 # DC Motor MCQ Questions & Answers ### 1.In the block diagram of a separately excited dc motor how does the armature induced emf appear as?

• APositive feedback
• BNegative feedback
• CDisturbance input
• DOutput
Correct Answer : (B)

Negative feedback

Explanation:

### 2.In a dc motor energy conversion would not have been possible but for

• AInput energy from the supply
• BProduction of back emf in the armature
• CUse of commutator
• DRotation of the machine
Correct Answer : (B)

Production of back emf in the armature

Explanation:

### 3.The current drawn by a 120 V dc motor with back emf of 110 V and armature resistance of 0.4 ohm is

• A4 A
• B25 A
• C275 A
• D300 A
Correct Answer : (B)

25 A

Explanation:

The current drawn by a 120 V dc motor with back emf of 110 V and armature resistance of 0.4 ohm is 25 A.

### 4.A 220 V dc machine has an armature resistance of 1 ohm. If the full load current is 20 A , the difference of induced voltage, when the machine is running as a motor and generator is

• A20 V
• B0 V
• C40 V
• D60 V
Correct Answer : (C)

40 V

Explanation:

### 5.The current drawn by a 220 V dc motor of armature resistance 0.5 ohm and back emf 200V is

• A40 A
• B44 A
• C400 A
• D440 A
Correct Answer : (A)

40 A

Explanation:

### 6.With the increase in speed of a dc motor

• ABoth back emf as well as line current increase
• BBoth back emf as well as line current fall
• CBack emf increases but line current falls
• DBack emf falls and line current increases
Correct Answer : (C)

Back emf increases but line current falls

Explanation:

### 7.If the back in a dc motor vanishes suddenly, the motor will

• AStart hunting
• BBurn
• CRun at very high speed
• DRun at very slow speed
Correct Answer : (B)

Burn

Explanation:

If the back in a dc motor vanishes suddenly, the motor will burn.

### 8.The output power of any electrical motor is taken from the

• AArmature
• BField
• CCoupling mounted on the shaft
• DMotor frame
Correct Answer : (C)

Coupling mounted on the shaft

Explanation:

### 9.The armature shaft must be able to withstand

• AAny unbalanced magnetic pull on the armature core
• BTwisting strains due to transmission of torque
• CBending moment due to weight of the armature and commutator
• DAll of the above
Correct Answer : (D)

All of the above

Explanation:

### 10.The output indicated on the name plate of any motor is always the

• AGross power
• BPower drawn in kVA
• CPower drawn in kW
• DOutput power at the shaft
Correct Answer : (D)

Output power at the shaft

Explanation:

The output indicated on the name plate of any motor is always the  Output power at the shaft.

### 11.A thicker wire is used in dc series motor filed winding than that in a dc shunt motor.

• ATo create more flux
• BTo reduce resistance
• CTo carry large load current
• DBoth (b) and (c)
Correct Answer : (D)

Both (b) and (c)

Explanation:

A thicker wire is used in dc series motor filed winding than that in a dc shunt motor To reduce resistance and to carry large load current.

### 12.In case of a conductively compensated dc series motor, the compensating winding is provided

• AIn series with the armature winding
• BIn parallel with the armature winding
• CIn parallel with the field winding
• DAs a separate unit
Correct Answer : (A)

In series with the armature winding

Explanation:

In case of a conductively compensated dc series motor, the compensating winding is provided In series with the armature winding.

### 13.The dc compounded motors are generally

• ALevel compounded
• BCumulative compounded
• CDifferential compounded
• DNone of these
Correct Answer : (B)

Cumulative compounded

Explanation:

The dc compounded motors are generally Cumulative compounded motor.

### 14.In a dc compound motor, the filed regulator is provided to

• AControl the flux
• BLimit the armature current
• CDemagnetize filed partially
• DNone Of the above
Correct Answer : (A)

Control the flux

Explanation:

In a dc compound motor, the filed regulator is provided to Control the flux.

### 15.The direction of rotation of a dc motor can be determined by

• AFleming?s right-hand rule
• BFleming left hand rule
• CLenz?s law
• DAmpere law
Correct Answer : (B)

Fleming left hand rule

Explanation:

The direction of rotation of a dc motor can be determined by Fleming left hand rule.

### 16.The direction of rotation of a dc shunt motor can be reversed by interchanging

• AThe supply terminals
• BThe filed terminals only
• CThe armature terminals only
• DEither field or armature terminals
Correct Answer : (D)

Either field or armature terminals

Explanation:

The direction of rotation of a dc shunt motor can be reversed by interchanging Either field or armature terminals.

### 17.When the supply terminals of a dc shunt motor are interchanged

• AThe motor will stop
• BThe motor will run at its normal speed in the same direction as before
• CThe direction of rotation will reverse
• DThe motor will run much faster in the same direction
Correct Answer : (B)

The motor will run at its normal speed in the same direction as before

Explanation:

When the supply terminals of a dc shunt motor are interchanged, the motor will run at its normal speed in the same direction as before.

### 18.The direction of rotation of a dc series motor can be reversed

• ABy interchanging supply terminals
• BBy interchanging field terminals
• CEither by interchanging supply terminals or by interchanging field terminals
• DBy interchanging supply terminals as well as field terminals
Correct Answer : (B)

By interchanging field terminals

Explanation:

The direction of rotation of a dc series motor can be reversed By interchanging field terminals.

### 19.The speed of a dc motor is

• Adirectly proportional to back emf and flux
• Bdirectly proportional to it back emf and inversely proportional to flux
• Cinversely proportional to both back emf and flux
• Ddirectly proportional to flux and inversely proportional to back emf
Correct Answer : (B)

directly proportional to it back emf and inversely proportional to flux

Explanation:

The speed of a dc motor is directly proportional to it back emf and inversely proportional to flux.

### 20.If the load current and flux of a dc motor are held constant and voltage applied across it armature is increased by 54%, the speed of the motor will

• Aincrease by 5%
• Breduce by 5%
• Cremain un-alternated
• Ddepends on other factors
Correct Answer : (A)

increase by 5%

Explanation: