Question

On inserting a dielectric material between two positive charges in air, the value of repulsive force will

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

Hint:

Dielectric materials reduce the effective force between charges by increasing the permittivity of the medium.

Answer 1

The Correct Option is B

Step 1: Coulomb's Law.
The repulsive force between two charges is given by Coulomb’s law: \[ F = \frac{1}{4\pi \epsilon_0} \cdot \frac{q_1 q_2}{r^2} \] where \( F \) is the force, \( q_1 \) and \( q_2 \) are the magnitudes of the two charges, and \( r \) is the distance between them. The constant \( \epsilon_0 \) is the permittivity of free space.
Step 2: Effect of dielectric material.
When a dielectric material is inserted between two positive charges, the permittivity of the medium increases, and as a result, the electrostatic force between the charges decreases. The dielectric constant reduces the effective force.
Step 3: Explanation of each option.
- (A) Increase: Incorrect. The force will not increase; it decreases due to the dielectric.
- (B) Decrease: Correct. The dielectric reduces the force between the charges.
- (C) Remain same: Incorrect. The presence of a dielectric changes the electrostatic force.
- (D) Become zero: Incorrect. The force does not become zero; it decreases.
Step 4: Conclusion.
Inserting a dielectric material decreases the repulsive force between the charges.