Question 227: EM waves

Question

A laser beam of cross-sectional area $5 \mathrm{~mm}^2$ is 30 mW . Find the magnitude of maximum electric field in this electromagnetic wave.

Accepted Answer

$$ \begin{aligned} &	ext {  Intensity of electromagnetic wave, }\ &I=\frac{1}{2} n c \varepsilon_0 E^2\ &\begin{aligned} & n=1, 	ext { refractive index of air } \ & I=\frac{1}{2} c \varepsilon_0 E^2 \ & I=\frac{	ext { Pressure }}{	ext { Area }} \ & \frac{p}{A}=\frac{1}{2} c \varepsilon_0 E^2 \ & E^2=\frac{2 p}{A c \varepsilon_0} \end{aligned}\ &\begin{aligned} E & =\sqrt{\frac{2 	imes 30 	imes 10^{-3}}{5 	imes 10^{-6} 	imes 3 	imes 10^8 	imes 8.85 	imes 10^{-12}}} \ & =\sqrt{\frac{60 	imes 10^{-3}}{132.7 	imes 10^{-10}}} \ & =\sqrt{0.45 	imes 10^7} \ & =2.12 	imes 10^3 \mathrm{~V} / \mathrm{m} \ & =2.1 \mathrm{kV} / \mathrm{m} \end{aligned} \end{aligned} $$

Answer

$2.1 \mathrm{kV} / \mathrm{m}$

Answer

$1.4 \mathrm{kV} / \mathrm{m}$

Answer

$2 \mathrm{kV} / \mathrm{m}$

Answer

$0.5 \mathrm{kV} / \mathrm{m}$

EM waves

A laser beam of cross-sectional area 5 \mathrm{~mm}^2 is 30 mW . Find the magnitude of maximum electric field in this electromagnetic wave.

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