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Radio Broadcast Antenna Peak Intensity

  1. Nov 16, 2016 #1
    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. jcsd
  3. Nov 16, 2016 #2
    You should use equation of Poynting vector
     
  4. Nov 16, 2016 #3
    Ok so S=(ExB)/μ

    But how would I find E and B from the information provided?
     
  5. Nov 16, 2016 #4

    gneill

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    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"?
     
  6. Nov 16, 2016 #5
    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)?
     
  7. Nov 16, 2016 #6

    gneill

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    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?
     
  8. Nov 16, 2016 #7
    4*pi*r^2?
     
  9. Nov 16, 2016 #8

    gneill

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    Staff: Mentor

    Yes.
     
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