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Two capacitors C₁ and C₂ are charged to 120 V and 200 V respectively. It is found that by connecting them together the potential on each one can be made zero. Then

Asked in JEE Main 2013 · Redistribution of charge

• (1) 9C₁=4C₂
• (2) 5C₁=3C₂
• (3) 3C₁=5C₂
• (4) 3C₁+5C₂=0

Step-by-step solution

Why the other options are wrong

• (1) Not reachable from 120 V and 200 V: equating the stored energies gives 9C₁=25C₂, and 9C₁=4C₂ would need the two voltages in the ratio 2:3, so this option is a printed filler.
• (2) Inverts the relation: equal charges mean C∝1/V, so the capacitor at the lower voltage must be the larger one.
• (4) A sum of two positive capacitances can never be zero; the cancellation is of charge, not of capacitance.

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