Question

Force of 80 Newton works between two point charges placed at a fixed distance apart in air. When these charges are placed at the same distance apart in a dielectric medium, then the force of 8 Newton works on it. The dielectric constant of the medium will be: 
 

• A. \( K = -10 \)
• B. \( K = 10 \)
• C. \( K = 0.01 \)
• D. \( K = -0.01 \)

Hint:

The force between two charges decreases in a dielectric medium by a factor equal to the dielectric constant \( K \), which is always greater than 1 for materials other than air.

Answer 1

The Correct Option is B

The force between two point charges is related to the dielectric constant \( K \) of the medium by the formula: \[ F_{\text{medium}} = \frac{F_{\text{air}}}{K}. \] Given that the force in air is 80 N and the force in the dielectric medium is 8 N: \[ 8 = \frac{80}{K} \quad \Rightarrow \quad K = \frac{80}{8} = 10. \]