A current carrying wire experiences a force when the wire is in a magnetic field.

Movement from Magnetism

The direction of the force can be changed by:

1. changing the direction of the magnetic field (swapping

over the north & south poles).

2. changing the direction of the current (swap the “+” and

“-” connections at voltage supply).

N S

current

Force

The Electric Motor

A

BC

D

N S

field magnets

rotating coilbrushes

commutator

How it Works…

1. An electric current flows through the wires wound around the

rotating coil.

2. The magnetic field caused by the current in the wire and the

magnetic field produced by the field magnets combine and

force one side (AB) of the rotating coil up, and the other side

(CD) down.

3. When the coil is in the upright position, the commutator causes

the direction of the electric current to be reversed.

4. This means that AB, which was being pushed up, is now pulled

down.

5. The process continually repeats allowing the motor to

continually rotate.

What the parts do…

Brushes pushed lightly against commutator allowing current to flow from the supply to

rotating coil.

Commutator free to rotate about a central axis and is responsible for reversing current when motor reaches upright positions.

Rotating Coil magnetic field produced when current flows.

Field Magnets produce permanent magnetic field.

Rotating coil moves in

anti-clockwise direction.

Current direction changed.

Rotating coil now moves in

clockwise direction.

Magnetic field direction changed.

Rotating coil moves in

clockwise direction.

SouthNorth

Battery

- +

NorthSouth

Battery

+ -

SouthNorth

Battery

+ -

Commercial Motors

carbon brushes

carbon brushes

field coil

field magnet

axle (shaft)

commutator

Real motors have some differences from our simple model of an electric motor.

• Carbon brushes are used as they are:

good conductors.

soft and won’t damage the commutator.

cheap to replace when they wear down too much.

• Electromagnets are used to provide the magnetic field as they are lighter and cheaper than permanent magnets.

• There are many rotating coils, each requiring TWO parts on a multi-section commutator. This allows the motor to spin more smoothly.