Eddy current loss in armature core can be reduced by

 Q651. In a DC machine, armature reaction causes

A) Increased main flux
B) Distortion of main field flux
C) Uniform air gap flux
D) No effect
Ans: B

Q652. Interpoles in DC machines are connected in
A) Series with armature
B) Parallel with armature
C) Series with shunt field
D) Parallel with shunt field
Ans: A

Q653. The main purpose of a commutator in a DC generator is
A) To convert DC into AC
B) To convert AC into DC
C) To increase voltage
D) To reduce eddy current
Ans: B

Q654. The armature of a DC machine is laminated to
A) Reduce hysteresis loss
B) Reduce eddy current loss
C) Increase flux
D) Strengthen armature
Ans: B

Q655. If the speed of a DC generator increases, its generated EMF
A) Decreases
B) Increases
C) Remains same
D) Becomes zero
Ans: B

Q656. In a DC shunt generator, the voltage drops to zero when
A) Load increases
B) Field circuit opens
C) Armature speed decreases
D) Brush contact improves
Ans: B

Q657. A cumulatively compounded DC motor is preferred for
A) Constant speed operation
B) Variable load with heavy starting torque
C) Light load
D) High-speed operation
Ans: B

Q658. The commutation in DC machine is improved by
A) Increasing armature resistance
B) Decreasing brush contact area
C) Using interpoles
D) Decreasing field current
Ans: C

Q659. The mechanical power developed in a DC motor is maximum when
A) Back emf is half of supply voltage
B) Back emf equals supply voltage
C) Armature current is maximum
D) Field current is zero
Ans: A

Q660. The direction of rotation of a DC motor can be reversed by
A) Changing armature connections
B) Changing field connections
C) Changing either field or armature connections
D) Changing both simultaneously
Ans: C

Q661. In a DC machine, the function of brushes is to
A) Conduct current to commutator
B) Conduct current to field winding
C) Increase magnetic flux
D) Cool the armature
Ans: A

Q662. The armature reaction in a DC generator causes
A) Neutral plane shift
B) Increase in flux
C) Voltage rise
D) Field strengthening
Ans: A

Q663. The losses in a DC generator are
A) Constant losses only
B) Variable losses only
C) Constant + variable losses
D) Core losses only
Ans: C

Q664. For maximum efficiency of a DC generator,
A) Variable losses = constant losses
B) Variable losses > constant losses
C) Variable losses < constant losses
D) Constant losses = 0
Ans: A

Q665. The back emf in a DC motor is proportional to
A) Armature current
B) Field flux
C) Speed
D) Product of field flux and speed
Ans: D

Q666. The speed of a DC shunt motor can be controlled by
A) Armature resistance control
B) Field flux control
C) Voltage control
D) All of the above
Ans: D

Q667. The torque of a DC motor is directly proportional to
A) Armature current only
B) Field flux only
C) Product of flux and armature current
D) Speed
Ans: C

Q668. The armature current in a DC motor is maximum when
A) Motor starts
B) Motor runs at full speed
C) Motor runs at no load
D) Field is open
Ans: A

Q669. Sparking at brushes in DC machine can be reduced by
A) Decreasing brush pressure
B) Using interpoles
C) Using carbon brushes only
D) Reducing speed
Ans: B

Q670. In a DC generator, residual magnetism helps in
A) Commutation
B) Self-excitation
C) Cooling
D) Armature reaction
Ans: B

Q671. The type of DC generator used for arc welding is
A) Shunt generator
B) Series generator
C) Compound generator
D) Differential generator
Ans: B

Q672. Armature reaction in DC machine results in
A) Flux strengthening
B) Cross magnetization
C) Constant flux
D) Improved commutation
Ans: B

Q673. The lap winding in DC machine is used for
A) High voltage, low current
B) Low voltage, high current
C) High speed
D) High efficiency
Ans: B

Q674. A wave wound DC machine is used for
A) Low voltage
B) High current
C) High voltage, low current
D) Low speed
Ans: C

