Question

An electric dipole consists of two unlike charges of magnitude 2 × 10⁻⁶ C each and separated by 4 cm. The dipole is placed in an external electric field of 10⁵ N/C. Calculate the work done by an external agent to turn the dipole through 180°.

Answer 1

Given: q = 2 × 10⁻⁶ C

2l = 4 cm = 4 × 10⁻² m

E = 10⁵ N/C

θ = 180° + θ₀

Let us assume the dipole is initially aligned parallel to the field, i.e., θ₀ = 0.

Then,

θ = 180°

The work done by an external agent,

W = pE (l − cos θ)

= q(2l) E (1 − cos 180°)

= 2 × 10⁻⁶ C (4 × 10⁻² m) (10⁵ N/C) (1 − 1)

= 16 × 10⁻² J