First slide

Intensity of electromagnetic wave

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

Moderate

A

1.34 V/m
B

2.68 V/m
C

5.36 V/m
D

9.37 V/m

Solution

$\begin{array}{rcl} I & = & \frac{P}{4 {πr}^{2}}, P = 3 % of 100 W = 3 W \\ \frac{P}{4 {πr}^{2}} & = & \frac{1}{2} \in_{0} {E_{0}}^{2} C; \\ \frac{P}{r^{2}} & = & \frac{1}{2} (4 π \in_{0}) {E_{0}}^{2} C \\ \frac{3}{100} & = & \frac{1}{2} \frac{1}{9 x 10^{9}} {E_{0}}^{2} x 3 x 10^{8} \\ {E_{0}}^{2} & = & 1.8; \\ E_{0} & = & \sqrt{1.8} = 1.34 {Vm}^{- 1} \end{array}$

Get Instant Solutions

When in doubt download our app. Now available Google Play Store- Doubts App

Recieve an sms with download link

Doubts App

OR

SCAN ME

Doubts App

Doubts App