Two particles with charges +8e and -8e are initially very far apart (effectively an infinite distance apart). They are then fixed at positions that are 7.07 x 10-12 m apart. What is EPEfinal - EPEinitial, which is the change in the electric potential energy?

Answer 1

PE₁=k•q₁•q₂/r₁
r₁=∞ =>PE₁ =0
PE₂=k•q₁•q₂/r₂
r₂= 7.07•10⁻¹² m
ΔPE= PE₂ - PE₁=PE₂=
= 9•10⁹•8e(-8e)/ 7.07•10⁻¹²=
=-9•10⁹•(8•1.6•10⁻¹⁹)² /7.07•10⁻¹²=-
=2.1•10⁻¹⁵ J