Question

A $27$mW laser beam has a cross-sectional area of $10$ $m{m}^2$. The magnitude of the maximum electric field in this electromagnetic wave is given by?[Given permittivity of space ${\in }_0=9\times {10}^{-12}$SI units, Speed of light $c=3\times {10}^8$ m/s]

• A. $1$ kV/m
• B. $2$ kV/m
• C. $1.4$ kV/m
• D. $0.7$ kV/m

Answer 1

The correct option is C $1.4$ kV/m

Intensity of EM wave is given by

$I=\frac{Power}{Area}=\frac{1}{2}{\epsilon }_0{E}_0^{2}C$

$\frac{27\times {10}^{-3}}{10\times {10}^{-6}}=\frac{1}{2}\times 9\times {10}^{-12}\times E^2\times 3\times {10}^8$

$E=\sqrt{2}\times {10}^3$ kV/m

$=1.4$ kv/m.