For higher voltage, which winding is preferred?

 401. The direction of rotation of a DC motor depends upon

A) Direction of current in armature and field
B) Supply voltage magnitude
C) Load torque
D) Armature resistance
Ans: A

402. When load on a DC shunt motor increases, the armature current
A) Increases
B) Decreases
C) Remains constant
D) Becomes zero
Ans: A

403. The voltage drop across brushes depends on
A) Brush contact material
B) Speed
C) Field current
D) Armature reaction
Ans: A

404. The main advantage of a compound motor is
A) Good starting torque and speed regulation
B) Low cost
C) Constant speed only
D) Simple control
Ans: A

405. In DC generator, the open-circuit characteristic is plotted between
A) Field current and generated emf
B) Armature current and emf
C) Speed and emf
D) Flux and current
Ans: A

406. The commutation is said to be good when
A) There is no sparking
B) Sparking is heavy
C) Brushes are hot
D) Resistance increases
Ans: A

407. In DC machine, armature reaction distorts
A) The main field flux
B) The armature field
C) The commutator
D) The brush voltage
Ans: A

408. A DC motor can be used as a generator when
A) Driven mechanically
B) Speed increases
C) Field is opened
D) Brushes removed
Ans: A

409. A separately excited generator can also work as
A) DC motor
B) Transformer
C) Alternator
D) Induction motor
Ans: A

410. In a DC generator, the number of poles affects
A) Frequency of generated emf
B) Commutation
C) Both A and B
D) Only field flux
Ans: C

411. The insulation between commutator segments is provided by
A) Mica
B) Paper
C) Varnish
D) Cotton
Ans: A

412. The direction of induced emf can be found by
A) Fleming’s right-hand rule
B) Fleming’s left-hand rule
C) Lenz’s law
D) Maxwell’s rule
Ans: A

413. In DC motor, if load increases, back emf
A) Decreases
B) Increases
C) Remains constant
D) Becomes zero
Ans: A

414. The most suitable DC motor for cranes is
A) DC series motor
B) DC shunt motor
C) DC compound motor
D) Separately excited motor
Ans: A

415. The function of a starter in a DC motor is to
A) Limit starting current
B) Control speed
C) Increase torque
D) Reduce sparking
Ans: A

416. A 3-point starter cannot be used with
A) DC shunt motor having field weakening
B) DC series motor
C) Compound motor
D) Shunt motor with constant field
Ans: A

417. The overload protection in DC starter is provided by
A) No-volt coil
B) Overload release coil
C) Armature resistance
D) Fuse
Ans: B

418. The no-volt coil in a DC starter ensures that
A) Motor is disconnected if supply fails
B) Motor runs at constant speed
C) Torque is constant
D) Armature resistance remains fixed
Ans: A

419. A 4-point starter is used when
A) Field weakening is required
B) Constant speed is needed
C) Load torque is high
D) Motor is compound
Ans: A

420. The field winding of a DC shunt motor is connected
A) Parallel to armature
B) Series with armature
C) Across commutator
D) Across brushes
Ans: A

421. The starting current of a DC motor is limited by
A) Starter resistance
B) Field resistance
C) Armature reaction
D) Commutator drop
Ans: A

422. In a DC motor, the relation between back emf and supply voltage is
A) V = Eb + IaRa
B) V = Eb – IaRa
C) Eb = V + IaRa
D) Eb = IaRa
Ans: A

423. The speed of a DC motor can be increased by
A) Reducing field flux
B) Increasing armature voltage
C) Both A and B
D) Increasing load torque
Ans: C

424. Which DC motor is preferred for constant speed?
A) Shunt motor
B) Series motor
C) Compound motor
D) Differential motor
Ans: A

425. Which motor has the highest starting torque?
A) DC series motor
B) DC shunt motor
C) Compound motor
D) Synchronous motor
Ans: A

426. The speed of DC series motor is
A) Inversely proportional to flux
B) Directly proportional to flux
C) Independent of flux
D) Constant
Ans: A

427. The field winding of a DC series motor is made of
A) Thick wire, few turns
B) Thin wire, many turns
C) Thick wire, many turns
D) Thin wire, few turns
Ans: A

428. The back emf in a DC motor acts in
A) Opposition to supply voltage
B) Same direction as supply voltage
C) Direction of flux
D) Direction of torque
Ans: A

429. In a DC generator, the emf is induced because of
A) Rate of change of flux linkage
B) Magnetic reluctance
C) Constant current
D) Constant field
Ans: A

430. For a DC generator, emf increases with
A) Speed
B) Flux
C) Both speed and flux
D) Armature resistance
Ans: C

431. The terminal voltage of DC generator decreases with load because of
A) Armature reaction and IR drop
B) Speed increase
C) Field weakening
D) All of these
Ans: A

432. The load characteristic of a DC shunt generator is
A) Drooping
B) Flat
C) Rising
D) Parabolic
Ans: A

433. The losses in DC machines are classified as
A) Copper, iron, and mechanical losses
B) Magnetic and electric losses
C) Fixed and variable losses
D) Both A and C
Ans: D

434. The armature current of a DC generator is equal to
A) IL + If
B) IL – If
C) V / R
D) Ia = IL
Ans: A

435. In a short-shunt compound generator, the shunt field is connected across
A) Armature
B) Series field
C) Load
D) Both armature and load
Ans: A

436. In a long-shunt compound generator, shunt field is connected across
A) Series field and armature
B) Armature only
C) Series field only
D) Load only
Ans: A

437. If a generator fails to build up voltage, it may be due to
A) No residual magnetism
B) Wrong field connection
C) High field resistance
D) All of these
Ans: D

438. The iron losses in DC machines are composed of
A) Hysteresis and eddy current losses
B) Friction losses
C) Magnetic losses
D) Armature reaction losses
Ans: A

439. To reduce hysteresis loss, material with
A) Low hysteresis coefficient
B) High permeability
C) High coercivity
D) Large loop area
Ans: A

440. To reduce eddy current losses
A) Core is laminated
B) Resistance is reduced
C) Flux is increased
D) Field is strengthened
Ans: A

441. The brushes of DC machine should be placed on
A) Magnetic neutral axis
B) Geometrical neutral axis
C) At 45°
D) Along pole axis
Ans: A

442. The interpoles are connected in
A) Series with armature
B) Parallel with armature
C) Series with field
D) Parallel with field
Ans: A

443. The interpoles are provided to
A) Improve commutation
B) Reduce losses
C) Increase voltage
D) Increase torque
Ans: A

444. The number of brushes in DC machine depends on
A) Current capacity
B) Number of poles
C) Both A and B
D) Armature resistance
Ans: C

445. For higher voltage, which winding is preferred?
A) Wave winding
B) Lap winding
C) Duplex winding
D) Both A and B
Ans: A

446. For higher current, which winding is used?
A) Lap winding
B) Wave winding
C) Spiral winding
D) Duplex wave
Ans: A

447. In DC machines, commutation is the process of
A) Reversal of current in armature coil
B) Reversal of field current
C) Voltage transformation
D) Power conversion
Ans: A

448. The brush contact drop in DC machine is about
A) 1–2 V
B) 5 V
C) 10 V
D) 0.5 V
Ans: A

449. In differential compound motor, the speed
A) Increases with load
B) Decreases with load
C) Remains constant
D) Varies randomly
Ans: A

450. Which type of DC motor is suitable for elevators?
A) Cumulative compound motor
B) Shunt motor
C) Series motor
D) Differential compound motor
Ans: A