Question

The amplitude of electric field in a parallel light beam of intensity $4W{m}^{-2}$ is

• A. $35.5N{C}^{-1}$
• B. $45.5N{C}^{-1}$
• C. $49.5N{C}^{-1}$
• D. $55.5N{C}^{-1}$

Answer 1

The correct option is D $55.5N{C}^{-1}$

Intensity , $I=\frac{1}{2}c{ϵ}_o{E}^2$ where $c$ and $E$ are the speed of light and amplitude of electric field respectively.

$4=\frac{1}{2}\times 3\times {10}^8\times 8.85\times {10}^{-12}\times |E{|}^2$

$⟹|E|=55.5N{C}^{-1}$