Practice question · Multiple choice
Why does the point-charge energy formula carry a factor of one half?
Hints
- Consider summing over every charge, each with the potential due to all the others.
- Charge i in j’s potential and charge j in i’s potential are the same interaction.
Show the answer
B. Each pair of charges would otherwise be counted twice
Why
Summing over all counts the interaction between each pair twice, once from each end. The corrects the double count; all the work is recoverable.
Practise Electrostatic Energy and Forces
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