## 27 October 2019

### Capacitor ( Function of capacitor )

• The capacitor is defined as the conducting plates separated by dielectric material.
• The function of capacitor is to store electricity in which excess electrons on one plate and deficit electrons on other plate.
• When direct voltage is given to capacitor, charge is stored in the dielectric material.
• The stored charge is directly proportional to applied voltage.
q a V
q = CV
C = q / V
Where q = Charge
V = Applied voltage
C = Constant, a capacitance

• Therefore the capacitance is defined as the charge per unit voltage. Its unit is coulomb per voltage or farad in SI unit.

OR
• Capacitance C = eA / d

Where
d = Distance between two plates
A = Area of plates
e = Permittivity of material
• The capacitance of capacitor depends upon area of plate and distance between two plates.
• As the distance between two plates increases, the capacitance decreases and vice versa.
• The permittivity of air is taken as unity.

e = eoer
eo = Absolute permittivity
er = Relative permittivity
• The relative permittivity of any material is defined as the ratio of permittivity of any material to the permittivity of air.
er = e / eo