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JEE Main 2018 (15 Apr, Shift 2) · Charge Sharing & Loss of Energy

Charge Sharing & Loss of Energy question from JEE Main 2018 (15 Apr, Shift 2)

Q32JEE Main 2018 · 15 APR · SHIFT 2Difficult

Charge Sharing & Loss of Energy

A capacitor C1 = 1.0 μ\muF is charged up to a voltage V = 60 V by connecting it to battery B through switch (1). Now C1 is disconnected from battery and connected to a circuit consisting of two uncharged capacitors C2=3.0 μFC_2=3.0\ \mu\text{F} and C3 = 6.0 μ\muF through switch (2), as shown in the figure. The sum of final charges on C2 and C3 is:

Figure

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Answer: (a)

  1. C2C_2 and C3C_3 in series: C23=3×69=2 μC_{23} = \frac{3 \times 6}{9} = 2\ \muF.
  2. Q=C1V=1×60=60 μQ = C_1V = 1 \times 60 = 60\ \muC is shared between C1C_1 and C23C_{23}: V′=601+2=20V' = \frac{60}{1 + 2} = 20 V.
  3. Charge on the series branch =2×20=40 μ= 2 \times 20 = 40\ \muC (each of C2C_2 and C3C_3 carries this same 40 μ40\ \muC).
  4. So the answer is (a) 40 μ40\ \muC.
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