Statement I: A parallel plate capacitor is charged to a potential difference of 100 V, and disconnected from the voltage source. A slab of dielectric is then slowly inserted between the plates. Compared to the energy before the slab was inserted, the energy stored in the capacitor with the dielectric is decreased. Statement II: When we insert a dielectric between the plates of a capacitor, the induced charges tend to draw in the dielectric into the field (just as neutral objects are attracted by charged objects due to induction). We resist this force while slowly inserting the dielectric, and thus do negative work on the system, removing electrostatic energy from the system.

Question

Statement I: A parallel plate capacitor is charged to a potential difference of 100 V, and disconnected from the voltage source. A slab of dielectric is then slowly inserted between the plates. Compared to the energy before the slab was inserted, the energy stored in the capacitor with the dielectric is decreased. Statement II: When we insert a dielectric between the plates of a capacitor, the induced charges tend to draw in the dielectric into the field (just as neutral objects are attracted by charged objects due to induction). We resist this force while slowly inserting the dielectric, and thus do negative work on the system, removing electrostatic energy from the system. (A) If both statements are true and statement II is the correct explanation of statement I. (B) If both statements are true but statement II is not the correct explanation of statement I. (C) If statement I is true but statement II is false. (D) If both statements are false.

Tardigrade Admin · Accepted Answer

In an isolated charged capacitor, the potential energy stored is decreased on insertion of dielectric because in expression U=(Q2/2 C), C increases on insertion of dielectric.

If both statements are true and statement II is the correct explanation of statement I.

If both statements are true but statement II is not the correct explanation of statement I.

If statement I is true but statement II is false.

If both statements are false.

In an isolated charged capacitor, the potential energy stored is decreased on insertion of dielectric because in expression U=2CQ2​,C increases on insertion of dielectric.

In an isolated charged capacitor, the potential energy stored is decreased on insertion of dielectric because in expression $U = \frac{Q ^{2}}{2 C}, C$ increases on insertion of dielectric.