Physics - Modern Physics Question with Solution | TestHub

The electron has negative charge. When an electron is approaching towards another electron, then due to same negative charge repulsive force is produced between them. So, to bring them closer a work is done against this repulsive force. This work is stored in the form of electrostatic potential energy. Thus, electrostatic potential energy of system increases. Alternative Electrostatic potential energy of system of two electrons $$U=\frac{1}{4\pi {\epsilon }_0}\frac{(-e)(-e)}{r}=\frac{1}{4\pi {\epsilon }_0}\frac{e^2}{r}$$ Thus, as $r$ decreases, potential energy $U$ increases.