Question

The potential difference between the two plates of a parallel plate capacitor is constant. When air between the plates is replaced by dielectric material, the electric field intensity :

• A. Decreases
• B. Remains unchanged
• C. Becomes zero
• D. Increases

Answer 1

Answer: (A)

Decreases

In general capacitance of parallel plate capacitor is given by:
$C=\frac{k{ϵ}_{0}A}{d}$
where C is capacitance, k is relative permittivity of dielectric material, ${ϵ}_0$ is permittivity of free space constant, A is area of plates and d is distance between them.

Therefore, the capacitance of parallel plates is increased by the insertion of a dielectric material. Further, the capacitance is inversely proportional to the electric field between the plates, and hence the presence of the dielectric decreases the effective electric field.