Multiple choice

In a network of four capacitors where three are connected in series of 5 μF to a 240 V supply, which of the following charges on the fourth capacitor of 5 μF is connected in parallel with the three capacitors?

  1. 12 x 10-4 C

  2. 400 x 10-6 C

  3. 0.020 x 10-6 C

  4. 48 x 106 C

  5. 0.0069 x 10-6 C
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A Correct answer
Explanation

Three capacitors are connected in series, hence their equivalent capacity will be: Cs = C / 3 = 5 / 3. This equivalent series capacity is then connected in parallel with the fourth capacitor, hence the final equivalent capacity will be: Cs + C 4 = 5 / 3 + 5 = 20 / 3 = 6.66 6 μF. Now, charge on C1, C2 and C3 is same as they are in series. It is given by: Q = Cs V = 5 / 3 x 240 = 5 x 80 x 10 - 6 C = 4 x 10-4 C Charge on C4= C4 x V = 5 x 240 = 1200 x 10-6 = 12 x 10-4C.

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