D.c. Motors MCQs

Option A: back e.m.f. is less than the applied voltage

Option B: back e.m.f. is equal to the applied voltage

Option C: back e.m.f. of rotor is more than the applied voltage

Option D: none of the above

Correct Answer: back e.m.f. of rotor is more than the applied voltage ✔

Option A: field control method

Option B: armature controlled method

Option C: field diverter

Option D: frequency control method

Correct Answer: armature controlled method ✔

Option A: Swinburne test

Option B: Hopkinson test

Option C: Brake test

Option D: Field test

Correct Answer: Field test ✔

Option A: decrease in speed

Option B: increase in speed

Option C: short circuit

Option D: open circuit

Correct Answer: increase in speed ✔

Option A: series with field winding

Option B: series speed armature winding

Option C: parallel big field winding

Option D: parallel with armature winding

Correct Answer: series speed armature winding ✔

Option A: not develop starting torque

Option B: fail to start without load

Option C: run at dangerously high speed

Option D: draw more current without producing sufficient torque

Correct Answer: run at dangerously high speed ✔

Option A: voltage control method

Option B: flux control method

Option C: rheostat control method

Option D: all of the above

Correct Answer: all of the above ✔

Option A: decreases

Option B: increases

Option C: remains same

Option D: none of the above

Correct Answer: increases ✔

Option A: decreases

Option B: increases

Option C: remain same

Option D: none of the above

Correct Answer: decreases ✔

Option A: decreases.

Option B: increases

Option C: remain same

Option D: none of the above

Correct Answer: increases ✔

Option A: dc generator

Option B: dc motor

Option C: transformer

Option D: all of the above

Correct Answer: dc motor ✔

Option A: increase in armature current

Option B: increase in flux

Option C: decrease in reactance

Option D: decrease in back emf

Correct Answer: decrease in back emf ✔

A. runs as a generator
B. does not run as a generator
C. also runs as a motor comes to stop after sometime

Correct Answer: runs as a generator ✔

Option A: reducing the field current

Option B: decreasing the armature current

Option C: increasing the armature current

Option D: increasing the excitation current

Correct Answer: reducing the field current ✔

Option A: the field

Option B: the armature

Option C: the brushes

Option D: the commutator

Correct Answer: the armature ✔

Option A: Series motor

Option B: Shunt motor

Option C: Cumulatively compounded motor

Option D: Differentially compounded motor

Correct Answer: Series motor ✔

Option A: series motor

Option B: shunt motor

Option C: compound motor

Option D: any of the above

Correct Answer: compound motor ✔

Option A: series motor

Option B: shunt motor

Option C: compound motor

Option D: any of the above

Correct Answer: series motor ✔

Option A: this will make armature to take heavy current, possibly burning it

Option B: this will result in excessive speed, possibly destroying armature due to excessive centrifugal stresses

Option C: nothing will happen to motor

Option D: motor will come to stop

Correct Answer: this will make armature to take heavy current, possibly burning it ✔

Option A: drum type controller is used

Option B: three point starter is used

Option C: four point starter is used

Option D: all above can be used

Correct Answer: drum type controller is used ✔

Option A: self-induced e.m.f.

Option B: mutually induced e.m.f.

Option C: back e.m.f

Option D: none of the above

Correct Answer: back e.m.f ✔

Option A: a stronger commutating field is needed at low speed than at high speed

Option B: a weaker commutating field is needed at low speed than at high speed

Option C: same commutating field is needed at low speed than at high speed

Option D: none of the above is correct

Correct Answer: a weaker commutating field is needed at low speed than at high speed ✔

Option A: Plugging

Option B: Regenerative braking

Option C: Rheostatic braking

Option D: None of the above

Correct Answer: Plugging ✔

Option A: Shunt motors

Option B: Series motors

Option C: Compound motors

Option D: All of the above

Correct Answer: All of the above ✔

A. motor is run as a generator
B. motor is reversed in direction
C. motor is run at reduced speed

Correct Answer: motor is run as a generator ✔

Option A: no-load

Option B: part load

Option C: full-load

Option D: overload

Correct Answer: full-load ✔

Option A: Swinburne’s test

Option B: Hopkinson’s test

Option C: Field test

Option D: Brake test

Correct Answer: Field test ✔

Option A: stray losses

Option B: eddy current losses

Option C: field copper losses

Option D: windage losses

Correct Answer: stray losses ✔

Option A: iron losses

Option B: line losses

Option C: sparking

Option D: corona losses

Correct Answer: line losses ✔

Option A: yoke

Option B: commutator

Option C: armature conductors

Option D: armature rotor

Correct Answer: armature rotor ✔

Option A: full-load

Option B: rated r.p.m.

