Question

How does dielectric affect energy stored?

Answer 1

Explanation:

The capacitance of a capacitor increases and its stored energy decreases if a dielectric is placed between its plates. The energy stored as a result of the capacitor's work in removing the dielectric between the plates of the capacitor is reduced.

The energy stored in a capacitor is given by: $U=\frac{Q∆V}{2}=\frac{C∆V^2}{2}=\frac{Q^2}{2C}$.

1. As an example take a capacitor with nothing in between the plates. Capacitors are charged and isolated, ensuring a stable charge on the plates. By adding a dielectric, the capacitance increases and the energy in the capacitor decreases as evident from the above equation.
2. Since the charges on its surface are drawn towards the plates of the capacitor, the dielectric tends to remain inside the device. The dielectric between the plates is pulled down by the capacitor, reducing the amount of energy stored. The effort required to pull the dielectric back again manifests itself as an increase in the capacitor's energy reserves.