501 MCQ Questions on DC Machine

301. D.C. generators works on the principle of

(a) Electromagnetic Induction
(b) Ohm’s Law
(c) Lenz’s Law
(d) Kirchoff’s Law [RRB JE 2015]

302. Frequency of a generator when the number of poles are 8 and speed is 750 rpm will be

(a) 50 Hz
(b) 52 Hz
(c) 60 Hz
(d) 65 Hz [UPPCL JE – 2016]

303. In electrical machines, magnetic leakage is undesirable. This is due to the fact that it

1. Lowers the power efficiency
2. Produces fringing
3. Leads to their increased weight

The correct amongst them is/are
(a) Only 1
(b) 1, 2 and 3
(c) Only 2
(d) Both 2 and 3 [UPPCL – 2016]

304. When a dynamo convertes electrical energy into mechanical energy, it is called

(a) motor
(b) generator
(c) producer
(d) inverter [RRB-JE – 2015]

305. When a DC series motor is connected to AC supply, the power factor will be low because of

(a) high inductance of field and armature circuits.
(b) induced current in rotor due to variation of flux.
(c) fine copper wiring winding.
(d) low inductance of field and armature circuits.

306. For punch and crane applications the ……….  are used. [UPRVUNL JE – 2016]

(a) starting, stopping, speed controllers and reversing
(b) speed controllers
(c) starting, stopping
(d) reversing

307. The mechanical power developed by a motor is maximum when

(a) back emf is zero.
(b) back emf is equal to half the applied voltage.
(c) back emf is less than the applied voltage.
(d) back emf is greater than the applied voltage [UPRVUNL JE 2016]

308. If we connect two DC series motor in parallel, then in comparison to the normal speed, the resultant speed will be

(a) less.
(b) equal.
(c) more.
 (d) zero.

309. ……..braking is generally used in braking of battery operated scooters.

(a) Plugging
(b) Regerative
(c) Mechanical
(d) Rheostatic [UPPCL JE – 2016]

310. For a DC Motor for constant load torque, what will happen to the armature current if armature resistance increases? [UP JAL NIGAM AE-2016]

(a) Remain unchanged
(b) Increases
(c) Decreases
(d) None of the above

311. If the variable losses in a DC motor is 600 W. Then for maximum efficiency of the motor, the constant losses must be

(a) 300 W
(b) 1200 W
(c) 600 W
(d) 100 W

312. Which type of frame is preferred for motors in moisture surrondings? [JUVNL JE – 2017]

(a) Splash proof
(b) Drip proof
(c) Open type
(d) Totally enclosed fan cooled

313. What is the maximum power rating of DC motor to start with a direct on-line starter?

(a) 5 HP
(b) 1 HP
(c) 20 HP
(d) 10 HP

314. Which type of DC motor is confined for a brake test?

(a) Small horse power motors
(b) High speed motors
(c) High horse power motors
(d) Variable speed motors

315. Which element(s) is/are used in the starter for a DC shunt motor?

(a) Inductor
(b) Capacitor
(c) Combination of resistor and capacitor
(d) Resistor

316. The method of speed control of DC shunt motors used for application where a very wide range sensitive speed control is required is

(a) Ward-Leonard system.
(b) multiple voltage control.
(c) tapped field control.
(d) rheostatic control. [NMRC – 2017]

317. The three-point starter can be used for

(a) both shunt and compound motors
(b) shunt motor only
(c) series motor only
(d) compound motor only [NMRC – 2017]

318. There will be ……….. in the speed of DC shunt motor with the increasing load. [UPPCL – 2016]

 (a) slight reduction
(c) no change
(b) proportional change
(d) slight enhancement

319. Which motor is used where high starting torque and wide speed range control is required? [LMRC JE – 2016]

(a) Single phase capacitor start motor
(b) DC motor
(c) Induction motor
(d) Synchronous motor

320. For a DC series motor, if T_a be the torque and I_a the armature current, then which relation is valid for the condition before saturation?

(a) T_a α I_a
(b) T_a α I_a²
(с) T_a α 1/I_a
(d) T_a α 1/I_a²

321. Which of the following is not necessarily the advantage of D.C. motor over A.C. motor?

(a) High starting torque
(b) Wide speed range
(c) Better speed control
(d) Low cost [UJVNL-2016]

322. The armature current of a D.C. motor is given by

 (a) I_a = (V + E_b)/R_a
(b) I_a = (V – E_b)/R_a
(c) I_a = (V – R_a)/E_b
(d) I_a = (R_a – E_b)/V

323. A D.C. motor can easily be Identified by

(a) yoke.
(b) size of conductor.
(c) commutator.
(d) windings.

