Explaining how a transformer works(Challenge)



An explanation of several interlinked steps–so take particular care

Wrong Track: The electric current flows around the primary coil… it then goes through the iron core and into the secondary coil.

Right Lines: There is no direct electrical link between the primary and secondary coil. The transformer core does not carry an electric current; it carries a changing magnetic field.

Building up an explanation, step by step

Thinking about the teaching

The explanation for the working of a transformer is a multi–step story that most students will find pretty demanding.

What are the key steps in explaining how a simple transformer works? Let's think about a simple transformer set-up with input and output coils and a changing (alternating) potential difference across the primary.

  • The changing potential difference drives a changing electric current round the primary.
  • The changing electric current in the input produces a changing magnetic field: when the current is zero, the field is zero; when the current is at a maximum, the magnetic field is at maximum strength.
  • The changing magnetic field is carried by the transformer core and linked to the output coil.
  • The changing magnetic field linking the output induces a changing potential difference across the secondary coil.
  • The changing potential difference across the secondary coil drives a changing current through that coil.
  • Two points to bear in mind with this explanation are:

  • There is no electrical connection between input and output coils: the linkage is through the changing magnetic field.
  • Even though the explanation involves going through a sequence of five steps, the steps occur simultaneously in real time.


  • Prepare for teaching across the topic using these links

    topic kitset topic path core ideas (topic) decisions to make (topic) suggestions (for the topic) topic issues



    This is a nugget in the TL thread – connect all three threads from any link

    Physics Narrative (PN) Teaching & Learning Issues(TL) Teaching Approaches(TA)

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