Potential
energy of two charges q1, q2 at r1, r2 is given by
1
2
0
12
1
4
q q
U
r
ε
=
π
where r12 is distance between q1 and q2 7 The potential energy of a charge q in an external potential V(r) is qV(r) The potential energy of a dipole moment p in a uniform electric field E
is  –p