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GCSE Physics electricity questions

Use current, charge, potential difference and resistance in series circuits and parallel branches.

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Current in a branch

A 20 Ω resistor and a 40 Ω resistor are in parallel across an ideal 13 V supply. Find current through the 20 Ω branch. Give your answer to 3 significant figures.

Ideal DC supply, wires and meters. Resistors have constant resistance; heating does not change their values.

13 V20 Ω40 Ω
Ideal 13 V supply. 20 Ω and 40 Ω resistors in parallel.
Larger diagram
13 V20 Ω40 Ω

Treat the given values as exact unless an uncertainty is stated.

Use decimals or e notation, e.g. 4.2e-3. Enter the unit separately.

Hint

Each parallel branch has the full supply potential difference. Use that branch’s resistance.

Worked solution
  1. I_1 = 13/20 A.
  2. Answer: 0.650 A (3 significant figures).
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Question type: Mixed practice
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Read a series or parallel circuit before calculating

Two resistors, 4 Ω and 8 Ω, are in series across 6 V. Total resistance is 12 Ω, so current is 0.50 A. Potential differences are 2.0 V and 4.0 V. In parallel across 6 V, each would have 6 V across it and branch currents would be 1.5 A and 0.75 A.

Series components share current; parallel branches share potential difference. Use the voltage and resistance of the same component or branch in V = IR. A minute contains 60 seconds when calculating charge from Q = It.

Analyse current–voltage measurements

Foundation and Higher: this set covers content common to both tiers. Some calculations need several steps.

Current and potential difference

Series resistances add. Each parallel branch has the supply potential difference, and branch currents add to the supply current. Use V = IR for the branch you are asked about. Convert minutes to seconds for Q = It. Electrical energy is QV; power can be found from VI after calculating current. This set excludes reciprocal parallel-resistance calculations and internal resistance.

Work through the practical method and sample results

GCSE scope

AQA 8463: 4.2.1.3–4; 4.2.2; 4.2.4.1–2; OCR Gateway J249: P3.2; PM3.2i–iv. Tasks cover the selected skills listed above.

AQA specification · OCR Gateway specification

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