## February 13, 2012

### 6.15 Electromagnetic induction

Recall that a voltage is induced in a conductor or a coil when it moves through a magnetic field or when a magnetic field changes through it; also recall the factors which affect the size of the induced voltage

We know that if there’s a magnetic field perpendicular to a current in a wire, the wire moves perpendicular the field and the current.
But what happens if we move a wire in a magnetic field…? We get a current induced in the wire

We can show this by moving wire connected to an ammeter through a magnetic field. Move the wire in one direction we get a positive reading; and in the other, a negative. But when there is no movement there is no current
We can use this to identify that:
• Using a magnetic field and movement we can create a current
• Using a current and a magnetic field we create movement
• \ We can see that any combination of a current, magnetic field and motion create the other one.

Model question:
Explain carefully how you can induce a current in a wire [3]
• The wire must be perpendicular to the magnet
• The wire and magnetic field must move relative to each other
• The wire must cut through the magnetic field lines as it moves
• The induced current perpendicular to both the field lines and the motion