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 :
Show Hint
- 5.48 V/m
- 7.75 V/m
- 1.73 V/m
- 2.45 V/m
The Correct Option is D
Solution and Explanation
For an EM wave, \(I = \frac12\varepsilon_0 c E_0^2\), so \(E_0 = \sqrt{\frac{2I}{\varepsilon_0 c}}\).
\(\varepsilon_0 c = 8.85\times10^{-12}\times 3\times10^{8} = 2.655\times10^{-3}\).
\(E_0^2 = \frac{2\times 7.96\times10^{-3}}{2.655\times10^{-3}} \approx 6.0 \Rightarrow E_0 \approx 2.45\ \mathrm{V/m}\).
Answer: (4) 2.45 V/m
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