Electric Circuits Problem Solving

This final lesson brings together everything you have learned about electric circuits. The key to success in A-Level circuit questions is a systematic approach: identify the circuit structure, choose the right equations, and work through the calculation step by step.

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Strategy for Multi-Step Circuit Problems

When faced with a complex circuit problem, follow this approach:

1. Draw or annotate the circuit diagram. Label all known values (EMF, resistances, currents, voltages).
2. Identify series and parallel sections. Simplify parallel combinations into single equivalent resistances.
3. Find the total resistance of the entire circuit (including internal resistance if given).
4. Calculate the total current from the supply using I = ε/(R_total + r) or I = V/R.
5. Work outwards to find voltages and currents in individual components.
6. Check your answer — do the voltages add up? Do the currents at junctions balance?

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Worked Example 1: Combined Series-Parallel Circuit