Question

Which of the following describes the potential energy, U, between an electron and proton separated by a distance r. Keep in mind that k = 1/(4 x pi x epsilon_o) and the charge on an electron is -e and the charge on a proton is +e.

1) U=-ke^2/r

2) U=+ke^2/r

3) U=-ke^2/r^2

4) U=+ke^2/r^2

Answer 1

In Electrostats we study about the potential energy of charge system.

for binary charge system value of potential energy is   
and in the above formula charge is put along with sign.

so, for a proton and electron charge system:
charge of proton = e
and charge of electron = -e

so, potential energy will be:

so the answer is option 1)