# Homework Help: Invisible charge?

1. Jun 15, 2013

### somasimple

"Invisible" charge?

HI all,

1. The problem statement, all variables and given/known data
See attached picture. q1 is at equal distance from A or B.
k = coulomb's constant

2. Relevant equations

VA = (k q1 / r)
VB = (k q1 / r)

3. The attempt at a solution

VAB = VA - VB = 0 V

It seems that the charge becomes invisible in that case, right?

#### Attached Files:

• ###### ddp_04.png
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2. Jun 15, 2013

### Staff: Mentor

The charge is not invisible.

We have (roughly) the same gravitational potential everywhere on the surface of earth. Is earth invisible? Do you float freely in space?

3. Jun 16, 2013

### somasimple

That's right but its effect on voltage difference is the same as if there was no charge.

4. Jun 16, 2013

### voko

Any charge configuration admits equipotential surfaces. The potential difference between any two points on such a surface is zero. Which does not mean there is no charge.