Explaining how a transformer works
Teaching Guidance for 14-16
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
carriedby 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.