Topic Summaries

Transformers (HT ONLY)

GCSE > Physics > CCEA > GCSE Physics Topic Summaries > Motor effect, generator effect, and transformers > Transformers (HT ONLY)
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Charge, current, and electric fields

Stopping, braking, and momentum

Science skills: Measuring results

  • A transformer consists of two coils wrapped around an iron core. When an alternating current flows through one coil, it induces a magnetic field around it.
    • This magnetic field is periodically changing direction and is concentrated by the iron core, so it induces an alternating current in the other coil.
    • An iron core is used as it is easily magnetised.
  • Transformers are used to change an alternating potential difference.
    • Step-up transformers increase potential difference by having more turns on their secondary coils.
    • Step-down transformers decrease potential difference by having more turns on their primary coils.
  • The transformer equation states that the ratio of potential differences and turns in the coils of a transformer are equal: \(\dfrac{V_p}{V_s}=\dfrac{n_p}{n_s}\) where \(V_p\) and \(V_s\) are the potential differences in the primary and secondary coils respectively in V, and \(n_p\) and \(n_s\) are the number of turns in the primary and secondary coils respectively.
  • If a transformer is 100% efficient, then there are no energy losses and the input power to the primary coil is equal to the output power from the secondary coil. This can be written as \(V_s\times I_s = V_p\times I_p\).

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