Question

Two identical capacitors of 12 pF each are connected in a series across a battery of 50V. How much electrostatic energy is stored in the combination ? If these were connected in parallel across the same battery , how much energy will be stored in combintion now ? Also find the charge drawn from the battery in each case.

Answer 1

In series combination:

1 / Ceq  = [1/12 + 1/12] Pf  ⇒ Ceq = 6 x 10-12 F

Electrostatic energy stored is ½ Ceq V2 = 1/2 x 6 x 10-12  x 502  = 7.5 x 10-9J

Charge drawn from the battery = Q = 6 x 10-12 x 50 = 3 x 10-10C

In Parallel Ceq = C1 +C2 = 12+12 = 24pF

Energy Stored = ½ Ceq V2  = 1/2 x 24 x 10-12  x 502  = 3 x 10-8J

Charge drawned from battery Q = Ceq V = 24 x 10-12 x 50 = 1.2 x 10-9C.