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Homework Help: Earths potential?

  1. Sep 17, 2009 #1
    Earths potential???

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

    the problem reads as folloed
    Energy prospectors from a distant planet are inspecting the earth to decide if its electrical energy resources are worth stealing. Measurements reveal that earth's electric field extends upward for 800 m and has an average magnitude of 190 V/m. Estimate the electrical energy stored in the atmosphere.

    our TA gave us a hint and said
    You may treat the atmosphere as a flat slab with an area equal to the surface area of the earth.

    3. The attempt at a solution

    i tried to derive an equation. i keep getting the wrong answer so please check my math and see if im doing it wrong or just some calculation error.

    i started with
    U=1/2 Eo * E^2 Eo is 8.85e^-12
    then i went to
    U=EV substitued V=4/3pir^3 so got
    this is where i got stuck. i asked my TA and he said i was doing good so far.
    i played around with some stuff and got my U (potential) as follows
    but i get the wrong answer. any help would be great ;)
  2. jcsd
  3. Sep 18, 2009 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    Re: Earths potential???

    You're using the wrong volume, it's not a solid sphere.

    What is the surface area of the Earth?
    What is the volume of a slab that has that area, and the thickness given in the problem statement?
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