Q64 / 90 · JEE Main 2012 (Offline) · Physics

An electromagnetic wave in vacuum has the electric and magnetic fields $\vec{E}$ 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 $\overrightarrow{\mathrm{k}}$. Then :

  • A
    $\vec{X} \| \vec{B}$ and $\vec{k} \| \vec{B} \times \vec{E}$
  • B
    $\vec{X} \| \vec{E}$ and $\vec{k} \| \vec{E} \times \vec{B}$
  • Correct answer
    C
    $\vec{X} \| \vec{B}$ and $\vec{k} \| \vec{E} \times \vec{B}$
  • D
    $\vec{X} \| \vec{E}$ and $\vec{k} \| \vec{B} \times \vec{E}$

Solution

Direction of polarization is parallel to magnetic field, $\therefore \quad \overrightarrow{\mathrm{X}} \| \overrightarrow{\mathrm{B}}$ and direction of wave propagation is parallel to $\overrightarrow{\mathrm{E}} \times \overrightarrow{\mathrm{B}}$ $\therefore \quad \overrightarrow{\mathrm{K}} \| \overrightarrow{\mathrm{E}} \times \overrightarrow{\mathrm{B}}$

Hence, the correct answer is option: 'C'.

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