Physics

Problem

For two identical positive point charges +q separated by a distance r in vacuum, what is the sign of their electric potential energy U? a)

U

is negative, because like charges repel and the system tends toward lower energy at larger separations. b)

U

is zero, because the forces on the two charges are equal in magnitude and opposite in direction. c)

U

is positive, because

U = kq^2/r

and

q^2

is positive. d)

U

can be positive or negative depending on the distance

r

between the charges.