Question

A point source of electromagnetic radiation has an average power output of $1500W$. The maximum value of electric field at a distance of $3m$ from this source in $V{m}^{-1}$ is

• A. 500
• B. 100
• C. $\frac{500}{3}$
• D. $\frac{250}{3}$

Answer 1

Answer: (B)

Average intensity of electromagnetic waves is
$I=\frac{P}{4\pi r^2}=\frac{1}{2}{\epsilon }_0{E}_0^{2}c$ or $E_0={\left[\frac{P}{2\pi r^2{\epsilon }_{0}c}\right]}^{1/2}$
Substituting the given values, we get
$E_0={\left[\frac{1500}{2\pi (3{)}^2\times \left[\left(1/4\pi \times 9\times 10^9\right)\right]\times 3\times 10^8}\right]}^{1/2}=100V{m}^{-1}$