An electric dipole of moment p is placed in the position of stable equilibrium in uniform electric field of intensity E. This is rotated through an angle θ from the initial position. The potential energy of the electric dipole in the final position is (a) -pEcos θ (b) pE(1 - cos θ) (c) pEcos θ (d) pEsin θ

Answer: (a). Potential energy of a dipole: U = - p · E = -pEcos θ, where θ is the angle between p and E. Starting from stable equilibrium ( θ = 0) and rotating by θ, the angle becomes θ. So the answer is (a) -pEcos θ.

An electric dipole of moment p is placed in the position of stable… | NEET 1994 (AIPMT)

Q79NEET 1994 · AIPMTMedium

Electric Dipole

An electric dipole of moment $p$ is placed in the position of stable equilibrium in uniform electric field of intensity $E$ . This is rotated through an angle $\theta$ from the initial position. The potential energy of the electric dipole in the final position is

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Answer: (a)

Potential energy of a dipole: $U = -\vec p \cdot \vec E = -pE\cos\theta$ , where $\theta$ is the angle between $\vec p$ and $\vec E$ .
Starting from stable equilibrium ( $\theta = 0$ ) and rotating by $\theta$ , the angle becomes $\theta$ .
So the answer is (a) $-pE\cos\theta$ .

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