Physics Class 12 NCERT Solutions: Chapter 2 Electrostatic Potential and Capacitance Part 4

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Electrostatic energy

Electrostatic Energy

Q: 9. Explain what would happen if in the capacitor given in Exercise (Reference: Chapter 2 Electrostatic Potential And Capacitance Part 3), a thick mica sheet (of dielectric constant ) was inserted between the plates,

(A) While the voltage supply remained connected.

(B) After the supply was disconnected.


(A) Dielectric constant of the mica sheet,

Initial capacitance,

New capacitance,

Supply voltage,

New charge,

Potential across the plates remains .

(B) Dielectric constant,

Initial capacitance

New capacitance,

If supply voltage is removed, then there will be no effect on the amount of charge in the plates.


Potential across the plates is given by,

Q: 10. Capacitor is connected to a battery. How much electrostatic energy is stored in the capacitor?


Capacitor of the capacitance,

Potential difference,

Electrostatic energy stored in the capacitor is given by the relation;

Therefore, the electrostatic energy stored in the capacitor is.

Q: 11. A capacitor is charged by a supply. It is then disconnected from the supply and is connected to another uncharged capacitor. How much electrostatic energy is lost in the process?


Capacitance of the capacitor,

Potential difference,

Electrostatic energy stored in the capacitor is given by,

If supply is disconnected from the capacitor and another capacitor of capacitance is connected to it, then equivalent capacitance of the combination is given by

New electrostatic energy can be calculated as

Loss in electrostatic energy

Therefore, the electrostatic energy lost in the process is .

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