Question

Two point charges exert on each other a force F, when they are placed r distance apart in air. When they are placed R distance apart in medium of dielectric constant K, they exert the same force. The distance R equals
1. \(\frac{r}{\sqrt K}\)
2. \(\frac{r}{K}\)
3. rK
4. \(r\sqrt K\)

Answer 1

Correct Answer - Option 1 : \(\frac{r}{\sqrt K}\)

The correct answer is \(\frac{r}{\sqrt K}\)

• Given two point charges exert a force F when placed r apart in constant K, the force between them is the same. We have to find R.
• let q₁ and q₂ be two point charges.
• 1/4πE₀q₁*q₂/r2 = 1/4πE₀q₁*q₂/K*R² (where E0= permittivity of air and K = dielectric constant)
• 1/r² = 1/K*R²
• R= \(\frac{r}{\sqrt K}\)