Question

The circular plates A and B of a parallel
plate air capacitor have a diameter of
0.1 m and are 2 x 10-ºm apart. The
plates C and D of a similar capacitor
have a diameter of 0.12 m and are 3 x
10-3 m apart. Plate A is earthed. Plates
B and D are connected together. Plate
A is earthed. Plates B and D are
connected together. Plate C is
connected to the positive pole of a 120
V battery whose negative is earthed.
The energy stored in the system is​

Answer 1

Answer:

capacitance of capacitor AB, C1 = (A∈0/d1)

capacitance of capacitor CD, C2 = [(A2∈0)/d2]

combined capacitance : C = [(C1C2)/(C1 + C2)] = [(A1A2∈0) / (A1d1 + A2d1)]

∴ C = [(π∈0r12r22)/(r12d2 + r22d1)]

= π∈0[{(5 × 10–2)2 (6 × 10–2)2}/{(5 × 10–2)2 × 3 × 10–3 + (6 × 10–2)2 × 2 × 10–3}]

= (30/49)π∈0

Energy stored = U = (1/2)CV2

= (1/2) [(30/49)π∈0] (120)2

= 0.1224 × 10–6

= 0.12μ