Posted by Allee on .
Four identical charges (+4.0 uC each) are brought from infinity and fixed to a straight line. The charges are located 0.33m apart. Determine the electric potential energy of this group.

physics 
drwls,
Add up the work required to bring the charges into their places, one at a time.
Let the charge separation for adjacent charges be a = 0.33 m
The Coulomb constant is k, and each charge is Q = 4*10^6 C
First charge: work = 0
Second charge: work = kQ/a
Third charge: work = kQ/a + kQ/(2a)
Fourth charge: work = kQ/a + kQ/(2a) + kQ/(3a)
Add them for the total potential energy
PE = (13/3) kQ/a 
physics 
joe,
PE=(13/3)k(Q^2)/a

physics 
joe,
45