Question

In bringing an electron towards another electron, the electrostatic potential energy of the system:

• A. decreases
• B. increases
• C. remains same
• D. becomes zero

Answer 1

Answer: (B)

The electron has negative charge.
When an electron is bringing 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 $r$ increases, potential energy $U$ increases.