# Determining the amplitude of an electric field from a broadcast satellite

1. Dec 2, 2011

### kmendonc

1. The problem statement, all variables and given/known data

A satellite in geostationary orbit is used to transmit data via electromagnetic radiation. The satellite is at a height of 35,000 km above the surface of the earth, and we assume it has an isotropic power output of 1 kW (although, in practice, satellite antennas transmit signals that are less powerful but more directional).

Reception devices pick up the variation in the electric field vector of the electromagnetic wave sent out by the satellite. Given the satellite specifications listed in the problem introduction, what is the amplitude of the electric field vector of the satellite broadcast as measured at the surface of the earth? Use for the permittivity of space ε = 8.85x10^-12 C/(Vm) and c = 3x10^8 for the speed of light

2. Relevant equations

Intensity = Power/Area
E(sub_0) = root(2μ0cI)

3. The attempt at a solution

I = 1x10^3 W / (4∏(3.5x10^4)^2

I don't know where to go once I've figured the intensity....Please and thanks!

2. Dec 2, 2011

### Staff: Mentor

If your Relevant Equations are to be believed, then

$E_o = \sqrt{2 \mu_o c \; I}$

That would yield a result in Volts/meter.