CBSE Class 12 · 2024 · CapacitanceMultiple Choice

When a dielectric slab is inserted between the plates of an \emph{isolated} charged capacitor, the energy stored in it

(A)Increases and the electric field inside it also increases.
(B)Decreases and the electric field also decreases.✓ Correct
(C)Decreases and the electric field increases.
(D)Increases and the electric field decreases.

Answer: (B)

Solution

The capacitor is isolated, so the charge

Q

is constant. Inserting a dielectric raises the capacitance to

C = K C_{0}

, so the field

E = \frac{E _{0}}{K}

decreases and the stored energy

U = \frac{Q ^{2}}{2 C}

decreases. Both decrease — option (B).

CBSE Class 12 Board · 2024 · Single correct option

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