13) Capacitance per unit length between two parallel wires of radius r and separated by distance ‘d’:

                           Fig (9)

14) The energy stored in a fully charged capacitor:

   E² = Energy density.

Where E is electric field in a capacitor.

15) Charging and discharging of capacitors:

(a)

                   Fig (10)

(b)

                 Fig (11)

V_C = E at t=0.

(c)

                       Fig (12)

(d)

                Fig (13)