# Homework Help: Electrical potential energy

1. Feb 16, 2009

### synergix

1. The problem statement, all variables and given/known data
Compute the electric potential energy for the charge configuration shown below.

http://webct6.nic.bc.ca/webct/RelativeResourceManager/Template/CourseMaterials/CourseContent_2007FA/Assignments/PHY060W_Assignment_07_files/image025.jpg [Broken]

2. Relevant equations

TPE=PE11+PE12+(PE13+PE23)

3. The attempt at a solution

TPE=PE11+PE12+(PE13+PE23)
| TPE= 0J+[(q1KQ2)/r2] + [(q1KQ3)/r1 + (q2KQ3)/r3]
|
q1=-3.0 microcoloumb
q2=2.0microcoloumb
q3=5.0microcoloumb

| where q1 is charge 1, q2 and Q2 are charge 2, Q3 is charge 3, r1 is the distance between q1 and Q3, r2 is the distance between charge 1 and 2, r3 is the distance between q2 and Q3.

I have chosen charge one to base my calculations off. I had problems before with this question and I was instructed to find charge one due to charge one + PE on charge one due to charge 2 + (PE on charge 1 due to charge 3 + PE on charge 2 due to charge 3) I am not sure why I need to calculate the potential energy on charge 2 due to charge 3. So I need to know if my equation is correct and also why I need to calculate the potential energy of charge 2 due to charge 3 when I am using charge one to base my calculations off of?

Last edited by a moderator: May 4, 2017
2. Feb 16, 2009

### Redbelly98

Staff Emeritus
Without seeing a figure showing the charges, I will say that the total potential energy is the potential due to each pair of charges.

Your equation looks correct. Not sure why you bothered with the "PE11" term, since it's just 0, or why you chose to use different symbols (q2 and Q2) for one of the charges. But it is correct. If the figure shows what r1, r2, and r3 are, you can go ahead and plug in the numbers.

3. Feb 16, 2009

### LowlyPion

4. Feb 16, 2009

### synergix

Ok thanks I used the small q to indicate that it was the charge being acted upon by the big Q. I believe that is what is happening. its just personal preference I suppose albeit kinda pointless and possibly confusing if you don't know why I am doing that.

5. Feb 16, 2009

### synergix

sorry for the double post