Option C: rated voltage

Option D: all of the above

Correct Answer: full-load ✔

Option A: eddy current losses = stray losses

Option B: hysteresis losses = eddy current losses

Option C: copper losses = 0

Option D: variable losses = constant losses

Correct Answer: variable losses = constant losses ✔

Option A: 100 W

Option B: 500 W

Option C: 1000 W

Option D: 1500 W

Correct Answer: 500 W ✔

Option A: Hysteresis losses

Option B: Eddy current losses

Option C: Copper losses

Option D: Windage losses

Correct Answer: Eddy current losses ✔

Option A: Mechanical loss

Option B: Core loss

Option C: Copper loss

Option D: All of the above

Correct Answer: All of the above ✔

Option A: Providing laminations in armature core

Option B: Providing laminations in stator

Option C: Using non-magnetic material for frame

Option D: Using material of low hysteresis co-efficient for armature core material

Correct Answer: Using material of low hysteresis co-efficient for armature core material ✔

Option A: over load relay is connected in series and no volt relay in parallel with the load

Option B: over load relay is connected in parallel and no volt relay in series with the load

Option C: over load relay and no volt relay are both connected in series with the load

Option D: over load relay and no volt relay are both connected in parallel with the load

Correct Answer: over load relay is connected in series and no volt relay in parallel with the load ✔

Option A: trains

Option B: cranes

Option C: hoists

Option D: machine tools

Correct Answer: machine tools ✔

Option A: magnetic field

Option B: active length of the conductor

Option C: current flow through the conductors

Option D: number of conductors

Correct Answer: F. all above factors ✔

Option A: Field copper loss

Option B: Windage loss

Option C: Armature copper loss

Option D: None of the above

Correct Answer: Armature copper loss ✔

Option A: hysteresis loss

Option B: field copper loss

Option C: armature copper loss

Option D: eddy current loss

Correct Answer: armature copper loss ✔

Option A: Loss of efficiency

Option B: Excessive heating of core

Option C: Increase in terminal voltage

Option D: Rise in temperature of ventilating air

Correct Answer: Increase in terminal voltage ✔

Option A: Frequency of magnetic reversals

Option B: Maximum value of flux density

Option C: Volume and grade of iron

Option D: Rate of flow of ventilating air

Correct Answer: Rate of flow of ventilating air ✔

Option A: high initial cost

Option B: high maintenance cost

Option C: low efficiency at Hght loads

Option D: all of the above

Correct Answer: all of the above ✔

Option A: residual magnetism of the generator

Option B: core losses of motor

Option C: mechanical losses of motor and generator together

Option D: all of the above

Correct Answer: residual magnetism of the generator ✔

Option A: Field control

Option B: Armature voltage control

Option C: Shunt armature control

Option D: Mechanical loading system

Correct Answer: Armature voltage control ✔

Option A: voltage control method

Option B: field divertor method

Option C: field control method

Option D: armature resistance control method

Correct Answer: voltage control method ✔

Option A: Series motor

Option B: Shunt motor

Option C: Cumulatively compounded motor

Option D: Differentially compounded motor

Correct Answer: Series motor ✔

Option A: D.C. shunt motor

Option B: D.C. series motor

Option C: Induction motor

Option D: Reluctance motor

Correct Answer: Reluctance motor ✔

Option A: D.C. shunt motor

Option B: D.C. series motor

Option C: Single phase induction motor (split phase start or induction run motor)

Option D: Reluctance motor

Correct Answer: Single phase induction motor (split phase start or induction run motor) ✔

Option A: Torque and speed are inversely proportional to armature current

Option B: Torque is proportional to armature current

Option C: Torque is proportional to square root of armature current

Option D: The speed is inversely proportional to the torque and the torque is proportional to square of armature current

Correct Answer: The speed is inversely proportional to the torque and the torque is proportional to square of armature current ✔

