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Coulomb's law and two spheres

  1. Aug 31, 2010 #1
    I thought this would be a basic physics problem, but I'm not getting the right answer, here's the problem:

    There are two identical small metal spheres with charges 27.5 μC and −19.119 μC. The distance between them is 8 cm. The spheres are placed in contact then set at their original
    distance. Calculate the magnitude of the force between the two spheres at the final position. The Coulomb constant is 8.98755 × 109 N · m^2/C2 .
    Answer in units of N.

    I used the formula, F=K*((q1*q2)/r^2)). I converted the charges using the 10^-6 conversion.

    So, F=(8.98755*10^9)*(27.5*10^-6 * 19.119*10^-6) all over 0.08^2 and I got 738.3448 N.

    The answer is incorrect according to the online service my class uses, what did I do wrong?
  2. jcsd
  3. Aug 31, 2010 #2
    Did you take into account that they were temporarily placed in contact?
  4. Sep 2, 2010 #3
    How would I do that?
  5. Sep 2, 2010 #4


    Staff: Mentor

    The spheres are metal and therefore conductive. What happens to the charges when two charged conductive materials come in contact?
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