The motor effect

A simple electric motor can be built using a coil of wire that is free to rotatebetween two opposite magnetic poles. When an electric current flows through the coil, the coil experiences a force and moves. This is called the motor effect.

This size of the force is greatest when the wire is perpendicular to the magnetic field of the permanent magnet. In other words, it cuts through the magnetic field at 90°. If the wire is parallel to the magnetic field, it will not experience any force.

Working out the direction of the force

The direction of the force - and therefore the movement of the wire - can be determined using Fleming’s left hand rule.

To do this, spread out your left thumb, forefinger (index finger) and second finger so they are all at 90° to one another:

• • point your forefinger (index finger) in the direction of the magnetic field (north to south)

  • point your second finger in the direction of the electric current (positive to negative)

Your thumb will point in the direction of movement.

Remember:

• • thuMB – Movement

  • Forefinger – magnetic Field

  • seCond finger – Current

Note that the direction of the force is reversed if either the direction of the current is reversed, or if the direction of the magnetic field is reversed.

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