Q675. In a DC shunt generator, voltage builds up only if
A) Residual magnetism is present
B) Field resistance < critical resistance
C) Speed > critical speed
D) All of the above
Ans: D

Q676. The purpose of compensating winding is
A) To reduce armature reaction
B) To increase flux
C) To increase efficiency
D) To improve voltage regulation
Ans: A

Q677. In a DC motor, if field current increases, speed
A) Increases
B) Decreases
C) Remains constant
D) Becomes zero
Ans: B

Q678. When a DC motor is overloaded, it will
A) Run faster
B) Slow down
C) Stop immediately
D) Speed up then stop
Ans: B

Q679. A DC motor converts
A) Electrical energy into mechanical energy
B) Mechanical energy into electrical energy
C) AC to DC
D) DC to AC
Ans: A

Q680. In a DC generator, generated EMF is directly proportional to
A) Flux
B) Speed
C) Flux × Speed
D) Armature current
Ans: C

Q681. In a DC shunt motor, speed is nearly constant because
A) Flux is constant
B) Armature current is constant
C) Field current varies
D) Torque is constant
Ans: A

Q682. The field winding of a DC shunt motor is made of
A) Thick wire
B) Thin wire
C) Aluminum wire
D) Iron wire
Ans: B

Q683. The series field winding in a DC motor carries
A) Full armature current
B) Half armature current
C) No current
D) Shunt current
Ans: A

Q684. For regenerative braking,
A) Motor acts as generator
B) Motor runs faster
C) Motor absorbs energy
D) Motor reverses polarity
Ans: A

Q685. The main advantage of DC series motor is
A) High starting torque
B) Constant speed
C) Low cost
D) No commutation problem
Ans: A

Q686. The direction of rotation of a DC motor is given by
A) Fleming’s left-hand rule
B) Fleming’s right-hand rule
C) Lenz’s law
D) Faraday’s law
Ans: A

Q687. A differential compound motor is never used for
A) Variable load
B) Heavy torque
C) Industrial drives
D) Hoisting applications
Ans: D

Q688. The copper losses in a DC motor depend on
A) Field current
B) Armature current
C) Both A and B
D) Speed
Ans: C

Q689. Armature reaction is more in
A) Loaded condition
B) No-load condition
C) Open circuit
D) Short circuit
Ans: A

Q690. The commutator converts
A) DC to AC
B) AC to DC
C) DC to DC
D) AC to AC
Ans: B

Q691. The sparkless commutation is achieved by
A) Interpoles
B) Resistance in armature
C) Large brushes
D) Field weakening
Ans: A

Q692. The brush contact drop in DC machine is about
A) 0.2–0.4 V per brush
B) 1 V per brush
C) 2 V per brush
D) 5 V per brush
Ans: A

Q693. The efficiency of large DC machine is in the range of
A) 40–50%
B) 60–70%
C) 80–90%
D) 90–95%
Ans: D

Q694. In DC generator, open circuit characteristic shows relation between
A) Voltage and current
B) Voltage and field current
C) Current and speed
D) Speed and torque
Ans: B

Q695. The induced EMF in a DC generator is due to
A) Electrostatic induction
B) Electromagnetic induction
C) Mechanical action
D) Chemical reaction
Ans: B

Q696. In a DC shunt motor, if supply voltage decreases, speed
A) Increases
B) Decreases
C) Remains same
D) Becomes zero
Ans: B

Q697. The function of equalizer rings in DC machine is to
A) Prevent circulating current
B) Improve commutation
C) Increase voltage
D) Increase torque
Ans: A

Q698. Eddy current loss in armature core can be reduced by
A) Laminating core
B) Increasing speed
C) Using copper core
D) Using solid iron core
Ans: A

Q699. The critical speed in DC generator is that speed at which
A) Voltage just builds up
B) Maximum voltage occurs
C) Minimum voltage occurs
D) No load current is zero
Ans: A

Q700. The commutation in DC machine is the process of
A) Current reversal in armature coil
B) Voltage reversal in field
C) Flux reversal in core
D) Torque reversal
Ans: A