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The energy of a charged capacitor is U. Now it is removed from the battery and then connected to two other identical uncharged capacitors in parallel. What will be the energy of each capacitor?

Asked in GSEB Board March 2023 · Redistribution of charge

• (1) U/4
• (2) U/3
• (3) U
• (4) U/9

Step-by-step solution

Why the other options are wrong

• (1) Shares the charge between two capacitors instead of three: Q/2 each gives ((Q/2)²)/(2C)=U/4. That is the answer when only one other capacitor is added.
• (2) That is the total energy left in all three, (Q²)/(2(3C))=U/3, not each one's share. It is also what you get by assuming the original U survives and splits three ways — but energy is not conserved here: two-thirds of it is lost while the charge flows.
• (3) Assumes each capacitor ends at the original voltage V, as if the battery were still connected, so each would hold 1/2CV²=U. With the battery gone the charge Q is fixed, and the common voltage drops to V/3.

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