GCSE Physics Revision — Transformers
Revise Transformers for GCSE Physics with a topic explanation, worked example and common mistakes. Check the board notes for specification differences.
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What is Transformers?
A transformer is a device that changes the potential difference of an alternating current (AC). It consists of two coils of wire, a primary coil and a secondary coil, wrapped around a soft iron core. A step-up transformer increases the potential difference (has more turns on the secondary coil), while a step-down transformer decreases it (has fewer turns on the secondary coil). Transformers only work with AC.
Board notes: A Higher Tier topic for all major GCSE Physics boards (AQA, Edexcel, OCR). The transformer equations are important.
Step-by-step explanationWorked examples
Worked example
A transformer has 200 turns on the primary coil and 2000 turns on the secondary coil. If the input potential difference is 230V, what is the output potential difference? Solution: Use the transformer equation: Vp/Vs = Np/Ns. 230V / Vs = 200 / 2000. Vs = 230V x (2000 / 200) = 2300V. This is a step-up transformer.
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Common mistakes
- 1Thinking that transformers can work with direct current (DC). They rely on a changing magnetic field, which is only produced by AC.
- 2Confusing step-up and step-down transformers. Step-up increases voltage (more secondary turns), step-down decreases voltage (fewer secondary turns).
- 3Assuming that transformers create energy. They are very efficient, but they cannot create energy. If the voltage is stepped up, the current must be stepped down to conserve power (P = VI).
Transformers exam questions
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Frequently asked questions
Why are transformers used in the National Grid?
Step-up transformers are used to increase the voltage for transmitting electricity over long distances. This reduces the current, which in turn reduces energy loss as heat in the cables. Step-down transformers are then used to reduce the voltage to a safe level for use in homes and businesses.
What is the transformer equation?
The ratio of the potential differences across the coils is equal to the ratio of the number of turns on the coils: Vp/Vs = Np/Ns. For an ideal (100% efficient) transformer, the power in equals the power out: VpIp = VsIs.