why does store engery not change?
A capacitor stores energy rather than charge because the electric field that is created between its two plates when a voltage is applied serves as the mechanism that allows it to do so.
Two conducting plates and an insulating substance known as a dielectric separate two capacitor plates.
Whenever charges of opposite polarity are separated, electrical energy is stored within the capacitor by the same charge present within it.
So a capacitor stores energy but not charge.