Question

A spherically spreading EM wave comes from an 1800-W source. At a distance of 5.0 m, what is the intensity, and what is the rms value of the electric field?

Answer 1

Answer:

The intensity of the EM wave is 5.729 W/m²

The rms value of the electric field is 46.452 V/m

Explanation:

Given;

power of the electromagnetic wave, P = 1800 W

The intensity of light is given by;

I = P / A

Where;

A is the surface area of the sphere = 4πr²

A is the surface area of the sphere = 4π(5)²

A is the surface area of the sphere = 314.2 m²

The intensity is calculated as;

I = P / A

I = (1800) / (314.2)

I = 5.729 W/m²

The rms value of the electric field is given by;

$E_{rms} = \sqrt{\frac{I}{c \epsilon _o}}\\\\E_{rms} = \sqrt{\frac{5.729}{(3*10^8)( 8.85*10^{-12})}}\\\\E_{rms} = 46.452 \ V/m$