ELECTRICAL MACHINE 1 (DC MACHINE & MOTOR)

by looking at which part of the motor, it can be easily confirmed that a particular motor is DC motor?

• Frame

• Commutator

• Shaft

• Stator

if a speed of a DC shunt motor is increased, the back emf of the motor will

• increase

• remain same

• decrease

• become zero

as the load is increased the speed of DC shunt motor will

• reduce slightly

• increase slightly

• increase proportionately

• remain unchanged

it is a DC motor that tends to over-speed when the field opened while running.

• shunt motor

• series motor

• split phase motor

• over-compounded motor

A DC shunt motor is rotating in clockwise directions as viewed from one end. The polarity of connection of the armature and field winding are reversed simultaneously. The motor will

• rotate in clockwise direction

• rotate in anti-clockwise direction

• will not rotate at all

• gain excessively high speed

DC shunt motors are ed for driving

• trains

• hoists

• cranes

• machine tools

which DC motor will be preferred for elevators?

• shunt motor

• series motor

• differential compound motor

• cumulative compound motor

which of the following statement is correct. in case of a DC series motor?

• it should be directly connected to the load

• it may run away if its field becomes open

• it is a constant speed motor

• it cannot be used where high starting torque is required.

for both lap and wave windings, there are as many commutator bars as the number of

• poles

• slots

• armature conductors

• winding elements

for a DC generator when the number of poles and the number of armature conductors is fixed, then which winding will give the higher emf?

• lap winding

• depends on other features of design

• wave winding

• either of (A) and (C) above