JEE Main & Advanced JEE Main Paper (Held On 9 April 2017)

  • question_answer
    The electric field component of a monochromatic radiation is given by \[\vec{E}=2{{E}_{0}}\hat{i}\,\cos kz\,\cos \omega t\] Its magnetic field \[\vec{B}\]  [JEE Online 09-04-2017]

    A)  \[\frac{2{{E}_{0}}}{c}\hat{j}\,\sin kz\,\sin \omega t\]

    B)  \[\frac{2{{E}_{0}}}{c}\hat{j}\cos kz\,\cos \omega t\]

    C)  \[\frac{2{{E}_{0}}}{c}\hat{j}\sin kz\,\cos \omega t\]

    D)  \[-\frac{2{{E}_{0}}}{c}\hat{j}\sin kz\,\sin \omega t\]

    Correct Answer: A

    Solution :

                    \[\frac{dE}{dz}=-\,\frac{dE}{dt}\] \[\frac{dE}{dz}=-\,2{{E}_{0}}\,K\,\sin \,kz\,\cos \omega t\,=-\frac{dB}{dt}\] \[dB=+2{{E}_{0}}K\,\sin kz\,\cos \omega t\,dt\] \[B=+2{{E}_{0}}K\,\sin kz\,\int_{{}}^{{}}{\cos \,\omega tdt}\] \[=+2{{E}_{0}}\,\frac{k}{\omega }\,\sin \,kz\,\sin \omega t\] \[\frac{{{E}_{0}}}{{{B}_{0}}}=\frac{\omega }{k}=C\] \[B=\frac{2{{E}_{0}}}{C}\sin \,kz\,\sin \omega t\]


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