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Chapter 31: Q.20 (page 901)

A radio antenna broadcasts a1.0MHzradio wave with 25kWof power. Assume that the radiation is emitted uniformly in all directions.

a. What is the wave’s intensity 30 km from the antenna?

b. What is the electric field amplitude at this distance?

Short Answer

Expert verified

(a) Waves IntensityIo=2.2×10-6V/m

(b) Electric fieldEo=0.041V/m

Step by step solution

01

Introduction

Antennas are considerably more than simply radio-connected gadgets. They're the transducers that turn a transmitter's voltage into a radio signal. They also pick up radio signals in the air and convert them to a voltage that can be recovered in a receiver.

Given Values:

P=25×103W

d=30×103m

A=4πd2

02

Find Average Intensity

AvgIntensity Io

Io=P4πd2

Io=25×1034π30×1032

Io=2.2×10-6V/m

03

Find Electric field

Electric field Ep:

Eo=2Iavgc·εo1/2

Eo=2×2.2×10-63×108×8.85×10-121/2

Eo=0.041V/m

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