# Homework Help: How to sum charges?

1. Sep 15, 2010

### somasimple

1. The problem statement, all variables and given/known data
Attached figure.
3 charges : q1, q2 and q3 are on a plane (for simplification).
We want to compute the resulting charge at some point of the plane.
1/ Is it possible to sum (for computation) these charges to an arbitrary point A?
2/ or B?

2. Relevant equations
these ones ?
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/mulpoi.html

3. The attempt at a solution
I supposse I can't do it directly. I may use force or voltage or electric field?

#### Attached Files:

• ###### 3_charges_02.jpg
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2. Sep 15, 2010

### Office_Shredder

Staff Emeritus
I'm not sure what you're looking for. The charge at point A is zero, because there is no charge there.

3. Sep 15, 2010

### somasimple

I want to combine the 3 charges at point A or B.
I know that is possible to compute the voltage V=kq1/r1...
I'm interested in the result charge (virtual).

4. Sep 15, 2010

### Pengwuino

You can determine the potential or electric field at the point A, but you can't just reform the problem and just place a charge at an arbitrary point.

5. Sep 15, 2010

### somasimple

OK thanks but is it possible to compute the potential or EF at B (since distance becomes null)?

6. Sep 15, 2010

### Vyse007

Well, if B is a point inside the sphere, and if the said sphere is hollow, then you can find the electric field I think....of course, the field will be zero inside the shell if its conducting.

7. Sep 16, 2010

Thanks.