324. A 150 kW electric motor has an efficiency of 90%, when it operates at full load. Calculate the losses in the machine. [Jammu & Kashmir JE – 2016]

(a) 92 kW
(b) 150 kW
(c) 163 kW
(d) 16.66 kW

325. If the load current and flux of a DC motor are held constant, and voltage applied across its armature is increased by 10%, its speed will

(a) decreased by 10%.
(b) remain unchanged.
(c) increase by 10%.
(d) increase by 20%. [J&K JE – 2016]

326. A shunt motor rotating at 1500 r/min is fed by a 120 V source. The line current is 51 A and the shunt field resistance is 120 ohm. If the armature resistance is 0.1 ohm, calculate the current in the armature. [J & K JE – 2016]

(a) 1 A
(b) 51 A
(c) 50 A
(d) 12 A

327. The d.c. series motor should always be started with load because

(a) it will fail to start.
(b) it will not develop high starting torque.
(c) at no load, it will rotate at dangerously high speed.
(d) all are true. [Uttarakhand AE 2013]

328. Which of the following testing methods is a direct testing of DC machine? [J&K JE – 2016]

(a) Swinburne’s test
(b) Field test
(c) Hopkinson’s test
(d) Brake test

329. Ward-leonard controlled DC drives are generally used for

(a) light duty excavators.
(b) medium duty excavators.
(c) heavy duty excavators.
(d) low duty excavators. [J&K JE – 2016]

330. What is the order of the characteristic equation of an armature controlled DC motor? [J & K JE – 2016]

(a) First order equation
(b) Second order equation
(c) Zero order equation
(d) Third order equation

331. The armature windings in a dc motor are placed on

(a) stator only.
(b) rotor only.
(c) either stator or rotor.
(d) none of the other options. [UPRVUNAL AE-2014]

332. ………. is a property of differentially compounded DC motor.

(a) Low starting torque
(b) Variable speed
(c) High starting toque
(d) Infinite speed at no-load

333. For a d.c. series motor, which of the following expression is correct assuming torque (T) versus armature current (I) Characteristics unsaturated? [Uttarakhand – 2013]

(a) T α φ √I_a
(b) T α φI_a
(c) T α √(φI_a)
(d) T α φ²I_a²

334. In shunt motors, the method of speed control is/are

1. Variable resistance in field circuit
2. Variable resistance in armature circuit
3. Tapping the field
4. Field diverter

(a) 2 and 4
(b) 3 and 4
(c) 1 and 4
(d) 1 and 2 [UPPCL 2016]

335. In DC shunt motors, as load is reduced then the speed will be

(a) increase abruptly.
(b) increase in proportion to reduction in load.
(c) remain almost constant.
(d) reduce. [ESIC JE – 2016]

336. Which DC motor has got maximum self loading property? [ESIC JE 2016]

(a) Series motor
(b) Shunt motor
(c) Cumulatively compounded motor
(d) Differentially compounded motor

337. As compared to an induction motor, the air gap in a DC motor is

(a) less than 50%.
(b) between 50% to 90%.
(c) same.
(d) more. [ESIC JE 2016]

338. Field winding of a DC series motor is usually provided with thick wire

(a) to provide large flux.
(b) to reduce the use of insulating materials.
(c) as it carries large load current.
(d) in order to reduce eddy current. [ESIC JE – 2016]

339. For a DC shunt motor if the excitation is changed then

(a) torque will remain constant.
(b) torque will change but power will remain constant.
(c) torque and power both will change.
(d) all torque, speed and power will change. [ESIC JE – 2016]

340. Ward-Leonard control is basically a

(a) voltage control method.
(b) field diverter method.
(c) field control method.
(d) armature resistance control method. [ESIC JE – 2016]

341. DC shunt motors are used for driving

(a) trains.
(b) cranes.
(c) hoist.
(d) machine tools. [ESIC JE – 2016]

342. Which of the following tests will be suitable for testing two similar DC series motors of large capacity? [ESIC JE – 2016]

(a) Swinburne’s test
(b) Hopkinson’s test
(c) Field test
(d) Brake test

343. If a DC shunt motor is working at full load and if shunt field circuit suddenly opens

(a) this will make armature to take heavy current, possibly burning it.
(b) this will result in excessive speed, possibly destroying armature due to excessive centrifugal stress.
(c) nothing will happen to motor.
(d) motor will come to stop. [ESIC JE 2016]

344. A 230 V DC shunt motor takes 32 A at full load. The back e.m.f. on the full load, if the resistance of motor armature and shunt field winding are 0.2Ω and 115 Ω respectively, will be

(a) 210 V
(b) 215 V
(c) 220 V
(d) 224 V [ESIC JE 2016]

345. In a DC motor constant torque is produced due to

(a) rotor laminations.
(b) end-plates.
(c) pole shoes.
(d) commutator. [ESIC JE 2016]

346. The maximum end play of a motor is about

(a) 10 mm
(c) 2 mm
(b) 6 mm
(d) 0.4 mm [ESIC JE – 2016]

347. The mechanical power developed by a DC motor is equal to

(a) power input + losses.
(b) back e.m.f. x armature current.
(c) power output x losses.
 (d) power output x efficiency.

348. The variable resistor shunting the field of a DC series motor is called

(a) armature diverter.
(b) voltage regulator.
(c) field diverter.
(d) potential diverter. [ESIC JE – 2016]

349. Speed control by varying the armature circuit resistance, in a DC motor provides a

1. Constant torque drive
2. Constant power drive
3. Variable power drive

(a) Only 1
(b) Only 1 and 3
(c) Only 3
(d) Only 2 and 3 [ESIC JE – 2016]

350. Cranes generally offers

(a) reversing load and light start.
(b) gradually varying load.
(c) non reversing load and heavy start.
(d) reversing load and heavy start.