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/(C_(eq)) = (1/12+1/12) Pf rArr C_(eq) = 6xx 10^(-12)F`
Electrostatic energy stored is `1/2 C_(eq)V^(2) = 1/2 xx 6 xx 10^(-12) xx 50^(2) = 7.5 xx 10^(-9) J`
Charge drawn from the battery `=Q = 6 xx 10^(-12) xx 50 = 3 xx 10^(-9) J`
In parallel `C_(eq) = C_(1) xx C_(2) = 12 + 12 = 24 pF`
Energy stored `= 1/2C_(eq) V^(2) = 1/2 xx 24 xx 10^(-12) xx 50^(2) = 3 xx 10^(-8) J`
Charge drawned from battery `Q = C_(eq) V = 24 xx 10^(-12) xx 50 = 1.2 xx 10^(-9) C`.