AS Daily A Level Physics question
In a lab test, a fixed 12 Ω resistor is connected to a variable d.c. supply. The potential difference across it is increased from 3.0 V to 6.0 V. Which statement must be true about the power it dissipates?
Answer
The correct answer is B.
Correct: B — It quadruples. For a fixed resistor, doubling the potential difference also doubles the current, so power (product of p.d. and current) scales as 2 × 2 = 4; equivalently, P ∝ V² for constant resistance, so (6/3)² = 4. A It doubles — wrong because this assumes the current stays the same; in a fixed resistor the current also doubles, so the increase is more than ×2. B It quadruples — correct because both voltage and current double, giving four times the power. C It halves — wrong because increasing the p.d. cannot reduce the power in a fixed resistor. D It stays the same — wrong because higher voltage and higher current mean greater power dissipation.