A cylindrical capacitor has charge Q and length L. If both the charge and length of the capacitor are doubled by keeping other parameters fixed, the energy stored in the capacitor

Options

A. Remains same
B. Increases two times
C. Decreases two times
D. Increases four times

Answer

B

Explanation

Capacitance of a cylindrical capacitor `=(2pi epsilon_0L)/(ln (b//a))`
Energy stored in the capacitor 
`U=(Q^2)/(2C)=1/2(Q^2ln (b//a))/(2pi epsilon_0L)`
`Uprop Q^2/L`
`Q. = 2Q , L. =2L`
`(U.)/U=(((2Q)^2)/(2L))/(Q^2//L)=2:1`