Question

An electric dipole is held in a uniform electric field. (i) Show that the net force acting on it is zero. (ii) The dipole is aligned parallel to the field. Find the work done by rotating it through the angle of 180°. [CBSE (AI) 2012]

January 21, 2024

Answer

(i) The dipole moment |P| = q × 2a

Force on -q at A = -qE

Force on +q at B = +qE

Net force on the dipole = qE – qE = 0

(ii) We know that work done in rotating an electric dipole from θ₁ to θ₂, (where θ 1 is the angle of the dipole with electric field) is given by,

W = pE (cos θ₁ − cos θ₂) now given θ₁ = 0º, θ₂ = 180º

∴ W = pE(cos 0 − cos 180) = 2pE

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