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JEE Main 2018 (16 Apr, Shift 1) · Capacitors in DC Circuits & RC

Capacitors in DC Circuits & RC question from JEE Main 2018 (16 Apr, Shift 1)

Q37JEE Main 2018 · 16 APR · SHIFT 1Difficult

Capacitors in DC Circuits & RC

In the following circuit, the switch S is closed at t = 0. The charge on the capacitor C1 as a function of time will be given by (Ceq=C1C2C1+C2)\left(C_{eq}=\frac{C_1C_2}{C_1+C_2}\right)

Figure

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Answer: (c)

  1. C1C_1, C2C_2, RR and EE are all in one series loop, so the two capacitors act as one capacitor Ceq=C1C2C1+C2C_{eq} = \frac{C_1C_2}{C_1+C_2}.
  2. Series capacitors carry the same charge, so the charge on C1C_1 equals the charge on CeqC_{eq}.
  3. Charging an uncharged capacitor: q=CeqE(1−e−t/RCeq)q = C_{eq}E\left(1 - e^{-t/RC_{eq}}\right)
  4. So the answer is (c) CeqE[1−exp⁡(−t/RCeq)]C_{eq}E\left[1-\exp\left(-t/RC_{eq}\right)\right].
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