Q 12-02-152JEE MainJEE Main 2020 (7 Jan, Shift 2)Easy
A $60$ pF capacitor is fully charged by a $20$ V supply. It is then disconnected from the supply and is connected to another uncharged $60$ pF capacitor in parallel. The electrostatic energy that is lost in this process by the time the charge is redistributed between them is (in nJ) ______.
Numerical value type. Enter your answer.
Answer: 6
Initial energy: $\tfrac12CV^2 = \tfrac12\times60\times10^{-12}\times400 = 12$ nJ.
The charge $Q = CV$ is shared by $2C$, so the common voltage is $10$ V and the final energy is $\tfrac12(2C)(10)^2 = 6$ nJ.
Energy lost $= 12 - 6 = 6$ nJ.
Solution by Sreeraj P, M.Sc Physics