Equivalent resistance of the circuit, Req = (12||18) + 8 Req = 7.2 + 8 Req = 15.2 ohm Source current = current through 8 ohm resistor, I = Vr/R8 I = 20/8 I = 2.5 A Supply votage V = I*Req V = 2.5*15.2 V = 38 V
The relation between electric intensity E, voltage applied V and the distance d between the plates of a parallel plate condenser is given by: V = E*L E = V/L