## What is Parallel Plate Capacitor?

It is an arrangement used for storing electric charge and hence electric energy.

## Principle of Parallel Plate Capacitor:

When we bring uncharged earth connected rod near the charged rod, the capacity of the charged rod increases.

## Construction and Theory of Parallel Plate Capacitor:

It consists of two plates X and Y, held parallel with each other. The area of each plate is ‘A’ and the distance between them is ‘d’. Plate Y is earth connected and X plate is fully charged.

Plate X is given +Q charge, due to the phenomenon of induction -Q charge is induced on the inner side of plate Y. Due to this electric field E is set up between the plates which are given by-

E = σ/ε_{0}Where σ is surface charge density and (σ = Q/A)⇒ E = Q/Aε _{0}But we know, V = E x d = Q/Aε _{0} x dThe capacity of parallel plate capacitor is given by- C = Q/V = Q x Aε _{0}/Qd ⇒ C = Aε _{0}/d ……………….(I) |

Hence the capacity of the capacitor depends upon the following three factors-

- Area of plates.
- Distance between plates.
- Nature of medium separating the two plates.

When the plates of the capacitor are separated by some dielectric medium (like mica sheet) of dielectric constant K or relative permittivity ε_{r}, then-

C_{m} = KAε_{0}/d = Aε_{0}ε_{r}/d ……………..(II)From (I) and (II)- C _{m} = K x C |

i.e. capacity becomes K times capacity with air/Vaccum as the dielectric.