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Electric Charges And Fields

Question

Find the amount of work done in rotating a dipole of dipole moment 3 x 10^–3 cm from its position of stable equilibrium to the position of unstable equilibrium, in a uniform electric field of intensity 10⁴ NC^–1.

Solution

In rotating the dipole from the position of stable equilibrium by an angle θ, the amount of work done,

W = PE (1 - \cos θ)

For unstable equilibrium

θ = 180 °

∴ W = PE (1 - \cos 180 °) [\cos 180 ° = - 1]

= 2 PE

= 2 \times 3 \times 10^{- 3} \times 10^{4} J = 60 J .