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WorksheetsDC Motor Questions
Total questions: 15
Worksheet time: 15mins
Why does a DC motor need to be turned on using a starter?
To protect the motor from damage caused by high starting currents.
To prevent the risk of electrocution from high starting currents.
To prevent the risk of electrocution from high starting voltages.
To increase the input voltage to a high enough level to turn on the motor.
Why is there a high current when a DC motor is first turned on?
The resistance is very low on startup.
When the motor is turned on there is no back EMF.
When the motor is turned on the back EMF is very small.
The resistance is zero on startup.
How does the DC starter reduce the current on startup?
There is a large resistance permanently in the circuit.
There is resistance in the circuit that can be decreased in stages.
There is an inductor in the circuit.
There is a capacitor in the circuit.
How does the overload release protect the motor from power surges?
Its magnetism increases and it attracts a lever which causes a short circuit and demagnetises the no volt coil.
Its magnetism increases and it attracts a lever which causes a short circuit and magnetises the no volt coil.
Its magnetism decreases and it attracts a lever which causes a short circuit and magnetises the no volt coil.
Its magnetism decreases and it attracts a lever which causes a short circuit and demagnetises the no volt coil.
The speed of a DC series wound motor can be varied by..
a variable resistor placed in series with the armature
a variable resistor placed in series with the field coil
a variable resistor placed in parallel with the armature
a variable resistor placed in parallel with the field coil
The speed of a DC shunt wound motor can be varied by..
a variable resistor placed in series with the armature
a variable resistor placed in series with the field coil
a variable resistor placed in parallel with the armature
a variable resistor placed in parallel with the field coil
As the current in the armature increases the motor speed
increases
decreases
stays the same
is zero
The no-load speed of a compound motor is 1,650 rpm. How fast will it operate when it delivers rated horsepower output, if the speed regulation is 12.5 percent?
1,444 rpm
1,467 rpm
1,856 rpm
1,500 rpm
What is the primary function of a commutator in a DC motor?
To reverse the direction of current in the armature windings
To increase the voltage output
To decrease the resistance in the circuit
To maintain a constant speed
Which component of a DC motor is responsible for producing the magnetic field?
Armature
Commutator
Field windings
Brushes
What happens to the speed of a DC motor if the load on the motor is increased?
The speed increases
The speed decreases
The speed remains constant
The speed becomes zero
In a DC motor, what is the effect of increasing the armature current on the torque produced?
Torque increases
Torque decreases
Torque remains constant
Torque becomes zero
Why are brushes used in a DC motor?
To provide electrical contact between the stationary and rotating parts
To clean the commutator
To cool the motor
To increase the speed of the motor
What is the role of back EMF in a DC motor?
To oppose the applied voltage and regulate the speed
To increase the current flow
To decrease the resistance
To enhance the magnetic field
How can the direction of rotation of a DC motor be reversed?
By reversing the polarity of the supply voltage
By increasing the load
By decreasing the armature resistance
By increasing the field current
