A three pole electric DC motor



A DC motor generates a rotating force via attraction and repulsion of magnetic fields. The magnetic fields in a three pole DC motor are generated by three electromagnets and two permanent magnets, as shown on the right. A section of the motor, called the commutator, connects the brushes to the coils and allows for current to flow from the power source, through the coils and back to the power source. It has another very important function and that is, it reverses the flow of current through the coils and so allows for a constant torque to be generated in one direction.

Notice how the poles of the electromagnets change as the commutator rotates around the brushes.



This reversal of current flow allows for the generation of magnetic forces of attraction and repulsion which rotates the rotor in one direction with some force. This force is known as torque.


1) What is the direction of motion of the armature shown on the right?

2) What type of force acts on:
- A
- B
- C

3) The current travels through the coils of wire from

4) What is the function of the commutator?

5) What is the armature?


6) Consider the diagram on the right of two CD motors powered by the same battery. Which one will deliver the greatest torque? Explain why