501 MCQ Questions on DC Machine

351. Which is the correct statement?

(a) In a dc commutator motor, the rotor has permanent magnet.
(b) In a brush less dc motor, the rotor has permanent magnet.
(c) In a hybrid stepper motor, the stator has a permanent magnet.
(d) Multi stack variable reluctance motor has permanent magnet on rotor. [FCI – 2015]

352. In an electromechanical energy conversion device, the developed torque depends upon

(a) stator field strength and torque angle.
(b) stator field strength and rotor field strength.
(c) stator field and rotor field strengths and torque angle
(d) stator field strength only. [FCI – 2015]

353. A d.c. series motor is accidently connected to single phase a.c. supply. The torque produced will be

(a) of zero average value.
(b) oscillating.
(c) steady and unidirectional.
(d) pulsating and unidirectional. [FCI – 2015]

354. In a separately excited dc motor controlled by a single phase semi-converter drive, under continuous armature current condition, no load speed is proportional to

(a) 1 + cos α
(b) cos α
(c) sin α
(d) 1 + sin α

355. In case of DC series motor, it is possible to have finite no-load speed if a resistance is connected across its

(a) field terminals.
(b) armature terminals.
(c) field and armature together.
(d) It is not possible. [Uttarakhand AE 2013]

356. Two identical loss less series motors are connected in series across a DC supply voltage run at speeds of N₁, and N₂. The ratio of their output will be

(a) N₂² : N₁²
(b) N₁ : N₂
(c) N₂ : N₁
(d) 1 : 1 [Uttarakhand AE – 2013]

357. Field control of a DC shunt motor gives

(a) constant kW drive.
(b) constant torque drive.
(c) constant speed drive.
(d) variable load speed drive. [Uttarakhand AE – 2013]

358. Which of the following motors is preferred when quick speed reversal is the main consideration? [Uttarakhand AE – 2013]

(a) Squirrel cage induction motor.
(b) Wound rotor induction motor.
(c) Synchronous motor.
(d) D.C. motor.

359. In a DC machine, the angle between the stator and rotor fields is

(a) dependent upon the load.
(b) 45°
(c) 90°
(d) 180° [Uttarakhand AE – 2013]

360. At the time of starting the motor current …….. than normal.

(a) same
(b) high
(c) low
(d) none of these

361. In a DC motor, unidirectional torque is produce with the help of

(a) brushes
(b) commutator
(c) end plates
(d) both a and b

362. The current drawn by a 120 V DC motor of armature resistance 0.5 Ω and back emf 110 V is ……….. (ampere).

(a) 20
(b) 240
(c) 220
 (d) 5

363. When the direction of power flow reverses, a differentially compounded DC motor becomes

(a) a shunt motor.
(b) a series motor.
(c) a cumulatively compounded generator.
(d) a differentially compounded generator. [BSNL TTA – 2016]

364. In a DC motor which of the following can sustain the maximum temperature rise?

(a) armature winding.
(b) field winding.
(c) commutator.
(d) slip-ring.

365. If the flux of a dc motor approached zero

(a) its speed will approach zero.
(b) the motor will tend to run at infinite speed.
(c) the motor will stop.
(d) its speed will remain unchanged. [BSNL TTA – 2016]

366. The speed of a DC series motor decreases if the flux in the field winding

(a) remains constant.
(b) increases.
(c) decreases.
(d) None of these. [BSNL TTA – 2015]

367. A DC shunt motor is running at light load. What will happen if the field winding gets opened. [BSNL TTA 2016]

(a) Motor will pick up high speed.
(b) Motor will stop.
(c) Motor will make noise.
(d) Motor will burn.

368. In AC series motor, armature coils are usually connected to commutator through

(a) resistance.
(b) inductors.
(c) capacitors.
(d) solid contact. [UPRVUNL – 2015]

369. Which of the following motors is used for centrifugal pumps?

(a) Series Motor
(b) Shunt motor
(c) Induction motor
(d) Either series or shunt [UPRVUNL – 2015]

370. A DC motor is preferred over an AC motor due to

(a) high speed operation.
(b) low speed operation.
(c) fixed speed operation.
(d) variable speed operation. [UPRVUNL – 2015]

371. Motor used for punching machine is subjected to

(a) no load.
(b) continuous part load.
(c) continuous full load
(d) intermittent load.

372. A face plate starter is used to start

(a) induction motor.
(b) universal motor.
(c) synchronous motor.
(d) dc series motor. [UPRVUNL – 2015]

373. Plugging provides

(a) zero torque braking.
(b) highest torque braking.
(c) indeterminate torque braking.
(d) smallest torque braking. [UPRVUNL 2015]

374. The speed regulation of a motor falls from 1100 rpm at no load to 1050 rpm at rated load. The speed regulation of the motor is

(a) 2.36%
(b) 4.76%
(c) 6.77%
(d) 8.84% [UPRVUNL – 2015]

375. Consider the following statements regarding a DC motor. When the speed of a DC motor increases

1. Back emf decreases
2. Current drawn increases

(a) Only 2
(b) Only 1
(c) Both 1 and 2
(d) Neither 1 nor 2 [UPRVUNL – 2015]

