Two point charges repel each other with a force F when placed in water of dielectric constant 81. What will be the force between them when placed the same distance apart in air ?

Explanation

To solve the problem, we need to determine the force between two point charges when they are placed in air, given that they repel each other with a force \( F \) when placed in water with a dielectric constant of \( 81 \).

### Step-by-Step Solution:

1. **Understanding the Forces in Different Media**:
The force between two point charges in a medium is given by Coulomb's law:
\[
F = \frac{k \cdot Q_1 \cdot Q_2}{r^2}
...