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Homework Help: Equipotentials around a charge Q

  1. May 19, 2010 #1
    Hi there,

    im having trouble finding the right equation for a problem ive got.

    I have a point charge with an equipotential of 40v at 0.4cm. I am suppossed to work out the value of the charge.

    Ive tried


    but it doesnt work and i think its because im not putting in a value for [tex]\epsilon[/tex]
    as i dont know what it is.

    cols anyone tell me if a, im using the right equation and b, hot to find or put in the value of [tex]\epsilon[/tex]

    many thanks
  2. jcsd
  3. May 19, 2010 #2


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    Gold Member

    You can use the value 1/4πε0 (the whole thing) = 9x109 N m2/C2. Don't forget to convert centimeters to meters.
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