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A plane electromagnatic wave, has frequency of 2.0 \times 10^{10}Hz and its energy density is 1.02 \times 10^{-8}\;J/m^{3} in vacuum. The amplitude of the magnetic field (in  nT )  of the wave is close to \left ( \frac{1}{4\pi \varepsilon _{0}}=9\times 10^{9}\frac{Nm^{2}}{C^{2}} and \; speed \; of \; light=3\times 10^{8}ms^{-1}\right )
Option: 1 160
Option: 2 150
Option: 3 180
Option: 4 190

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best_answer

\begin{array}{l} \text { Energy density }= \frac{\mathrm{dU}} {\mathrm{dV}}=\frac{\mathrm{B}_{0}^{2}}{2 \mu_{0}} \\\\ 1.02 \times 10^{-8}=\frac{\mathrm{B}_{0}^{2}}{2 \times 4 \pi \times 10^{-7}} \\ \\ \mathrm{~B}_{0}^{2}=\left(1.02 \times 10^{-8}\right) \times\left(8 \pi \times 10^{-7}\right) \\ \Rightarrow \mathrm{B}_{0}=16 \times 10^{-8} \mathrm{~T}=160 \mathrm{nT} \end{array}

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avinash.dongre

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