WorksheetsELECTRIC MACHINES
Total questions: 24
Worksheet time: 12mins
WHICH OF THE FOLLOWING IS THE FORCE-PRODUCING DEVICE?
MOTORS
RELAYS
GENERATORS
PICK-UPS
ROTORS AND STATORS ARE MADE UP OF _________MATERIALS.
DIMAGNETIC
CAST IRON
MILD STEEL
FERROMAGNETIC
WHAT IS THE USE OF COMMUTATOR IN A DC GENERATOR?
TO CONVERT GENERATED EMF INTO ALTERNATING VOLTAGE
TO CONVERT THE GENERATED ALTERNATIVE EMF INTO DIRECT VOLTAGE
TO CONVERT ELECTRICAL ENERGY INTO MECHANICAL ENERGY
TO CONVERT MECHANICAL ENERGY INTO ELECTRICAL ENERGY
If a straight conductor is placed in the magnetic field produced by a permanent magnet, the direction of the current flowing through a conductor is
ANTI-CLOCKWISE
PARALLEL TO THE STRAIGHT CONDUCTOR
CLOCKWISE
PERPENDICULAR TO THE STRAIGHT CONDUCTOR
No-load speed of which of the following motors will be highest?
SHUNT MOTOR
CUMUILATIVE COMPOUND MOTOR
SERIES MOTOR
DIFFERENTIATE COMPOUND MOTOR
Which one of the following is the commonly used method in controlling elevators and rolling mills?
RHEOSTATIC
REGENERATIVE
MAGNETIC
PLUGGING
IN WHICH OF THE FOLLOWING CASES DYNAMIC BRAKING CANNOT BE USED?
FOR LOW CURRENT APPLICATIONS
FOR LONG HEAVY LOADS
FOR HIGH CURRENT APPLICATIONDS
FOR HIGH VOLTAGE APPLICATIONS
ELECTRICAL BRAKING OF ANY VARIETY BECOMES LESS EFFECTIVE AS-
SPEED INCREASES
INDEPENDENT OF SPEED
DEPENDS OF SUPPLY VOLTAGE
SPEED DECREASES
PLUGGING PROVIDES ________ TORQUE BRAKING
SMALLEST
HIGHEST
MEDIUM
ZERO
FOR WHICH MOTOR DYNAMIC BREAKING IS VERY EFFECTIVE?
SHUNT MOTOR
SERIES MOTOR
SEPARATELY EXCITED MOTOR
DIFFERENTIAL COMPOUND MOTOR
Shunt motor is a
variable speed motor
heavy load motor
low torque motor
constant speed motor
In regenerative breaking the regeneration occurs when
EB>V
V>EB
EB>IA
IA>V
Torque is equal to
Speed x Current
current x force
force x perpendicular distance
applied voltage x speed
Why is a starter required in a motor?
to control speed
to control starting torque
to maintain back emf
to control starting current
In a dc shunt motor the torque is proportional to
Flux
Speed
Applied Voltage
Armature Current
To start a DC shunt motor the type of starter is
1 point
3 point
2 point
4 point
A three point starter is used to
minimize back emf
minimize armature current
maximize armature current
maximize back emf
What is the purpose of the external resistance at the time of starting a DC motor
increase starting torque
increase armature flux
reduce the starting current
maintain the constant flux
The F or Z terminal of the starter is connected to.
armature
dc source
neutral
field winding
Speed of DC shunt motor is
Directly proportional to the square of armature current
Inversely proportional to the armature current
Independent of armature current
Directly proportional to armature current
Which of the following is the best breaking method?
Friction
Eddy Current
Electromechanical action
Electrical Breaking
If a DC motor is connected across the AC supply it will
run at normal speed
run at a lower speed
not run
burn due to heat produced
During Rheostatic braking of DC series motor,
motor is run as generator
motor is reversed in direction
motor is run at reduced speed
motor do not run
If the speed of a DC shunt motor is increased , the back emf of the motor will
increase
becomes zero
remains same
decrease
