A capacitor is charged by connecting a battery across its plates. It stores energy U. now the battery is disconnected and another identical capacitor is connected across it. What will be the energy stored by both capacitors of the system?

Options

A. `U/2`
B. `2U`
C. `(3)/(2)U`
D. U

Answer

A

Explanation

Energy with one capacitor is `U=(1)/(2)(q^(2))/(C)`
When the battery is disconnected, then charge (q) remains constant. When another identical capacitor is joined across it, the equivalent capacitance becomes `C'=2C`.
`therefore U'=(1)/(2)(q^(2))/(2(2C))=(1)/(2)U`
Thus, `U'=(U)/(2)`