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JEE Main & Advanced Sample Paper JEE Main - Mock Test - 42

  • question_answer
    An electromagnetic wave in vacuum has the electric and magnetic field \[\vec{E}\] and \[\vec{B},\] which are always perpendicular to each other. The direction of polarization is given by \[\vec{X}\] and that of wave propagation by \[\vec{k}\]. Then

    A) \[\vec{X}||\vec{B}\] and \[\vec{k}\,\,\,||\vec{B}\,\times \vec{E}\]

    B) \[\vec{X}\,\,\,||\vec{E}\] and \[\vec{k}\,\,\,||\vec{E}\times \vec{B}\]

    C) \[\vec{X}\,\,\,||\vec{B}\] and \[\vec{k}\,\,\,||\vec{E}\times \vec{B}\]

    D) \[\vec{X}\,\,\,||\vec{E}\] and \[\vec{k}\,\,\,||\vec{B}\times \vec{E}\]

    Correct Answer: B

    Solution :

    \[\because \] The E.M. wave are transverse in nature i.e., \[=\frac{\vec{k}\times \vec{E}}{\mu \omega }=\vec{H}\]             ??.(i) where \[\vec{H}=\frac{{\vec{\beta }}}{\mu }\] and \[\frac{\vec{k}\times \vec{H}}{\omega \varepsilon }=-\vec{E}\]                       .....(ii) \[\vec{k}\] is \[\bot \]\[\vec{H}\] and \[\vec{k}\] is also \[\bot \] to \[\vec{E}\] or In other words \[\vec{X}||\vec{E}\] and \[\vec{k}||\vec{E}\,\,\times \vec{B}\]


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