Question

A lamp emits monochromatic green light uniformly in all directions. The lamp is $3$% efficient in coverting 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. $1.34V/m$
• B. $2.68V/m$
• C. $5.36V/m$
• D. $9.37V/m$

Answer 1

The correct option is A $1.34V/m$

$S_{av}=\frac{1}{2}{\epsilon }_{0}c{E}_0^2=\frac{P}{4\pi R^2}$
$\Rightarrow E_0=\sqrt{\frac{P}{2\pi R^2{\epsilon }_{0}C}}$
$=\sqrt{\frac{3}{2\times 3.14\times 100\times 8.85\times {10}^{-12}\times 3\times {10}^8}}$
$=1.34V/m$