Homework Help: Intensity From a Point Source

1. Nov 11, 2007

Ryo124

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

A point-like source of electromagnetic waves radiates power uniformly in all directions at a single frequency.

At a distance of 5.6 km from the source, a detector measures the intensity (energy flux density) of the wave to be 35.1 μW/m2 (microwatts per square meter).

a)Calculate the amplitude of the magnetic field oscillations of the wave at the detector.

b)What is the total power radiated by the source?

Hint: The intensity (power/area) is c ε0 E0^2/2 where E0 is the amplitude of oscillation of the electric field in the wave. Then the magnetic field is B0=E0/c.

2. Relevant equations

The relevant equations are given in the "Hint" of the problem. And I used 8.85E-12 for epsilon.

3. The attempt at a solution

I got 0.163 T for the amplitude, but it is wrong. I got 1.425E-12 W for the power, but it is also wrong. Help please.

2. Nov 12, 2007

mgb_phys

The power is easy, what is the surface area of a sphere wih radius = 5600m,
If the intensity is 35.1E-6w/m^2 what is the total power for this area, hint the units should come out as watts!

3. Nov 12, 2007

Ryo124

Alright, I got a). I cannot figure out b) though.

4. Nov 12, 2007

Ryo124

Thanks mgb. I got both parts