1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Distance of hearing a radio station

  1. Nov 16, 2008 #1
    1. The problem statement, all variables and given/known data
    A radio station is allowed to broadcast at an average power not to exceed 24 kW.
    If an electric field amplitude of 2.6×10−2 V/m is considered to be acceptable for receiving the radio transmission, estimate how many kilometers away you might be able to hear this station.

    2. Relevant equations

    P/A = e_0*c*E^2

    3. The attempt at a solution

    e_0*c*E^2/P = 1/pi r^2

    sqrt(24000/(8.85 *10^-12*3*10^8*pi)) = 65.2 km

  2. jcsd
  3. Nov 17, 2008 #2
    can anybody help?
  4. Nov 18, 2008 #3
    I just had this problem and this is how I solved it

    S=P/A where S=(.5)c(permittivity of free space)(E^2) - (this is the average value of S not an instantaneous value. Your equation for S was assuming the instantaneous value)

    then a little rearranging:

    (4)(pi)(r^2)=P/S - (4pir^2 is the surface area of a sphere, I think you were incorrectly using the area of a circle)

    you should be able to solve from here!
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook