Question

Find the amplitude of the electric field in a parallel beam of light of intensity $2.0{\text{Wm}}^{-2}$.

• A. $15.5\text{N/C}$
• B. $38.8\text{N/C}$
• C. $40.3\text{N/C}$
• D. $53.6\text{N/C}$

Answer 1

The correct option is B $38.8\text{N/C}$

Given:-
$I=2{\text{W/m}}^2$

The intensity of a plane electromagnetic wave is given by

$I=\frac{1}{2}{\epsilon }_0{E}_0^{2}c$

$\Rightarrow E_0^2=\frac{2I}{{\epsilon }_{0}c}$

or, $E_0=\sqrt{\frac{2I}{{\epsilon }_{0}c}}$

$E_0=\sqrt{\frac{2\times 2}{8.85\times {10}^{-12}\times 3\times {10}^8}}$

$E_0=38.8\text{N/C}$

Hence, option $\left(B\right)$ is correct.