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Current Electricity

Question

Find the amplitude of the electric field in a parallel beam of light of intensity 8.0 W/m².

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Solution

Given,
Intensity of the parallel beam of light, I = 8.0 W/m²

Now,
Using the formula of the intensity of plane electromagnetic wave,

I = U_{av} c = \frac{1}{2} ε_{0} E_{0}^{2} c

\Rightarrow

E_{0} = {(\frac{2 I}{ε_{0} C})}^{1 / 2}

\Rightarrow

E_{0} = {[\frac{2 \times 8.0}{(8.85 \times 10^{- 12}) \times (3 \times 10^{8})}]}^{1 / 2}

i.e., E_o

= 77.6 {NC}^{- 1}