Practice portal › Electric Potential and Capacitance › Capacitor Circuits and Energy
Asked in GSEB Board July 2017 · Redistribution of charge
Given: capacitor C with charge Q and energy U = (Q²)/(2C); after the battery is removed it is joined in parallel to an identical uncharged capacitor.
Idea: with no battery, the total charge Q is conserved and is shared.
Identical capacitors in parallel share it equally: Q/2 each, at a common voltage V/2.
Energy of each: ((Q/2)²)/(2C) = 1/4·(Q²)/(2C) = U/4.
The total is now U/2: the other half of U is lost as heat (and radiation) while the charge flows through the connecting wires.
So each capacitor has energy U/4.
Reading this solution needs no sign-in. You only sign in to practise against the clock and keep your progress.
Practise this with a timer