AS Daily A Level Physics question
A camping setup uses a 12 V battery and two identical resistive heating pads each rated "6.0 W at 12 V". When correctly wired in parallel, both run from 12 V. A student mistakenly wires the two pads in series across the same 12 V battery. Treat each pad as having constant resistance equal to its rated operating resistance. Compared with the correct parallel wiring, how does the total electrical power delivered to the two pads change?
Answer
The correct answer is C.
Correct: C — It quarters to about 3 W. Each pad has R = 12^2 / 6.0 = 24 Ω; in parallel total power is 2 × 6.0 = 12 W, while in series R_total = 48 Ω so power is 12^2 / 48 ≈ 3 W, a quarter. A This suggests only a small change, but series wiring makes the total resistance four times that of the parallel equivalent (48 Ω vs 12 Ω), so the power drop is much larger than a slight decrease. B Power does not halve: going from 12 Ω (parallel) to 48 Ω (series) means power at fixed 12 V is one quarter (P ∝ 1/R), not one half. C Matches the calculation: 3 W total is one quarter of the 12 W in the correct parallel case. D Series increases total resistance, so current and power both decrease; an increase to 18 W is not possible.