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A2 Daily A Level Physics question

2026-05-11 OCR A Cross-topic problem solving (mechanics <-> circuits energy; graphs & modelling) OCR-A Module 3.3 Work, energy and power OCR-A Module 6.2 Capacitors — energy stored (1/2 C V^2) OCR-A Module 1.1 Practical skills — data analysis and graphs

In a lab, a mass is allowed to fall through height h, turning a small generator that charges a capacitor. For a given setup, students vary h and measure the final capacitor voltage V after the mass comes to rest. Their V^2 vs h plot is a straight line through the origin. Which change would increase the gradient of this V^2–h graph, with all other factors unchanged?

  1. A Use thinner, longer leads so the total circuit resistance is higher.
  2. B Replace the capacitor with one of smaller capacitance. (correct)
  3. C Use a smaller hanging mass while keeping the generator the same.
  4. D Increase mechanical friction in the generator and drive system.

Answer

The correct answer is B.

Correct: B — Replace the capacitor with one of smaller capacitance. For the same mechanical energy per unit height, a smaller C requires a larger V^2 to store that energy, so the V^2–h gradient increases. A increases resistive losses so less of mgh reaches the capacitor, reducing the gradient. B is correct because decreasing C raises V^2 for a given transferred energy, steepening the line. C reduces the available gravitational energy per metre (smaller m), so the gradient decreases. D adds mechanical losses (lower efficiency), so less energy reaches the capacitor and the gradient falls.

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