open starting winding

D.  worn bearing

247.  The capacitor in a capacitor-start induction run ac motor is connected in series with ____ winding.

A.  starting

B.  squirrel-cage

C.  running

D.  compensating

248.  A permanent-split single-phase capacitor motor does not have

A.  centrifugal switch

B.  starting winding

C.  squirrel-cage rotor

D.  high power factor

249.  The starting torque of a capacitor-start induction-run motor is directly related to the angle or between its two winding currents by the relation

A.  cos

B.  sin

C.  tan

D.  sin /2

250.  In a two-value capacitor motor, the capacitor used for running purposes is a/an

A.  dry-type ac electrolytic capacitor

B.  paper-spaced oil filled type

C.  air-capacitor

D.  ceramic type

Questions and Answers in AC Motors

Following is the list of practice exam test questions in this brand new series: