Posted by **Kevin** on Thursday, September 21, 2006 at 10:43pm.

Four identical charges (+1.6 ìC each) are brought from infinity and fixed to a straight line. Each charge is 0.36 m from the next. Determine the electric potential energy of this group.

i placed the charges as follow

q1 q2 q 3 q4

and used q1 as the starting point so EPE = 0

then i used the equation V = Kq/r and multiple the V by (1.6 micro columb) to get the EPE. I did that for q2 q3 q4 and changing r as i get closer to q4. Then i added all the EPE together but i am missing something.

EPE of q1 = 0

EPE of q2

(q1)(k)/(.36m) = V

EPE2 = (V)(1.6 micro columb)

EPE of q3

(q)(k)/(.36m) + (q)(k)/(.36m x 2) = V

EPE3 = (V)(1.6 micro columb)

EPE of q4

(q)(k)/(.36m) + (q)(k)/(.36m x 2) + (q)(k)/(.36m x 4) = V

EPE4 = (V)(1.6 micro columb)

Add EPE (1 + 2 + 3 + 4) = Total EPE of the group

but i am doing something wrong, can someone help thanks

EPE of q4:

(q)k[1/(0.36 m)+ 1/(2x0.36 m) + 1/(3x0.36 m)]