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 = e_oe_r

        e_o = Absolute permittivity

         e_r = Relative permittivity

• The relative permittivity of any material is defined as the ratio of permittivity of any material to the permittivity of air.

        e_r = e / e_o        

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