# Transformers

I can describe how a transformer works and solve problems using transformer equations.

# Transformers

I can describe how a transformer works and solve problems using transformer equations.

## Lesson details

### Key learning points

- A potential difference that causes a current to flow in the primary coil magnetises the iron core.
- When the iron core is magnetised, it induces a potential difference across the secondary coil.
- An AC gives the changing magnetic field needed to induce a potential difference across the secondary coil.
- Transformers are almost 100% efficient so the power output is equal to the power input.
- The ratio of the number of turns on the coils is equal to the ratio of the potential differences across them.

### Common misconception

The size of the current in the primary coil controls the size of current in the secondary coil.

Explain how the p.d. across and resistance of the secondary circuit determines the secondary p.d. and therefore current, and how the current adjusts to ensure that the power input is equal to the power output.

### Keywords

Primary coil - a coil of insulated wire in a transformer, across which potential difference is applied

Secondary coil - a coil of insulated wire in a transformer, across which potential difference is induced

Soft iron core - pure iron inside the coil of an electromagnet that loses all of its magnetism when the electromagnet turns off

Induced p.d. - the p.d. across a conductor caused by a magnetic field moving relative to it

Efficiency - the proportion or percentage of energy supplied to a device that is transferred in a useful way

### Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

## Video

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## Starter quiz

### 6 Questions

describes the coil across which p.d. is applied

describes a transformer that increases the p.d.

describes a transformer that decreases the p.d.

describes the coil across which p.d. is induced

25 kV

33 kV, 11 kV or 450 V

230 V

400 kV