A transformer in an electricity substation changes the potential difference of the electricity supply.
The potential difference across the primary coil is 33 000 V33\ 000\ \text{V}33 000 V.
The current in the primary coil is 40 A.
The potential difference across the secondary coil is 11 000 V11\ 000\ \text{V}11 000 V.
State whether this is a step-up or a step-down transformer. Give a reason for your answer.
Use the equation: potential difference across primary coil×current in primary coil=potential difference across secondary coil×current in secondary coil\text{potential difference across primary coil} \times \text{current in primary coil} = \text{potential difference across secondary coil} \times \text{current in secondary coil}potential difference across primary coil×current in primary coil=potential difference across secondary coil×current in secondary coil
Calculate the current in the secondary coil.
Use the equation: power=potential difference×current\text{power} = \text{potential difference} \times \text{current}power=potential difference×current
Calculate the power transferred to the primary coil.
Give your answer in MW\text{MW}MW.
The cables leaving the secondary coil have the same resistance as the cables going into the primary coil.
Explain why the cables leaving the secondary coil get hotter.
16 exam-style questions on OCR GCSE Physics 8.2 Powering Earth, covering 8.2.1 Renewable and non-renewable energy resources, 8.2.2 Patterns and trends in energy use, 8.2.3 The national grid, 8.2.4 Step-up and step-down transformers, 8.2.5 Efficiency of the national grid, 8.2.6 Transformers and power transmission at high voltage, 8.2.7 The UK domestic supply, 8.2.8 Direct and alternating potential difference, 8.2.9 Live, neutral and earth wires, and 8.2.10 Dangers of mains electricity. Each one has a worked solution and a mark scheme showing where the marks go.