Electromagnetic Induction (CIE IGCSE Physics: Co-ordinated Sciences (Double Award))

Extended tier only

• An electromotive force (e.m.f.) is induced in a conductor whenever there is relative movement between the conductor and a magnetic field
• This could be when
  • the conductor moves in a stationary magnetic field
  • the conductor is stationary in a changing magnetic field

Induced e.m.f. due to a moving conductor

• For an electrical conductor moving in a fixed magnetic field:
  • the conductor (e.g. a wire) cuts the field lines
  • an e.m.f. is induced in the wire

When an electrical conductor moves in a magnetic field an e.m.f. is induced

Induced e.m.f. due to a moving field

• For a fixed conductor in a changing magnetic field:
  
  • as the magnet moved through the conductor (e.g. a coil), the field lines cut through the turns on the conductor (each individual wire)
  • an e.m.f. is induced in the coil

When a magnet is moved towards a wire, the changing magnetic field induces a current in the coil of wire

• A sensitive voltmeter can be used to measure the size of the induced e.m.f.
• If the conductor is part of a complete circuit then a current is induced in the conductor
  • This can be detected by an ammeter

Extended tier only

Factors affecting the magnitude of the induced e.m.f.

1. The speed at which the wire, coil or magnet is moved:

• • Increasing the speed will increase the rate at which the magnetic field lines are cut
  • This will increase the size of the induced e.m.f.

2. The number of turns on the coils in the wire:

• • Increasing the number of turns on the coils in the wire will increase the size of the induced emf
  • This is because each turn (loop) of wire in the coil cuts the magnetic field lines 
  • Therefore, the total induced e.m.f. increases with each additional turn (loop)

3. The size of the coils:

• • Increasing the area of the coils will increase the size of the induced e.m.f.
  • This is because there will be more wire to cut through the magnetic field lines

4. The strength of the magnetic field:

• • Increasing the strength of the magnetic field will increase the size of the induced e.m.f.
  • This is because there will be more magnetic field lines in a given area

Factors affecting the direction of the induced e.m.f.

1. The orientation of the poles of the magnet:

• • Switching the poles of the magnet induces an e.m.f. in the opposite direction

2. The direction in which the wire, coil or magnet is moved:

• • Reversing the direction in which the wire, coil or magnet is moved induces an e.m.f. in the opposite direction