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Electricity

Circuits

  • 6 things to know
  • Papers 1 and 3

Overview

Resistors in series and parallel, the circuit rules, and the equations for electrical power.

What you need to know

Answer each one before you reveal it.

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Numbers

How is total resistance found in series, and how is electrical power calculated?

Numbers

When would you use P = I²R rather than P = V²/R, and what is true of current in series?

Numbers

Why is current the same everywhere in series, and how do the potential differences add?

Numbers

What happens to emf and current capability when identical cells are connected in parallel?

Numbers

Explain why the sum of potential differences around a closed loop must equal the total emf

Key term

Explain why an ammeter is connected in series rather than in parallel

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    State the formula for calculating total resistance when resistors are connected in series.

    Model answer

    Rₜ = R₁ + R₂ + R₃ + ...

  2. 2

    Explain why the total resistance of resistors in series is always greater than any individual resistance.

    Model answer

    Each resistor adds its own opposition to current flow, so the total opposition (resistance) accumulates as current must pass through all resistors sequentially.

  3. 3

    Explain why the total resistance of resistors in parallel is always less than the smallest individual resistance.

    Model answer

    Parallel resistors provide multiple pathways for current, reducing the overall opposition to current flow compared to any single pathway alone.

  4. 4

    State the equation used to calculate electrical energy transferred in a circuit.

    Model answer

    E = IVt

  5. 5

    Define each term in the equation E = IVt.

    Model answer

    E is electrical energy transferred (in joules), I is current (in amperes), V is potential difference (in volts), and t is time (in seconds).

  6. 6

    Calculate the energy when current = 1.8 A, potential difference = 6 V, time = 116 s.

    Model answer

    Energy = 1.8 × 6 × 116 = 1250 J.

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