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1. Nov 16, 2016

### Minescrushessouls

1. The problem statement, all variables and given/known data
A radio broadcast antenna is located at the top of a steep tall mountain. The antenna is broadcasting 104.3 FM (in Megahertz) with a power of 5.00 kilowatts.

What is the peak intensity of the signal at a receiving antenna located 25.0 km away?

2. Relevant equations
Honestly, I don't really know

Intensity=P/d^2

Peak Intensity=some vector/μ0

3. The attempt at a solution
So I tried doing 5000/(25000^2)

The power divided by the distance squared. The system told me my units were incorrect...so I guess I don't even know where to start on this

2. Nov 16, 2016

### Ugnius

You should use equation of Poynting vector

3. Nov 16, 2016

### Minescrushessouls

Ok so S=(ExB)/μ

But how would I find E and B from the information provided?

4. Nov 16, 2016

### Staff: Mentor

Intensity is measured in watts per square meter. Think of the radio antenna as putting out 5 kW in a spherical distribution. At some distance R from the transmitter, what's the size of the spherical "surface"?

5. Nov 16, 2016

### Minescrushessouls

So the area would be the area of a circle, or pi*r^2

So would that mean it would be W/(pi*r^2)?

6. Nov 16, 2016

### Staff: Mentor

No, the surface of a sphere is not a circle -- it's a spherical shell. What's the surface area of a spherical shell?

7. Nov 16, 2016

### Minescrushessouls

4*pi*r^2?

8. Nov 16, 2016

Yes.