(i) Derive the expression for electric field at a point on the equatorial line of an electric dipole.
(ii) Depiet the orientation of the dipole in (i) stable, (ii) unstable equilibrium in a uniform electric field.

Explanation

### Step-by-Step Solution

#### (i) Deriving the Expression for Electric Field at a Point on the Equatorial Line of an Electric Dipole

1. **Understanding the Dipole Configuration**:
- Consider an electric dipole consisting of two charges, +q and -q, separated by a distance of 2a. The dipole moment \( \vec{p} \) is defined as \( \vec{p} = q \cdot 2a \).

2. **Identifying the Point of Interest**:
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