376. The ratio of starting torque to full load torque is least in the case of

(a) series motor.
(b) shunt motor.
(c) differentially compounded.
(d) cumulative compounded. [UPRVUNL – 2015]

377. Speed of a DC motor is

(a) inversely proportional to the air-gap flux.
(b) directly proportional to the air-gap flux.
(c) inversely proportional to the square of air-gap flux.
(d) not related to the air-gap flux. [UPRVUNL – 2014]

378. The function of a starter in a d.c. motor is to

(a) reduce voltage.
(b) insert resistance in field circuit.
(c) insert resistance in armature circuit.
(d) control the speed. [DMRC – 2015]

379. A DC shunt motor is running at 1200 rpm, when excited with 220V DC. Neglecting the losses and saturation, the speed of the motor when connected to a 175 V supply is

(a) 70 rpm
(b) 900 rpm
(c) 1050 rpm
(d) None of these [DMRC – 2014]

280. As the motion of armature increases, back e.m.f.

(a) increases.
(b) decreases.
(c) remains constant.

381. In DC machines, fractional pitch winding is used to

(a) improve cooling.
(b) reduce copper losses.
(c) increase the generated emf.
(d) reduce the sparking. [LMRC 2015]

382. The speed of DC motor is proportional to the

(a) armature current.
(b) square of armature current.
(c) field current.
(d) inverse of armature current. [LMRC – 2015]

383. A 4 pole DC machine is running at 1500 rpm. What is the frequency of current in armature winding? [LMRC – 2015]

(a) 25 Hz
(b) 0 Hz
(c) 100 Hz
(d) 50 Hz

384. A differentially compound D.C. motor runs at a full load speed of 1000 rpm. If its series field winding is short circuited, then its full-load speed

(a) becomes more than 1000 rpm.
(b) becomes less than 1000 rpm
(c) remains 1000 rpm.
(d) motor first accelerates and then stops with jerks.

385. In a dc shunt motor, at 4 amp. the torque developed is 20 Nm. If the load current doubles, what is obtained value of torque? [JMRC – 2012]

(a) 10 Nm
(b) 20 Nm
(c) 40 Nm
(d) 80 Nm

356. Two DC series motors connected in series draw current I from supply and run at speed N. When the same motors are connected in parallel to the same supply, what will be the speed of both motors? [JMRC – 2012]

(a) N
(c) 4N
(b) 2N
(d) N/2

387. What does the nominal power printed on the name plate of any motor signify? [JMRC – 2012]

(a) Power drawn in KVA
(b) Output power at the shaft
(c) Power drawn in kW
(d) The gross power

388. Laminations of core are generally made of

(a) cast iron.
(b) carbon.
(c) silicon steel.
(d) stainless steel. [DSSB – 2015]

389. Which of the following could be approximately the thickness of laminations of a DC machine? [DSSB – 2015]

(a) 0.005 mm
(b) 0.05 mm
(c) 0.5 mm
(d) 5 m

390. Copper brushes in DC machine are used

(a) where low voltage and high currents are involved.
(b) where high voltage and small currents are involved.
(c) in both of the above cases.
(d) in none of the above cases. [DSSB – 2015]

391. Iron losses in a D.C. machine are independent of variations in

(a) speed.
(b) load.
(c) voltage.
(d) speed and voltage. [DSSB – 2015]

392. In case of D.C. machine winding, number of commutator segments are equal to

(a) number of armature coils.
(b) number of armature coil sides.
(c) number of armature conductors.
(d) number of armature turns. [DSSB – 2015]

393. For a DC machines laboratory following type of D.C. supply will be

(a) rotary converter.
(b) mercury arc rectifier.
(c) induction motor d.c. generator set.
(d) synchronous motor d.c. generator set [DSSB – 2015]

394. Which of the following application requires high starting torque? [DSSB – 2015]

(a) Lathe machine
(b) Centrifugal pump
(c) Locomotive
(d) Air blower

395. If a D.C. motor is to be selected for conveyors, which motor would be preferred? [DSSB – 2015]

(a) Series motor
(b) Shunt motor
(c) Differential compound motor
(d) Cumulative compound motor

396. Differential compound D.C. motors can find applications requiring

(a) high starting torque.
(b) low starting torque.
(c) variable speed.
(d) frequent on-off cycles. [DSSB – 2015]

397. The armature torque of the D.C. shunt motor is proportional to

(a) field flux only.
(b) armature current only.
(c) both (a) and (b).
(d) none of the above. [DSSB – 2015]

398. Which of the following methods of speed control of D.C. machines will offer minimum efficiency?  [DSSB – 2015]

(a) Voltage control method
(b) Field control method
(c) Armature control method
(d) All of the above methods

399. For a D.C. shunt motor if the excitation is changed

(a) torque will remain constant.
(b) torque will change but power will remain constant.
(c) torque and power both will change.
(d) torque, power and speed, all will change.

400. If the speed of a D.C. shunt motor is increased, the back e.m.f. of the motor will

(a) increase.
(b) decrease.
(c) remain same.
(d) become zero. [DSSB – 2015]