An oil drop of mass ` m` carrying charge - Q is to be held stationary in the gravitational field of the earth. What is the magnitude and direction of the electrostatic field required for this purpose ?

Explanation

To solve the problem of holding an oil drop of mass \( m \) carrying charge \( -Q \) stationary in the gravitational field of the Earth, we need to analyze the forces acting on the drop.

### Step-by-Step Solution:

1. **Identify the Forces Acting on the Oil Drop**:
- The oil drop experiences a gravitational force acting downward, which is given by:
\[
F_g = mg
...