Question

14 question is a doubt
Q.14. 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 :-
(1) 5.48 V/m
(2) 7.75 V/m
(3) 1.73 V/m
(4) 2.45 V/m

Answer 1

Dear Student,
$$\begin{gathered} I=\frac{Power}{4{\mathrm{\pi r}}^2} \\ also,I=\frac{1}{2}c{\in }_0{E}^2 \\ fromaboveequations \\ E=\sqrt{\frac{P}{4{\mathrm{\pi r}}^2}\times \frac{2}{c{\in }_0}} \\ =\sqrt{\frac{0.1}{1^2}\times \frac{2\times 9\times {10}^9}{3\times {10}^8}} \\ =\sqrt{6}=2.5V/m \end{gathered}$$
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