WAEC Physics 2021 Theory — Question 26
Question 26 of 35 from the West African Examinations Council (WAEC) Physics 2021 Theory paper, with the correct answer and a full explanation.
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11(c)(ii). Obtain the equivalent capacitance, in terms of C₂, of the two capacitors (with plate separations 2 mm and 5 mm) shown connected in the diagram.
Model answer
Since capacitance C∝1/d (plate separation) for otherwise identical capacitors, C1/C2 = d2/d1 = 5/2, so C1=(5/2)C2. For capacitors in series: CT = C1C2/(C1+C2) = [(5/2)C2×C2] / [(5/2)C2+C2] = (5/2 C2²)/(7/2 C2) = (5/7)C2.
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