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Earth's Electric Field

  1. May 27, 2004 #1
    I am having trouble doing this question.

    Measurements indicate there is an electric field surrounding the earth. Its magnitude is about 100 N/C at the earth's surface and points to the centre of the earth. What is the magnitude of the electric charge on the earth? Is it positive or negative?
    (Hint: The electric field caused by a uniformly charged sphere is the same as if the entire charge were concentrated at its centre)
     
  2. jcsd
  3. May 27, 2004 #2

    chroot

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    Look in your book and find out which direction field lines point. Do they leave positive charges and end on negative charges? Or vice versa?

    - Warren
     
  4. May 28, 2004 #3
    but how do I find the magnitude of the electric charge on earth?
    I don't have enought information
     
  5. May 28, 2004 #4

    chroot

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    Use the definition of the field due to a point charge. Pretend that all of the earth's charge is concentrated at a point at the center of the earth. The earth's radius is 6,378.1 kilometers.

    [tex]E = \frac{1}{4 \pi \epsilon_0} \frac{q}{r^2}[/tex]

    - Warren
     
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