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Why it's (1/2)? [Electric Potential Energy]

  1. Sep 12, 2015 #1
    upload_2015-9-12_15-30-47.png
    My question is, why it's 1/2 [qiVi]? Shouldn't it just be qiVi?

    Thank you ...
     
  2. jcsd
  3. Sep 12, 2015 #2

    robphy

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    You want to count "pairs"...
    That is, if you include both [itex]\frac{q_1q_2}{r_{12}}[/itex] and [itex]\frac{q_2q_1}{r_{21}}[/itex], you are counting the same "pair" twice.
     
  4. Sep 12, 2015 #3
    Oh I see,
     
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