Question

Question 17 (1 point) Satellites use breams of EM waves to communicate with devices on Earth. Suppose a particular satellite has a power of 18 kW and sends a focused cone of EM waves toward Earth 4.9x10^2 km away. When the focused beam reaches the Earth, its circular diameter is about 1.3 km. What is the peak electric field strength in this focused beam? Onone of these 29 V/m 10. V/m O 49 V/m 18 V/m

Answer 1

given

power p = 18000 W

radius r = 1300/2 = 650 m

from hte realtion

intensity I = p/A

I = 18000/3.14*650^2 = 0.0136 W/m^2

peak electric field E0 = (2*I/c* $\varepsilon 0$ )^1/2

E0 = (2*0.0136/3*10^8*8.85*10^-12)^1/2 = 3.2 V/m

answer is none of the above