Question
What is the purpose of the commutator in a d.c. electric motor?
A to control the speed at which the motor rotates
B to reverse the direction of the voltage across the power supply every half-turn
C to reverse the direction of the current in the motor coil every half-turn
D to reverse the direction of spin of the motor coil every half-turn
Answer/Explanation
Ans: C
Question
A simple d.c. electric motor is fitted with a coil that rotates in a magnetic field. A commutator
connects the power supply to the coil.
What is the purpose of the commutator?
A. It converts a.c. into d.c. in the coil.
B. It prevents the current from becoming too great, because the coil has a low resistance.
C. It reverses the direction of the current in the coil after every 180° rotation of the coil.
D. It switches the current off momentarily after every 90° rotation of the coil.
Answer/Explanation
Ans: C
Question
The diagram shows a simple d.c. electric motor which is rotating.
Which change will make the motor rotate more quickly?
A. increasing the number of turns on the coil
B. removing the magnets
C. reversing the battery
D. reversing the polarity of the magnets
Answer/Explanation
Ans: A