Revision Notes

4.6.1 Electromagnetic Induction

Inducing an EMF in a Conductor

  • When a conductor (such as a metal wire) is moved through a magnetic field, it cuts through the field lines, inducing an EMF in the wire


em-induction, IGCSE & GCSE Physics revision notes

As the wire moves downwards, it cuts through field lines, inducing an EMF in the wire


  • A similar effect occurs if a magnet is pushed into, or taken out of a coil:
    • As the magnet moved through the coil, the field lines cut through the turns on the coil
    • This induces an emf in the coil

coil-induction, IGCSE & GCSE Physics revision notes

When the magnet enters the coil, the field lines cut through the turns, inducing an EMF


  • More generally, whenever the magnetic field passing through a loop of wire changes, an EMF is induced


Factors Affecting EM Induction

  • The size of the induced EMF is proportional to the rate at which the field lines are cut:
    • If the field lines are cut at a faster rate, the EMF will increase
  • This can be achieved by:
    • Moving the wire (or magnet) faster
    • Using a stronger magnet (increasing the number of field lines)
    • Adding more turns to a coil (assuming a coil is being used, and not just a wire)


Exam Tip

When discussing factors affecting EM Induction:

  • Make sure you state:
    “Add more turns to the coil”
  • And not just:
    “Add more coils”
    (This second one means something slightly different)


  • Likewise, when referring to the magnet, use the phrase:
    “A stronger magnet”
  • And not:
    “A bigger magnet”
    (Large magnets are not necessarily stronger)
Extended Only

The Right-Hand Rule

  • When moving a wire through a magnetic field, the direction of the induced EMF can be worked out by using the Right-Hand Dynamo rule:


Right Hand Dynamo (4), IGCSE & GCSE Physics revision notes

The Right-Hand Dynamo rule can be used to deduce the direction of the induced EMF


  • To use the rule:
    • Start by pointing the first finger (on your right hand) in the direction of the field
      (First Finger Field)
    • Next, rotate your hand so that the thumb point in the direction that the wire is moving in
      (ThuMb Motion)
    • Your Second finger will now be pointing in the direction of the current (or, strictly speaking, the EMF)
      (SeCond Current)
  • The direction of the induced EMF always opposes the change that produces it
  • This means that any magnetic field created by the EMF will act so that it tried to stop the wire or magnet from moving


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Jenna studied at Cardiff University before training to become a science teacher at the University of Bath specialising in Biology (although she loves teaching all three sciences at GCSE level!). Teaching is her passion, and with 10 years experience teaching across a wide range of specifications – from GCSE and A Level Biology in the UK to IGCSE and IB Biology internationally – she knows what is required to pass those Biology exams.

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