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A2 Daily A Level Physics question

2026-05-08 OCR A Energy and power in DC circuits (Module 4) OCR A Physics A (H556) Module 4.2.1 Charge and current OCR A Physics A (H556) Module 4.2.2 Energy, power and resistance OCR A Physics A (H556) Module 4.2.3 Electrical circuits (I–V basics)

In a lab test, a metal-film resistor behaves ohmically with resistance 6.0 Ω. The technician increases the DC supply from 3.0 V to 6.0 V. Which statement about the power dissipated in the resistor is correct?

  1. A It doubles, because current doubles when the voltage is doubled across a fixed resistor.
  2. B It stays the same, because the resistor value does not change.
  3. C It becomes four times as large, because both voltage and current double. (correct)
  4. D It halves, because doubling the voltage makes the resistance half as big.

Answer

The correct answer is C.

Correct: C — It becomes four times as large, because both voltage and current double. For an ohmic resistor, doubling V doubles I, so power (V×I) becomes 2×2 = 4 times bigger; numerically, at 3.0 V: I = 0.50 A and P = 1.5 W, at 6.0 V: I = 1.0 A and P = 6.0 W (four times). A is wrong because it ignores that power depends on both voltage and current, not just the current doubling. B is wrong because even though resistance is unchanged, changing the voltage and current changes the power. C is the only statement consistent with the proportional changes in V and I for an ohmic resistor. D is wrong because the resistance of an ohmic resistor does not halve when the applied voltage doubles; resistance is constant in this model.

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