- #1

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## Homework Statement

3 charges are spread as drawn. the first question was what's the field at point B, but that i solved.

The second question was what is the work needed to bring the charge q that's at point A to point B.

## Homework Equations

The potential at a point: ##V=k\frac{q}{r}##

The work: ##W=q\cdot \Delta V##

## The Attempt at a Solution

I don't think i have to take into consideration the charge that i should move. it contributes to the field at B but it changes. and i am not sure if i have to take him in consideration also at the start point A because r=0 and V→∞ so:

$$V_A=kq\left(\frac{1}{3}+\frac{4}{4}\right)=\frac{4}{3}kq$$

$$V_B=kq\left(\frac{1}{\sqrt{13}}+\frac{4}{\sqrt{20}}\right)$$

$$W=kq^2\left(\frac{1}{\sqrt{13}}+\frac{4}{\sqrt{20}}-\frac{4}{3}\right)$$

I think it should be:

$$W=kq^2\frac{1}{6}$$