Option A: increase

Option B: decrease

Option C: remain same

Option D: become zero

Correct Answer: increase ✔

Option A: D.C. shunt motor

Option B: D.C. series motor

Option C: Universal motor

Option D: Synchronous motor

Correct Answer: Synchronous motor ✔

Option A: regenerative

Option B: plugging

Option C: dynamic braking

Option D: none of the above

Correct Answer: plugging ✔

Option A: of lower H.P. should be selected

Option B: of higher H.P. should be selected

Option C: can be used for 50°C ambient temperature also

Option D: is to be derated by a factor recommended by manufacturer and select the next higher H.P. motor

Correct Answer: is to be derated by a factor recommended by manufacturer and select the next higher H.P. motor ✔

Option A: constant voltage drive

Option B: constant current drive

Option C: constant torque drive

Option D: none of the above

Correct Answer: constant torque drive ✔

Option A: zero torque braking

Option B: smallest torque braking

Option C: highest torque braking

Option D: none of the above

Correct Answer: highest torque braking ✔

Option A: torque will remain constant

Option B: torque will change but power will remain constant

Option C: torque and power both will change

Option D: torque, power and speed, all will change

Correct Answer: torque will change but power will remain constant ✔

Option A: Differentially compounded motor

Option B: Cumulatively compounded motor

Option C: Shunt motor

Option D: Series motor

Correct Answer: Series motor ✔

Option A: independent of Ia

Option B: proportional to la

Option C: varies as (Ia)

Option D: varies as la

Correct Answer: independent of Ia ✔

Option A: increasing the resistance in armature circuit

Option B: increasing the resistance in field circuit

Option C: reducing the resistance in the field circuit

Option D: reducing the resistance in the armature circuit

Correct Answer: increasing the resistance in field circuit ✔

Option A: a resistance is connected in series with armature

Option B: a resistance is connected parallel to the armature

Option C: armature is temporarily open circuited

Option D: a high value resistor is connected across the field winding

Correct Answer: a resistance is connected in series with armature ✔

Option A: constant torque drive

Option B: constant voltage drive

Option C: constant current drive

Option D: none of the above

Correct Answer: constant torque drive ✔

Option A: 2.36%

Option B: 4.76%

Option C: 6.77%

Option D: 8.84%

Correct Answer: 4.76% ✔

Option A: centrifugal pumps

Option B: elevators

Option C: steel rolling mills

Option D: colliery winders

Correct Answer: colliery winders ✔

Option A: Voltage control method

Option B: Field control method

Option C: Armature control method

Option D: All above methods

Correct Answer: Armature control method ✔

Option A: field flux only

Option B: armature current only

Option C: both A. and B.

Option D: none of the above

Correct Answer: armature current only ✔

Option A: reduce slightly

Option B: increase slightly

Option C: increase proportionately

Option D: remains unchanged

Correct Answer: reduce slightly ✔

Option A: Shunt motor

Option B: Series motor

Option C: Differential compound motor

Option D: Cumulative compound motor

Correct Answer: Series motor ✔

Option A: D.C. series motor

Option B: D.C. shunt motor

Option C: induction motor

Option D: all of above motors

Correct Answer: A. D.C. series motor ✔

Option A: the motor will first stop and then run in opposite direction as series motor

Option B: the motor will work as series motor and run at slow speed in the same direction

Option C: the motor will work as series motor and run at high speed in the same direction

Option D: the motor will not work and come to stop

Correct Answer: the motor will first stop and then run in opposite direction as series motor ✔

Option A: Single phase capacitor start

Option B: Induction motor

Option C: Synchronous motor

Option D: D.C. motor

Correct Answer: D. D.C. motor ✔

Option A: level compounded

Option B: under compounded

Option C: cumulatively compounded

Option D: differentially compounded

Correct Answer: cumulatively compounded ✔

Option A: in one direction

Option B: in both directions

Option C: below normal speed only

Option D: above normal speed only

Correct Answer: in both directions ✔

Option A: it increases the input power con-sumption

Option B: commutator gets damaged

Option C: both A. and B.

