# Work between two charges

1. Sep 14, 2009

### tooold

1. The problem statement, all variables and given/known data
I get depressed and frustrated with every physics problem. The more studying and reading I do, the worse my grade gets. Talk about diminishing returns. Anyway, charges q1=1.65x10^-5 C and q2=-5.65x10^-5 C are placed 0.6 m apart. How much work must be done by an outside agent to move these charges slowly and steadily until they are 0.355 m apart?

2. Relevant equations

V=k/r(q1+q2)
deltaV= -E*delta r
-W=-qE*delta r

3. The attempt at a solution
Attempt at the solution is more than likely wrong
Vinitial=k/0.6(q1+q2)
Vfinal=k/0.355(q1+q2)
deltaV= final-initial

deltaV=-W*(-q)
W=deltaV/q
I got a really huge number. I used q=1.65x10^-5 because the positive charge will move to the negative charge.

2. Sep 14, 2009

### kuruman

What does V = k/r(q1+q2) represent? It is the electrostatic potential due to what? Are the charges in the denominator as the equation seems to imply?

3. Sep 14, 2009

### tooold

V=k*(q1+q2)/r is the equation to find the electric potential.

4. Sep 14, 2009

### Fightfish

That unfortunately gives the electric potential at a point that is equidistant from both charges q1 and q2 at a distance of r, and will not aid you at all in this question.
You should consider how the overall potential energy of the system has changed.