Does Voltage at Point P Reflect Net Attraction Despite Equal Charges?

[mm2424]

Homework Statement

What is the net electrical potential at point P due to the four particles if V = 0 at infinity, q = 5 fC and d = 4 cm? The image for this problem can be seen at http://www.webassign.net/hrw/hrw7_24-33.gif

Homework Equations

Potential = 1/(4εpi) * q/r

The Attempt at a Solution

I was able to answer this question, and the answer agrees with the answer key. However, it's left me a bit confused. Potential is a scalar, correct? How does one interpret the meaning of the voltage for point P if, say, only the two +q charges were present. Do the voltages cancel out, or do they add up? I ask because, when I answered this problem, I just blindly added up all the potentials at point P from each charge, regardless of the charges' location. I added the pluses, subtracted the minuses, and got the right answer (which ends up being .54 mV). But does that mean that there is a net positive attraction for the particle? I don't see how that makes sense, since the electrical fields from the positive charges should cancel, no? I imagine I'm looking at this the wrong way...any help would be greatly appreciated!

 

[gneill]

I was able to answer this question, and the answer agrees with the answer key. However, it's left me a bit confused. Potential is a scalar, correct? How does one interpret the meaning of the voltage for point P if, say, only the two +q charges were present. Do the voltages cancel out, or do they add up?

The potentials add. Potential obeys the superposition rule, so you can treat one sourtce at a time and sum the contributions of each.

 

[mm2424]

So if you had a point that was equidistant between two equal positive charges q, the voltage would be positive and not 0?

 

[gneill]

So if you had a point that was equidistant between two equal positive charges q, the voltage would be positive and not 0?

Yes. The potential (a scalar) would be the sum of the contributions from each charge, both of which are positive.