Option D: none of the above

Correct Answer: commutator gets damaged ✔

Option A: series motor only

Option B: shunt motor only

Option C: compound motor only

Option D: both shunt and compound motor

Correct Answer: both shunt and compound motor ✔

Option A: Series motor

Option B: Shunt motor

Option C: Cumulatively compounded motor

Option D: Differentially compounded motor

Correct Answer: Series motor ✔

Option A: 2 to 3 per cent

Option B: 10 to 15 per cent

Option C: 20 to 25 per cent

Option D: 50 to 75 per cent

Correct Answer: 2 to 3 per cent ✔

Option A: Low speed operation

Option B: High speed operation

Option C: Variable speed operation

Option D: Fixed speed operation

Correct Answer: Variable speed operation ✔

Option A: back e.m.f. = 2 x supply voltage

Option B: back e.m.f. = | x supply voltage

Option C: supply voltage = | x back e.m.f

Option D: supply voltage = back e.m.f

Correct Answer: back e.m.f. = | x supply voltage ✔

Option A: 4.0

Option B: 2.0

Option C: 1.0

Option D: 0.5

Correct Answer: 0.5 ✔

Option A: To reduce eddy current loss

Option B: To support the field coils

Option C: To spread out flux for better uniformity

Option D: To reduce the reluctance of the magnetic path

Correct Answer: To reduce eddy current loss ✔

Option A: Starting torque

Option B: Operating speed

Option C: Full-load current

Option D: All of the above

Correct Answer: Full-load current ✔

Option A: Series motor

Option B: Shunt motor

Option C: Air motor

Option D: Battery operated motor

Correct Answer: Air motor ✔

Option A: damage to commutator segments

Option B: damage to commutator insulation

Option C: increased power consumption

Option D: all of the above

Correct Answer: all of the above ✔

Option A: as separately wound unit

Option B: in parallel with armature winding

Option C: in series with armature winding

Option D: in parallel with field winding

Correct Answer: in series with armature winding ✔

Option A: shunt

Option B: series

Option C: differentially compounded

Option D: cumulativelyc’ompounded

Correct Answer: differentially compounded ✔

Option A: where load is constant

Option B: where load changes frequently

Option C: where constant operating speed is needed

Option D: in none of the above situations

Correct Answer: in none of the above situations ✔

A. nothing will happen to the motor
B. this will make armature to take heavy current, possibly burning it
C. this will result in excessive speed, possibly destroying armature due to excessive centrifugal stresses D. motor will run at very slow speed

Correct Answer: C. this will result in excessive speed, possibly destroying armature due to excessive centrifugal stresses D. motor will run at very slow speed ✔

Option A: Series motor

Option B: Shunt motor

Option C: Cumulatively compounded motor

Option D: Differentially compounded motor

Correct Answer: Cumulatively compounded motor ✔

Option A: Series motor

Option B: Shunt motor

Option C: Cumulatively compounded ‘motor

Option D: Differentially compounded motor

Correct Answer: Differentially compounded motor ✔

Option A: the power drawn in kW

Option B: the power drawn in kVA

Option C: the gross power

Option D: the output power available at the shaft

Correct Answer: the output power available at the shaft ✔

Option A: the torque required

Option B: the speed of the motor

Option C: the voltage across the terminals

Option D: none of the above

Correct Answer: the torque required ✔

Option A: 100% of the previous value

Option B: 50% of the previous value

Option C: 25% of the previous value

Option D: 10% of the previous value

Correct Answer: 25% of the previous value ✔

Option A: proportional to the armature current

Option B: proportional to the square of the armature current

Option C: proportional to field current

Option D: inversely proportional to the armature current

Correct Answer: proportional to the armature current ✔

Option A: low

Option B: around 500 Q

Option C: 1000 Q

Option D: infinitely large

Correct Answer: low ✔

Option A: Blowers

Option B: Conveyors

Option C: Air compressors

Option D: Centrifugal pumps

Correct Answer: Conveyors ✔

Option A: Lenz’s law

Option B: Faraday’s law

Option C: Coloumb’s law

Option D: Fleming’s left-hand rule

Correct Answer: Fleming’s left-hand rule ✔

Option A: Slip rings

Option B: Commutator

Option C: Field winding

Option D: Armature winding

Correct Answer: Field winding ✔

Option A: series motors

Option B: shunt motors

Option C: compound motors

Option D: none of the above

Correct Answer: shunt motors ✔