Question

When a dielectric material is introduced between the plates of a charged condenser, after disconnecting the battery, the electric field between the plates:

• A. decreases
• B. increases
• C. does not change
• D. may increase or decrease

Answer 1

Answer: (A)

decreases

We know electric field between capacitor plates: $E=\frac{\sigma }{{ϵ}_0}$$=\frac{V}{d}$, where $d$ is the distance between the plates.

When battery is disconnected, the change present on capacitor is fixed, i.e., $V$ is constant.

Now, when the dielectric is introduced, the electric field becomes: $E^{\prime }=\frac{V}{Kd}$, where K is dielectric constant which is always > 1

$\therefore$ electric field decreases.