Q. 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) $9.37\ V/m$
Explanation
(a) $S_{av} = \frac{1}{2}\varepsilon_{0}cE_{0}^{2} = \frac{P}{4\pi R^{2}}$
$\Rightarrow E_{0} = \sqrt{\frac{P}{2\pi R^{2}\varepsilon_{0}C}}$
$= \sqrt{\frac{3}{2 \times 3.14 \times 100 \times 8.85 \times 10^{- 12} \times 3 \times 10^{8}}}$
$= 1.34V/m$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.