DC Motor Questions

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.

Tags

NGSS.HS-PS2-5

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

Tags

NGSS.HS-PS3-5

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

Answer explanation

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