Question

Two parallel metal plates having charges $+Q$ and $-Q$ face each other at a certain distance between them. If the plates are now dipped in kerosene oil tank, the electric field between the plates will

• A. become zero
• B. increase
• C. decrease
• D. remain same

Answer 1

Answer: (C)

The electric field between two charged parallel plates placed in air is
$E=\frac{\sigma }{{\epsilon }_0}=\frac{Q}{{\epsilon }_{0}A}$ ...(i)
When the parallel plates are immersed in kerosene oil tank of dielectric constant $K$, the electric field between the plates is
$E^{\prime }=\frac{\sigma }{K{\epsilon }_0}=\frac{Q}{K{\epsilon }_{0}A}=\frac{E}{K}$ (Using (i))
$\therefore \frac{E^{\prime }}{E}=\frac{1}{K}$
As $K>1$, so $E^{\prime }<E$