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8.Electromagnetic waves
easy
The electric field of plane electromagnetic wave of amplitude $2\,V/m$ varies with time, propagating along $z-$ axis. The average energy density of magnetic field (in $J/m^3$ ) is
A
$13.29 \times 10^{-12}$
B
$8.85 \times 10^{-12}$
C
$17.72 \times 10^{-12}$
D
$4.43 \times 10^{-12}$
Solution
$\left\langle {{{\rm{u}}_{\rm{B}}}} \right\rangle = \left\langle {{{\rm{u}}_{\rm{E}}}} \right\rangle $
$=\frac{1}{4} \varepsilon_{0} \mathrm{E}_{0}^{2}=\frac{1}{4} \times 8.85 \times 10^{-12}(2)^{2} $
$=8.85 \times 10^{-12} \mathrm{\,J} / \mathrm{m}^{3} $
Standard 12
Physics
