A $27 \mathrm{~mW}$ laser beam has a cross-sectional area of $10 \mathrm{~mm}^{2}$. The magnitude of the maximum electric field in this electromagnetic wave is given by:
[Given permittivity of space $\epsilon_{0}=9 \times 10^{-12}$ SI units, Speed of light $\mathrm{c}=3 \times 10^{8} \mathrm{~m} / \mathrm{s}$ ]
Correct Option: , 4
(4) EM wave intensity
$\Rightarrow \mathrm{I}=\frac{\text { Power }}{\text { Area }}=\frac{1}{2} \varepsilon_{0} \mathrm{E}_{0}^{2} \mathrm{c}$
[where $\mathrm{E}_{0}=$ maximum electric field]
$\Rightarrow \frac{27 \times 10^{-3}}{10 \times 10^{-6}}=\frac{1}{2} \times 9 \times 10^{-12} \times \mathrm{E}_{0}^{2} \times 3 \times 10^{8}$
$\Rightarrow \mathrm{E}_{0}=\sqrt{2} \times 10^{3} \mathrm{kV} / \mathrm{m}=1.4 \mathrm{kV} / \mathrm{m}$