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An electric dipole of moment $\vec p$ is placed in a uniform external field $\vec E$. The torque on it is:
A$pE\cos\theta$
B$pE / \sin\theta$
C$\vec p \times \vec E$
D$\vec p \cdot \vec E$
Answer & Solution
Correct answer: C. $\vec p \times \vec E$
Torque on a dipole in a uniform field is $\vec\tau = \vec p \times \vec E$, magnitude $pE\sin\theta$, which tends to align $\vec p$ with $\vec E$.