Two protons are brought closer together. The electrostatic potential energy of the pair

  • A. increases, because work must be done against their repulsion
  • B. decreases
  • C. stays constant
  • D. becomes negative

Explanation

Like charges repel, so pushing them together requires work and that work is stored as potential energy, which is why the system flies apart if released. For unlike charges the energy is negative and becomes more negative as they approach, since the force does the work instead. The sign convention takes zero energy to be infinite separation.

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