The electric field of a plane electromagnetic wave varies with time of amplitude $2\, Vm^{-1}$ propagating along $z$ -axis. The average energy density of the magnetic field  (in $J\, m^{-3}$) is 

  • A

    $13.29 \times 10^{-12}$

  • B

    $8.86 \times 10^{-12}$

  • C

    $17.72 \times 10^{-12}$

  • D

    $4.43 \times 10^{-12}$

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