CBSE Class 12 · 2005 · CapacitanceShort Answer

WhatsApp Email

(a) Why does the electric field inside a dielectric decrease when it is placed in an external electric field?
(b) A parallel plate capacitor with air between the plates has a capacitance of 8 pF. What will be the capacitance if the distance between the plates is reduced by half and the space between them is filled with a substance of dielectric constant

K = 6

Solution

(a) In an external field the dielectric gets polarised; the bound charges on its surfaces set up an induced field opposite to the applied field.
The net field inside is therefore

E = E_{0} / K

, smaller than the applied field.
(b) The air-filled capacitance is:

C_{0} = \frac{ε _{0} A}{d} = 8 pF

With the separation halved

(d \to d /2)

and a dielectric

K = 6

filling it:

C = \frac{K ε _{0} A}{d /2} = 2 K C_{0} = 2 \times 6 \times 8

C = 96 pF

CBSE Class 12 Board · 2005 · Subjective

Practise more: all CBSE board PYQs on Capacitance →

More board questions on Capacitance

\textit{Case study — dielectrics in capacitors:} A dielectric slab placed in an external field develops opposite bound charges on its faces, setting up an internal field; this raises a capacitor's capacitance and alters its stored energy. Which of the following is a polar molecul …
CBSE 2024View solution →
Which of the following statements about dielectrics is correct?
CBSE 2024View solution →
When a dielectric slab is inserted between the plates of an \emph{isolated} charged capacitor, the energy stored in it
CBSE 2024View solution →
An air-filled capacitor with plate area $A$ and plate separation $d$ has capacitance $C_{0}$ . A slab of dielectric constant $K$ , area $A$ and thickness $\frac{d}{5}$ is inserted between the plates. The capacitance becomes
CBSE 2024View solution →
Two capacitors of capacitances $2 C_{0}$ and $6 C_{0}$ are first connected in series and then in parallel across the same battery. The ratio of the energy stored in the series combination to that in the parallel combination is
CBSE 2024View solution →
A parallel plate capacitor (A) of capacitance $C$ is charged by a battery to voltage $V$ . The battery is disconnected and an uncharged capacitor (B) of capacitance $2 C$ is connected across A. Find the ratio of (i) final charges on A and B, and (ii) total electrostatic energy stor …
CBSE 2023View solution →