Question

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 5.05 x 10^-12 m apart. What is EPE_final - EPE_initial, which is the change in the electric potential energy?

Answer 1

electric potential energy is given by:

EPE = k*q1*q2/r

So,

EPE_final - EPE_initial = k*q1*q2/r_f - k*q1*q2/r_i = k*q1*q2*(1/r_f - 1/r_i)

r_i =

r_f = final separation between both charges = 5.05*10^-12 m

q1 = +8e, q2 = -8e

Using given values:

EPE_final - EPE_initial = 9*10^9*8e*(-8e)*(1/(5.05*10^-12) - 1/)

EPE_final - EPE_initial = -9*10^9*64*(1.6*10^-19)*(1/(5.05*10^-12) - 0)

EPE_final - EPE_initial = -2.92*10^-15 J

Let me know if you've any query.