Question

Assertion :The force between two electric charges in a dielectric medium is less than it would be in a vacuum. Reason: Quantity of energy stored in an electric field per unit volume of a dielectric medium is greater than that of vaccum

• A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
• B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
• C. Assertion is correct but Reason is incorrect
• D. Both Assertion and Reason are incorrect

Answer 1

The correct option is C Assertion is correct but Reason is incorrect

Force between two charges in a dielectric medium, $F=\frac{q_1{q}_2}{4\pi ϵr^2}$

where $r$ is the separation between two charges $q_1$ and $q_2$.

Permitivity of the dielectric medium and that of vacuum is $ϵ$ and ${ϵ}_o$, respectively.

And we know $ϵ>{ϵ}_o$.

$⟹$ $F<F_o$

Hence Assertion is true.

Energy stored per unit volume of dielectric medium, $E=\frac{1}{2}C{V}^2.\frac{1}{Ad}$

where $C=\frac{Aϵ}{d}$

$⟹$ $E=\frac{1}{2}\frac{ϵV^2}{d^2}$

We know $ϵ>{ϵ}_o$

$⟹$ $E>E_o$

Thus reason is incorrect.