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: Electric Potential/Energy question

  1. Nov 23, 2003 #1
    Here's the question: "How much work must be done to bring three electrons from a great distance apart to within 1.0 x 10^-10 m from each other?"

    Here's what I did :

    .(work to bring one to another)

    Work = PE + KE
    = PE + 0
    =q(V final - V initial) ; V initial = 0
    =qV final
    = (1.6 x 10^-19)((9 x 10^9 x 1.6 x 10^-19)/(1.0 x 10^-10))
    = 2.3 x 10^-18 J

    .(work to bring the other one)

    Work = q(KQ/r)
    = (1.6 x 10^-19)((9 x 10^9 x 1.6 x 10^-19)/(2 x 1.0 x 10^-10))
    = 1.2 x 10^-18 J

    . I then add them together to get the total work done

    (2.3 x 10^-18 J) + (1.2 x 10^-18 J)
    = 3.4 x 10^-18 J

    Now, is that right? Feel free to correct me.
  2. jcsd
  3. Nov 23, 2003 #2
    I may be interpreting the question differently from you. I interpret it to mean that the three electrons are brought into the configuration of an equilateral triangle, with each edge of the triangle r=1 angstrom in length.

    If so, then you can compute the final potential energy of one of the pairs of charges with ke2/r, and the final total potential energy of the three charges is three times that (energy from three pairs of charges).
  4. Nov 23, 2003 #3
    I see. I'm visualizing the question as three electrons coming together in a line. Bleh, the book didn't provide a diagram. However, I think you're right. Thanks for guiding me in the right direction.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook