The Motor Effect

The motor effect can happen when you put a current-carrying wire in a magnetic field.

A current in a magnetic field experiences a force

When a a current-carrying wire, or any other conductor, is put between magnetic poles, the magnetic field around the wire interacts with the magnetic field it has been placed in. This causes the magnet and the conductor to exert a force on each other. This is called the motor effect and can cause the wire to move.

• To experience the full force, the wire has to be at 90 to the magnetic field. If the wire runs parallel to the magnetic field, it won’t experience any force at all. At angles in between, it’ll feel some force.
• The force always acts at right angles to the magnetic field of the magnets and the direction of the current in the wire
• A good way of showing the direction of the force is to apply a current to a set of rails inside a horseshoe magnet. A bar is placed on the rails, which completes the circuit. This generates a force that rolls the bar along the rails
• The magnitude(strength) of the force increases with the strength of the magnetic field
• The force also increases with the amount of current passing through the conductor

You can find the size of the force…

The force acting on a conductor in a magnetic field depends on three things

• The magnetic flux density-how many field(flux) lines there are in a region. This shows the strength of the magnetic field
• The size of the current through the conductor
• The length of the conductor that’s in the magnetic field

When the current is at 90 to the magnetic field it is in, the force acting on it can be found using the equation:

F=BI1 Force=Magnetic flux density x current x length

And which way it’s acting

You can find the direction of the force with Fleming’s left hand rule

• Using your left hand, point your First finger in the direction of the Field
• Point your seCond finger in the direction of the Current
• Your thuMb will then point in the direction of the force(Motion)
• Fleming’s left hand rule shows that if either the current or the magnetic field is reversed, then the direction of the force will also be reversed. This can be used for all sorts of things-like motors