# Voltage and point charge

1. Aug 19, 2008

### rissa_rue13

1. The problem statement, all variables and given/known data
There is an equilateral triangle with one point charge at each vertex. The point charges have charges of +Q, +2Q, and -4Q. The length of one side of the triangle is L. Determine an expression in simplest form for the voltage at a point halfway between the +Q and +2Q point charges.

2. Relevant equations
V=kQ/r
Vnet=V1+V2+V3

3. The attempt at a solution
Going off of Vnet=V1+V2+V3:
Vnet= (kQ/r) + (k2Q/r) - (k4Q/r)
I think once substituting the values for L in place of r, you get:
Vnet= (kQ/(L/2)) + (k2Q/(L/2)) - (k4Q/Lcos30)
Am I heading in the right direction?

2. Aug 19, 2008

### Redbelly98

Staff Emeritus
Yes, that looks good.

3. Aug 19, 2008

### rissa_rue13

I think I made a mistake, I think it should be:
Vnet= (kQ/(L/2)) + (k2Q/(L/2)) - (k4Q/(L/cos 30))

This can then be simplified:
Vnet=kQ[(2/L)+(4/L)-(4cos30/L)]

Am I on the right track?

4. Aug 19, 2008

### LowlyPion

The distance from the far vertex is L(cos 30). I think you were right the first time.