A red LED emits light at 0.1 watt uniformly around it. The amplitude of the electric field of the light at a distance of 1 m from the diode is:

Engineering

Physics

Electromagnetic Waves

Question

2.45 V/m

1.73 V/m

7.75 V/m

5.48 V/m

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$I = \frac{1}{2} ε_{0} E^{2} C = \frac{P}{A}$

$\frac{0 .1}{4 π {(1)}^{2}} = \frac{1}{2} ε_{0} E^{2} C$

$E = \sqrt{\frac{0 .1 \times 2}{4 π 8 .35 \times 10^{- 12} \times 3 \times 10^{8}}} = 2 .45 v / m$