Question

A 200 pF capacitor is charged by a 100V power supply. It is now disconnected from the power supply and connected
to an identical uncharged capacitor. How much electrostatic energy is lost in this process?​

Answer 1

Given info : A 200 pF capacitor is charged by a 100V power supply. it is now disconnected from the power supply and connected to an identical uncharged capacitor.

To find : Electrostatic energy lost in this process is..

solution : charged stored in the capacitor just before disconnecting from the power supply, Q = CV = 200pF × 100V = 2 × 10⁴ × 10¯¹² C

= 2 × 10^-8 C

so electrostatic energy stored in capacity, U₁ = 1/2 CV² = 1/2 × 2 × 10¯¹⁰ × 10⁴ = 10¯⁶ J

now capacitor is connected with another identical uncharged capacitor.

so, charge shares by each of them is half of 2 × 10^-8C

i.e., charge on each capacitor = 10^-8 C

now equivalent capacitance of these two capacitor is given as,

1/Ceq = 1/200pF + 1/200pF = 1/100pF

⇒Ceq = 10¯¹⁰ C

now electrostatic energy stored in capacitors is given as U₂ = 1/2 CeqV²

= 1/2 × 10¯¹⁰ × (100)²

= 0.5 × 10¯⁶ J

So the electrostatic energy lost in this process = U₁ - U₂ = 1 × 10¯⁶ - 0.5 × 10¯⁶ = 0.5 × 10¯⁶ J

Answer 2

i hope you understand it.