The cause of sparking at brushes may be

 Q701. The armature winding of a DC machine is placed on the

A) Stator
B) Rotor
C) Field poles
D) Yoke
Ans: B

Q702. The field winding of a DC machine is generally placed on the
A) Armature
B) Rotor
C) Stator
D) Commutator
Ans: C

Q703. The insulation between the commutator segments is made of
A) Mica
B) Paper
C) Plastic
D) Rubber
Ans: A

Q704. The function of a brush holder is to
A) Insulate the brushes
B) Hold the brushes against the commutator
C) Supply field current
D) Reduce eddy currents
Ans: B

Q705. The armature reaction in a DC machine reduces
A) Terminal voltage
B) Armature current
C) Field current
D) Power output
Ans: A

Q706. The number of commutator segments in a DC machine is equal to
A) Number of armature conductors
B) Number of armature coils
C) Half the number of armature conductors
D) Twice the number of armature coils
Ans: B

Q707. In DC generators, the brushes are placed along the
A) Geometrical neutral axis
B) Magnetic neutral axis
C) Axis of poles
D) Armature slot axis
Ans: B

Q708. The magnetic field in a DC machine is produced by
A) Armature winding
B) Field winding
C) Commutator
D) Brushes
Ans: B

Q709. In DC shunt motors, speed decreases slightly with load due to
A) Armature reaction
B) Field weakening
C) Increased back emf
D) High resistance
Ans: A

Q710. A DC series motor should never be started
A) With load
B) Without load
C) With low voltage
D) With weak field
Ans: B

Q711. The neutral plane in a DC generator is shifted because of
A) Armature reaction
B) Commutation
C) Magnetic leakage
D) Eddy currents
Ans: A

Q712. The purpose of interpoles is to produce
A) Cross-magnetizing flux
B) Demagnetizing flux
C) Neutralizing flux
D) Strengthening flux
Ans: C

Q713. The brushes in DC machines are made of
A) Copper
B) Carbon or graphite
C) Steel
D) Aluminum
Ans: B

Q714. The voltage regulation of a DC generator is the measure of
A) Efficiency
B) Change in voltage with load
C) Power factor
D) Speed regulation
Ans: B

Q715. The load characteristic of a DC shunt generator is
A) Rising
B) Drooping
C) Flat
D) Non-linear
Ans: B

Q716. The efficiency of a DC generator is maximum when
A) Iron losses = copper losses
B) Variable losses = constant losses
C) Copper losses = friction losses
D) Iron losses = friction losses
Ans: B

Q717. The speed-torque characteristic of a DC series motor is
A) Linear
B) Hyperbolic
C) Parabolic
D) Exponential
Ans: B

Q718. The speed control of DC shunt motor by armature voltage variation gives
A) Speed below normal
B) Speed above normal
C) Constant torque
D) None
Ans: A

Q719. The field control method in DC motor gives
A) Speed above normal
B) Speed below normal
C) Constant speed
D) Constant torque
Ans: A

Q720. The braking method used in DC motors includes
A) Regenerative braking
B) Dynamic braking
C) Plugging
D) All of the above
Ans: D

Q721. The direction of induced emf in DC generator is given by
A) Fleming’s right-hand rule
B) Fleming’s left-hand rule
C) Lenz’s law
D) Faraday’s law
Ans: A

Q722. The EMF equation of a DC generator is
A) E = (PΦZN)/(60A)
B) E = (ΦZN)/(P60A)
C) E = (60AΦZ)/N
D) E = (AΦZ)/(60PN)
Ans: A

Q723. In lap winding, the number of parallel paths is equal to
A) 2
B) Number of poles (P)
C) P/2
D) 2P
Ans: B

Q724. In wave winding, the number of parallel paths is always
A) 2
B) 4
C) P
D) P/2
Ans: A

Q725. The induced EMF in a DC generator depends on
A) Flux per pole
B) Speed
C) Number of conductors
D) All of the above
Ans: D

Q726. A DC shunt motor is used where
A) Constant speed is required
B) Variable speed is required
C) High torque is required
D) Speed reversal is needed
Ans: A

Q727. The speed of a DC series motor varies
A) Directly with load
B) Inversely with load
C) Linearly with current
D) Constantly
Ans: B

Q728. A differential compound generator has
A) Series field opposes shunt field
B) Series field aids shunt field
C) No series field
D) Weak shunt field
Ans: A

Q729. In a long shunt compound generator, the shunt field is connected
A) Across armature
B) Across both armature and series field
C) In series with armature
D) Across series field only
Ans: B

Q730. The function of yoke in DC machine is
A) To provide mechanical support
B) To carry magnetic flux
C) To provide protection
D) All of the above
Ans: D

Q731. The efficiency of a DC motor is maximum when
A) Copper losses = constant losses
B) Copper losses = iron losses
C) Input = output
D) Output = losses
Ans: A

Q732. The stray losses in a DC machine include
A) Windage loss
B) Friction loss
C) Brush contact loss
D) All of the above
Ans: D

Q733. The generated emf in DC generator is proportional to
A) Armature current
B) Field current
C) Speed × flux
D) Speed only
Ans: C

Q734. The flux per pole in DC machine depends on
A) Field current
B) Armature current
C) Speed
D) Load
Ans: A

Q735. The magnetic neutral axis (MNA) shifts due to
A) Armature reaction
B) Commutation
C) Speed change
D) Load increase
Ans: A

Q736. A DC series motor is used in
A) Traction
B) Lathes
C) Fans
D) Elevators
Ans: A

Q737. The main advantage of wave winding over lap winding is
A) High current capacity
B) High voltage for same size
C) Simple design
D) Low cost
Ans: B

Q738. The speed of DC motor is directly proportional to
A) Back emf
B) Supply voltage
C) Flux per pole
D) Both A and B
Ans: D

Q739. For same load, the armature current of series motor is
A) Greater than shunt motor
B) Less than shunt motor
C) Same
D) Variable
Ans: A

Q740. The speed control of DC shunt motor by field control is
A) Below normal speed
B) Above normal speed
C) Constant speed
D) None
Ans: B

Q741. The armature reaction in DC machine produces
A) Cross magnetizing effect
B) Demagnetizing effect
C) Both A and B
D) No effect
Ans: C

Q742. The brushes are shifted to new positions due to
A) Armature reaction
B) Poor commutation
C) Voltage drop
D) Temperature rise
Ans: A

Q743. The load on DC generator increases, terminal voltage
A) Increases
B) Decreases
C) Remains same
D) Becomes zero
Ans: B

Q744. The field coils in DC machine are wound on
A) Yoke
B) Pole core
C) Armature
D) Shaft
Ans: B

Q745. The commutator in DC machine is made of
A) Copper segments insulated by mica
B) Aluminum plates
C) Iron discs
D) Steel plates
Ans: A

Q746. The cause of sparking at brushes may be
A) Poor commutation
B) Weak brush spring
C) High load current
D) All of the above
Ans: D

Q747. The magnetic losses in a DC machine are
A) Eddy current and hysteresis losses
B) Copper losses
C) Mechanical losses
D) Brush losses
Ans: A

Q748. The iron losses in DC machines occur in
A) Armature core
B) Yoke
C) Commutator
D) Brushes
Ans: A

Q749. The brushes should be placed at
A) Geometrical neutral axis
B) Magnetic neutral axis
C) Armature axis
D) Axis of poles
Ans: B

Q750. The armature of DC machine rotates because
A) Force acts on current-carrying conductor in magnetic field
B) Magnetic field is stationary
C) Supply voltage is DC
D) Commutator reverses current
Ans: A