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/ε0 Where σ is surface charge density and (σ = Q/A) ⇒ E = Q/Aε0 But we know, V = E x d = Q/Aε0 x d The capacity of parallel plate capacitor is given by- C = Q/V = Q x Aε0/Qd ⇒ C = Aε0/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 εr, then-
Cm = KAε0/d = Aε0εr/d ……………..(II) From (I) and (II)- Cm = K x C
i.e. capacity becomes K times capacity with air/Vaccum as the dielectric.
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