501 MCQ Questions on DC Machine

401. For constant torque drive which speed control method is preferred? [DSSB – 2015]

(a) Field control
(b) Armature voltage control
(c) Shunt armature control
(d) Mechanical loading system

402. Armature reaction in DC motor results

(a) decrease in speed.
(b) increase in speed.
(c) short circuit.
(d) open circuit. [MPJE – 2015]

403. In shunt de motor the direction of rotation of the motor will reversed, when

(a) either field terminals are reversed or armature terminals are reversed.
(b) only armature terminals are reversed.
(c) only field terminals are changed.
(d) none of the above. [MP JE – 2015]

404. For lifts, which of the following types of D.C. motor is used?

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

405. With 100% inductive shunt compensation, the voltage profile is flat for

(a) 100% loading of line.
(b) 50% loading of line.
(c) Zero loading of line.
(d) None of these.

406. The cross-section of conductors for large sizes DC machines are

(a) circular.
(b) rectangular.
(c) triangular.
(d) trapezoidal.

407. Magnetic cores are made up of thin lightly insulated lamination to reduce

(a) power factor.
(b) hysteresis loss.
(c) load loss.
(d) eddy current loss. [UPSSSC – 2015]

408. In DC machines the value of A equals to 2

(a) for lap winding.
(b) for wave winding.
(c) for field winding.
(d) for armature winding. [UPSSC – 2015]

409. Separately excited and self-excited are types of which machine?

(a) dc machine.
(b) synchronous machine.
(c) induction machine.
(d) none of the above.
[UPSSSC – 2015]

410. Armature reaction of an unsaturated DC machine is

(a) cross magnetizing.
(b) demagnetizing.
(c) magnetizing.
(d) none of the above. [UPSSSC – 2015]

411. For high values of armature current, the speed of a DC series motor is

(a) proportional to armature current.
(b) inversely proportional to armature current.
(c) constant.
(d) none of these. [MP JE 2016]

412. If flux of dc series motor reduces, its speed will be

(a) be infinity.
(b) be zero.
(c) be between zero and infinity.
(d) constant. [MP JE – 2016]

413. The disadvantages of machine commutation are

(a) large machine size.
(b) restriction of the speed range.
(c) both of the above.
(d) None of the above. [MP JE 2016]

414. Variable speed cannot be obtained with

(a) dc motors controller.
(b) derivative controller.
(c) soft starter controller.
(d) ac and dc controllers. [MP JE – 2016]

415. The construction of DC motor is

(a) same as that of dc generator.
(b) different than dc generator.
(c) similar but different in frame construction.
(d) different in construction and similar in frame construction.

416. A starter is necessary to start a dc motor because

(a) it is used to start a dc motor.
(b) it restricts the speed of the motor.
(c) it limits the back e.m.f. to a safe value.
(d) it limits the starting current to a safe value.

417. What happens if the field windings of a running shunt motor suddenly break open? [MP JE 2016]

(a) Its speed slows down.
(b) Its speed becomes dangerously high.
(c) It gives out sparks.
(d) It stops at once.

418. If speed of a d.c. shunt motor increases, the back emf

(a) increases.
(b) decreases.
(c) remains fixed.
(d) decreases and then increases.

419. In a d.c. machine without inter-poles, to get commutation improved, the brush shift angle must be

(a) varied with change in load.
(b) kept constant.
(c) zero degree.
(d) none of these.

420. Application of DC motors is generally restricted to a few load speed applications. It is due to which of the following factors? [MP JE 2016]

(a) The cost of the motor.
(b) The problems with mechanical commutation.
(c) The maintenance problems.
(d) None of these.

421. By providing a variable resistance across the series field (diverter) in a dc series motor, speeds above normal can be obtained because

(a) armature current decreases.
(b) flux is reduced.
(c) line current is decreased.
(d) none of these.

422. Electrical machines are designed to have the maximum efficiency at

(a) full load.
(b) 50% of full load.
(c) near about full load.
(d) no load. [MP JE 2016]

423. In dc machines, the

(a) torque and induced e.m.f. are produced both in motor and generator.
(b) torque is produced in motor and e.m.f. is in generator.
(c) torque is produced in generator and e.m.f. is in motor.
(d) none of these. [MP JE – 2016]

424. Which part of DC machines converts the alternating current induced in armature conductors into unidirectional current in the external load circuit? [MP JE – 2016]

(a) Commutator
(c) Armature core
(d) Armature windings
(b) Pole coils

425. Fly wheel is mounted on the motor shaft in …………. motor. [MP JE – 2016]

(a) compound
(b) simple
(c) variable
(d) complex

426. In a six pole motor, 4 mechanical degrees is equal to

(a) 4 electrical degrees.
(b) 2 electrical degrees.
(c) 8 electrical degrees.
(d) 12 electrical degrees. [Uttarakhand 2013]

427. An electric train employing a d.c. series motor is running at a fixed speed. When a sudden drop in voltage of supply takes place, then this results in

(a) drop in speed and rise in current.
(b) rise in speed and drop in current.
(c) rise in speed and rise in current.
(d) drop in speed with current unaltered.

428. A d.c. series motor has linear magnetization characteristics and negligible armature resistance. The motor speed is

(a) directly proportional to √T
(b) inversely proportional to √T
(c) directly proportional to T
(d) inversely proportional to T