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AS 91526 · 2023 paper · capacitors

Question 1(c) Achieved

Practises Capacitors

Kate investigates a capacitor found in a camera, labelled 185 nF (1.85 × 10⁻⁷ F). The camera also contains a 1.50 V “AA” battery.

C185 nF
V1.50 V

The rolled-up plates act like two metal rectangles 3.2 × 10⁻² m × 1.83 m, with a dielectric of relative permittivity 2.10 between them.

Calculate the distance between the metal rectangles.

The 2023 paper, page 3 ↗ Marking schedule, page 2 ↗

Work it out

Try it on paper first. Stuck? Take one hint at a time.

  1. 1 Which formula links a parallel-plate capacitor’s shape to its capacitance?

    C = ε0εrA / d, where ε0 = 8.85 × 10−12 F m−1 is the permittivity of free space and εr the dielectric’s relative permittivity.

  2. 2 What is the area of one plate?

    A = 3.2 × 10−2 × 1.83 = 0.05856 m².

  3. 3 Rearrange for d and substitute, with C = 185 nF in farads.

    d = ε0εrA / C = (8.85 × 10−12 × 2.10 × 0.05856) / (1.85 × 10−7) = 5.88 × 10−6 m.
Answer 5.88 × 10−6 m (about 6 µm)

What the marker wanted

  • Achieved The separation, 5.88 × 10−6 m.

In our words, from NZQA’s 2023 marking schedule.

How did it go?

Got it moves it further out. Review brings it back tomorrow.