A lamp emits monochromatic green light uniformly in all directions. The lamp is 3% efficient in converting electrical power to electromagnetic waves and consumes 100W of power. The amplitude of the electric field associated with the electromagnetic radiation at a distance of 10m from the lamp will be:
Answer & explanation
Correct answer: option 1
$S_{\mathrm{av}}=\frac{\mathrm{P}}{4 \pi \mathrm{R}^2}=\frac{1}{2} \varepsilon_0 \mathrm{cE}_0^2$
∴ $E_0= \sqrt{\frac{P}{2 \pi R^2 \varepsilon_0 c}}$
$=\sqrt{\frac{3}{2 \times 3.14 \times 100 \times 8.85 \times 10^{-12} \times 3 \times 10^8}}$
= 1.34 V/m