Question 24: EM waves

Question

A lamp emits monochromatic green light uniformly in all directions. The lamp is 3% efficient in converting electrical power to electromagnetic waves and consumes 100 W of power. The amplitude of the electric field associated with the electromagnetic radiation at a distance of 5 m from the lamp will be nearly :

Accepted Answer

Since $\quad U_E 	imes c=I=$ Intensity
$$
\begin{aligned}
& \frac{1}{2} \varepsilon_0 E^2 	imes c=I=\frac{P}{4 \pi R^2}=\frac{3 / 100 	imes P}{4 \pi R^2} \\
E & =\sqrt{\frac{6 P}{\varepsilon_0 	imes c 	imes 100 	imes 4 \pi R^2}} \\
& =\sqrt{\frac{6 	imes 100}{8.85 	imes 10^{-12} 	imes 3 	imes 10^8 	imes 100 	imes 4 \pi 	imes(5)^2}} \\
& =2.68 \mathrm{~V} / \mathrm{m}
\end{aligned}
$$

Answer

1.34 V/m

Answer

2.68 V/m

Answer

4.02 V/m

Answer

5.36 V/m

EM waves

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