JEE Main & Advanced Physics EM Waves JEE PYQ-Electro Magnetic Waves

  • question_answer
    An electromagnetic wave travelling in the x-direction has frequency of \[2\times {{10}^{14}}Hz\]and electric field amplitude of \[27V{{m}^{-1}}.\]From the options given below, which one describes the magnetic field for this wave? [JEE ONLINE 10-04-2015]

    A) \[\overset{\to }{\mathop{B}}\,(x.t)=(9\times {{10}^{-8}}T)\hat{i}\]\[\sin \left[ 2\pi (1.5\times {{10}^{-8}}x-2\times {{10}^{14}}t) \right]\]

    B) \[\overset{\to }{\mathop{B}}\,(x,t)=(3\times {{10}^{-8}}T)\hat{j}\] \[\sin \left[ 1.5\times {{10}^{-6}}x-2\times {{10}^{14}}t) \right]\]

    C) \[\overset{\to }{\mathop{B}}\,(x,t)=(3\times {{10}^{-8}}T)\hat{j}\]\[\sin \left[ 2\pi (1.5\times {{10}^{-8}}x-2\times {{10}^{14}}t) \right]\]

    D) None of these

    Correct Answer: D

    Solution :

    (*)Enwove
    \[f=2\times {{10}^{14}}Hz\]
    \[{{E}_{0}}=27V/m\]
    We know \[\to \frac{E}{B}=C\]
    So \[B=\frac{27}{3\times {{10}^{8}}}=9\times {{10}^{-8}}T\]
    now for \[\lambda =\frac{3\times {{10}^{8}}}{2\times {{10}^{17}}}=1.5\times {{10}^{-6}}m\]
    so \[B=9\times {{10}^{-8}}\]
    \[\sin \left( 2\pi \left[ \left( \frac{1}{1.5\times {{10}^{-6}}} \right)x-2\times {{10}^{14}}t \right] \right)\hat{k}\]


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