What will happen if the back e.m.f. of a D.C. motor vanishes suddenly?
The motor will run noisy
The motor will continue to run
The motor will stop
The armature may burn
The armature may burn
Which of the following law/rule can he used to determine the direction of rotation of D.C. motor ?
Lenz’s law
Faraday’s law
Fleming’s left-hand rule
Coloumb’s law
Fleming’s left-hand rule
Starters are used with D.C. motors because
to restrict armature current as there is no back e.m.f. while starting
back e.m.f. of these motors is zero initially
these motors are not self-starting
these motors have high starting torque
to restrict armature current as there is no back e.m.f. while starting
A D.C. series motor is that which
has its field winding consisting of thick wire and less turns
can be started easily without load
has a poor torque
has almost constant speed
has its field winding consisting of thick wire and less turns
In D.C. machines fractional pitch winding is used
to increase the generated e.m.f.
to reduce the sparking
to improve cooling
to reduce copper losses
to reduce the sparking
Three point starter can be used for
both shunt and compound motor
series motor only
shunt motor only
compound motor only
both shunt and compound motor
Sparking is discouraged in a D.C. motor because
none of the above
both and
it increases the input power con-sumption
commutator gets damaged
commutator gets damaged
Speed control by Ward Leonard method gives uniform speed variation
in one direction
below normal speed only
in both directions
above normal speed only.
in both directions
Which of the following motors one will choose to drive the rotary compressor ?
Synchronous motor
Universal motor
D.C. series motor
D.C. shunt motor
Synchronous motor
If the speed of a D.C. shunt motor is increased the back e.m.f. of the motor will
increase
remain same
decrease
become zero
increase
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