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The effective capacitance of the parallel combination of two capacitors C₁ and C₂ is 10 μ F. When these capacitors are individually connected to a voltage source of 1 V, the energy stored in the capacitor C₂ is 4 times that in C₁. If these capacitors are connected in series, their effective capacitance will be

Asked in JEE Main 8th Jan 1st Shift 2020 · Series and parallel combinations

Answer: (1) 1.6 μ F

Step-by-step solution

At the same voltage U=1/2CV², so the energies are in the ratio of the capacitances: C₂=4C₁.

With C₁+C₂=10 μ F, 5C₁=10, so C₁=2 μ F and C₂=8 μ F.

In series, Cₛ=(C₁C₂)/(C₁+C₂)=(2×8)/(10)=1.6 μ F.

Why the other options are wrong

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