A point charge Q is kept fixed on a table and another particle of charge q and mass m is to be placed in air in such a way that it remains suspended at the same location in a state of equilibrium. What should be the distance of particle from point charge fixed on table?

Explanation

To solve the problem, we need to find the distance \( r \) at which the charge \( q \) must be placed from the fixed charge \( Q \) so that it remains suspended in equilibrium.

### Step-by-Step Solution:

1. **Understanding Forces Acting on Charge \( q \)**:
- The charge \( q \) experiences two forces:
- The gravitational force acting downwards, \( F_g = mg \) (where \( m \) is the mass of charge \( q \) and \( g \) is the acceleration due to gravity).
- The electrostatic force acting upwards due to the charge \( Q \), which we will denote as \( F_e \).
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