# Homework Help: I'm trying to find electric potential.

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1. May 3, 2015

### +Jace090+

1. The problem statement, all variables and given/known data
There is a 4 cm by 3 cm rectangle with 2.0 nC charges at three corners. I'm trying to find the electric potential of the last corner in V.
2. Relevant equations
U=(kQq)/r I think
V=(kq)/r I think
3. The attempt at a solution
I found the U's between the know corners but i don't know where to go from there.

2. May 3, 2015

### Noctisdark

Hello Jace,
You add them up :) !

3. May 3, 2015

### +Jace090+

In this situation? I don't know if I adequately described it.

4. May 3, 2015

### +Jace090+

I found the U's of the sides with dimensions.

5. May 3, 2015

### Noctisdark

Aww, sorry for the mistake, There is no electric potential in the 4th corner, because there is no charge there, However you can calculate the voltage there (V) .

6. May 3, 2015

### +Jace090+

oh....... thank you.

7. May 3, 2015

### +Jace090+

Apparently there is because I typed in 0 and the program said I was wrong.

8. May 3, 2015

### +Jace090+

It wants the V for that point, so where would I go from having the U's of those adjacent to it?

9. May 3, 2015

### Noctisdark

Then, by electric potential he mean V (voltage), no charge means no electric potential energy (by intuition and the formula insists on that), however, calculate the voltage out there :)

Last edited: May 3, 2015
10. May 3, 2015

### +Jace090+

How would i go from U to V? What U would I use?

11. May 3, 2015

### Noctisdark

You can't go from U to V, cuz there'there's no charge out there, but one thing you can do is use V = kQ/R
[Edit: you can't because you'll be dividing by zero, moreover U = 0]

12. May 3, 2015

### +Jace090+

What Q and what R?Would i use the average?

13. May 3, 2015

### Noctisdark

R is the distance to the 4th coner, Q is the charge at each corner.
Calculate the potential due to each charge and sum them up !