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 100W of power. The amplitude of the electric field associated with the electromagnetic radiation at a distance of 10m from the lamp will be

• A. 1.34 V/m
• B. 2.68 V/m
• C. 5.36 V/m
• D. 9.37 V/m

Answer 1

The correct option is A

1.34 V/m

$S_{av}=\frac{1}{2}{ϵ}_{0}c{E}_0^2=\frac{P}{4\pi R^2}$

$\Rightarrow E_0=\sqrt{\frac{P}{2\pi R^2{ϵ}_{0}C}}$

$=\sqrt{\frac{3}{2\times 3.14\times 100\times 8.85\times {10}^{-12}\times 3\times {10}^8}}$
=1.34 V/m