How can electricity be used to make things move?

Force on a Current

The diagram below shows a wire in a magnetic field. When the switch is closed a current flows through the wire. We also observe that the wire experiences a force and moves.

You do not need to explain why this happens. What you do need to know is what affects the size and the direction of the force. We can use the left hand rule to work out the direction of the force. Remember that if the current is parallel to the field then there is no force.

Work out the direction of the force, if there is one, in the examples below

The size of the force can be increased by

a)      Increasing the size of the current       b) Increasing the strength of the magnetic field

Motors

We can create movement using electricity. This is what happens in an electric motor. How many electric motors are there in your home? Once you start counting them it is surprising just how many there are.

An electric motor contains a coil in a magnetic field. When a current flows through the coil one side is pushed down and the other is pushed up. This therefore produces a turning effect.

Can you figure out why the direction of the current needs to be reversed every half turn? This is what the commutator in the diagram above does.

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Revision Questions

1.       Write down 10 things in your home that contain electric motors

2.       When will a wire in a magnetic field experience a force?

3.       When wont it?

4.       Check the direction of the forces on the wires in the examples above

5.       How could you make a motor turn faster? Explain your answer.

6.       Other than in a motor, in what other device does a force act on a current carrying coil in a magnetic field?