Physics (AS & A Level) · Oct / Nov 2016 · Paper 42 · Question 7
9702
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7(a)(i)[1]
charge / potential (difference) or charge per (unit) potential (difference) [1]
7(a)(ii)[2]
(V = Q / 4πε0r and C = Q / V) for sphere, C (= Q / V) = 4πε0r C = 4π × 8.85 × 10–12 × 12.5 × 10–2 = 1.4 × 10–11 F [2]
7(b)(i)[1]
1 / CT = 1 / 3.0 + 1 / 6.0 CT = 2.0 µF [1]
7(b)(ii)[2]
total charge = charge on 3.0 µF capacitor = 2.0 (µ) × 9.0 = 18 (µC) potential difference = Q / C = 18 (µ)C / 3.0 (µ)F = 6.0 V [2]
or argument based on equal charges: 3.0 × V = 6.0 × (9.0 – V) (C1) V = 6.0 V (A1)
7(b)(iii)[2]
potential difference (= 9.0 – 6.0) = 3.0 V charge (= 3.0 × 2.0 (µ)) = 6.0 µC [2]
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