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J & K CET Engineering J and K - CET Engineering Solved Paper-2008

  • question_answer
    The dipole moment of a dipole in an uniform external field \[\vec{E}\] is \[\vec{P}\]. Then, the torque \[(\tau )\] acting on the dipole is

    A)  \[\vec{\tau }=\vec{P}\times \vec{E}\]

    B)  \[\vec{\tau }=\vec{P}.\vec{E}\]

    C)  \[\vec{\tau }=2(\vec{P}+\vec{E})\]

    D)  \[\vec{\tau }=(\vec{P}+\vec{E})\]

    Correct Answer: A

    Solution :

    Torque \[(\tau )\] acting on the dipole in an uniform external field \[\vec{E}\] \[\tau =\]either force \[\times \] perpendicular distance \[=qE=\,2\,a\,\sin \,\theta \] \[(q\times 2a)\times E\,\,\sin \,\theta \] \[=PE\,\,\sin \,\theta \] or \[\vec{\tau }=\vec{P}\times \vec{E}\]


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