Question

Derive expression for Potential Energy.

Answer 1

Potential energy of one two particle pair
is given as

U = kq1q2/r
where,
k = 1/4π*epsilon(0)

Now in three particle case we have three pairs of typical electrically active systems

So,
Total potential energy = k*q1q2/r + kq2q3/r + kq1q3/r

Answer 2

$\textbf{Answer is in attachment!}$