A Levels Physics (9702)•9702/13/O/N/19

Explanation
Circuit analysis: series-parallel combination yields power in R
Steps:
- Two 6Ω resistors in parallel give equivalent resistance of 3Ω.
- This 3Ω is in series with the third 6Ω resistor R, for total resistance of 9Ω.
- Total current I = 12V / 9Ω = 4/3 A.
- Power in R = I² × 6Ω = (16/9) × 6 = 32/3 W ≈ 11W.
Why C is correct:
- Power formula P = I²R directly gives 32/3 W (≈11W) for the voltage drop across R, per Ohm's law.
Why the others are wrong:
- A: Matches power in each parallel resistor (≈2.7W), not R.
- B: Equals emf divided by R (12V/6Ω=2A, but I=2A gives P=24W, not 6W).
- D: Assumes 12V directly across one 6Ω resistor (P=V²/R=24W), ignoring configuration.
Final answer: C
Topic: Practical circuits
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