Electromagnetic Effects

• Electromagnetic Induction: If a wire is passed across a magnetic field/changing magnetic field, a small EMF is induced and can be detected by a galvanometer.

• The direction of an induced EMF opposes the change causing it.

• The induced EMF can be increased by:

  • moving the wire faster

  • using a stronger magnet

  • Increasing length of wire in magnetic field, e.g. looping the wire through the field several times.

• The current and EMF direction can be reversed by:

  • moving the wire in the opposite direction

  • turning the magnet round so that the field direction is reversed

• Fleming's right-hand rule gives the current direction:

Bar magnet pushed into coil

• The induced EMF (and current) can be increased by:

  • moving the magnet faster

  • using a stronger magnet

  • increasing the number of turns in the coil

• If the magnet is pulled away, the direction of the induced EMF (and current) is reversed

• Using South pole instead of North pole reverses direction of induced EMF (and current)

• If the magnet is held still, there is no EMF

• An induced current always flows in a direction such that it opposes the change which produced it.

• When a magnet is moved towards a coil the pole of the coil and magnet next to each other are the same.

• When the magnet is moved away the poles are opposite (opposite poles attract).

• The pole-type (north or south) is controlled by the direction in which the current is induced.

• The direction of the current is given by the right-hand grip rule:

• The fingers point in the conventional current direction and the thumb gives the North Pole.