AS Daily A Level Physics question
A camper uses a 12 V battery to run two identical 6 Ω heating pads. They try wiring the pads (i) in series and (ii) in parallel across the same battery. Comparing the total electrical power drawn from the battery, which statement must be true?
Answer
The correct answer is A.
Correct: A — Parallel draws four times as much power as series. A is correct because at fixed supply voltage total power is inversely proportional to total resistance: series R = 6 + 6 = 12 Ω gives P = 144/12 = 12 W, while parallel R = (6||6) = 3 Ω gives P = 144/3 = 48 W, so 48 is four times 12. B is wrong because it underestimates the effect: the resistance falls from 12 Ω (series) to 3 Ω (parallel), a quarter, so power increases fourfold, not twofold. C is wrong because the total resistances differ (12 Ω vs 3 Ω), so with the same 12 V they cannot draw the same power. D is wrong because higher total resistance in series reduces power rather than increasing it.