A radio tower is broadcasting a signal with an average power of 50 kW. The energ
ID: 2103237 • Letter: A
Question
A radio tower is broadcasting a signal with an average power of 50 kW. The energy is radiated uniformly in all the directions. You are driving in a car, radially away from the radio tower with a receiver which can receive radio signals with intensity 10^-7 W/m^2 and higher.
A. Wil you be able to receive the radio signal at a distance of 100 m?
B. Will you be able to receive the radio signal at a distance of 100 km?
C. What is the amplitude of the electric field of the signal at a distance of 100 m?
D. At what distance is the magnitude of the electric field of the signal reduced to 1/1000 of its value found at 100 m?
Explanation / Answer
a) Divide the number of Watts by the number of square meters (area of a sphere of 100 m radius). That gives you the Watts per square meter. See if it's more than 10^-7 W/m^2.
b) Divide the number of Watts by the number of square meters. See if it's more than 10^-7 W/m^2.
c) Amplitude of E is the square root of intensity.
d) Intensity is proportional to 1/r^2. Electric field is the square root of intensity