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WorksheetsDEPTALS LAST YR CONCEPT
Total questions: 15
Worksheet time: 8mins
Which of the following statements is FALSE for a series-wound DC motor?
The speed decreases with increase of resistance in the armature circuit
The speed increases as the flux decreases
The speed can be controlled by a diverter
The speed can be controlled by a shunt field regulator
Which of the following statements is FALSE?
A series-wound motor has a large starting torque
The speed of a series-wound motor drops considerably when load is applied
A shunt wound motor must be permanently connected to its load
A shunt wound motor is essentially a constant speed machine
The speed of a DC motor may be increased by
Increasing the armature current
Decreasing the field current
Decreasing the applied voltage
Increasing the field current
The effect of inserting a resistance in series with the field winding of a shunt motor is to
Increase the magnetic field
Increase the speed of the motor
Decrease the armature current
Reduce the speed of the motor
With a DC motor, the starter resistor
Limits the armature current to a safe starting value
Limits the field current to a safe starting value
Prevents the field current flowing through and damaging the armature
Controls the speed of the machine
The rotating part of a DC motor is known as
Pole
Carbon brush
Stator
Armature
The counter e.m.f. of a DC motor is zero when the
Armature is not turning
Motor is at rated speed
Armature just begins to turn
Motor is almost up to rated speed
The speed of the DC motor is directly proportional to its
Armature current
Back e.m.f.
Flux per pole
Torque
Which of the following statements is FALSE?
A DC motor converts electrical energy to mechanical energy
The efficiency of the DC motor is the ratio input power to output power
A DC generator converts mechanical power to electrical power
The efficiency of the DC generator is the ratio output power to input power
Which of the following statements is FALSE?
A commutator is necessary in a DC motor to keep the armature rotating in the same direction
A commutator is necessary in a DC generator to produce unidirectional voltage at the terminals
The field winding of a DC machine is housed in slots on the armature
The brushes of DC machines are usually made of carbon and do not rotate with the armature
The direction of rotation of a DC shunt motor can be reversed by interchanging
The supply terminals
The armature terminals only
The field terminals
Either field or armature terminals
The mechanical power developed by the armature of a DC motor is equal to
Armature current multiplied by back e.m.f.
Power output multiplied by efficiency
Power input minus losses
Power output plus iron losses
The induced e.m.f. in the armature conductors of a DC motor is
Sinusoidal
DC pulsating
Depends on the type of DC machine
Direct current
In Fleming’s right-hand rule, the thumb represents the
Direction of the conductor’s motion
Direction of the induced current
Direction of the magnetic field
Direction of induced e.m.f.
Generation of voltage in a generator can only happen when
There is a rotary conductor
There is relative motion between conducting wires and magnetic line of force
There is a magnetic field in a conductor
There is a relative motion between conductor and electric field
