Potential Due to a Group of Point Charges

[queenspublic]

Homework Statement

Homework Equations

The Attempt at a Solution

First time: I got -1.468e-19 which is wrong.
Second time: I got -6.407e-19 which is wrong.

q₁ = 3.337e-19 ?

 

[lanedance]

can't quite follow your working, here's how I would look at it:

q₁ is located at distance d from the origin

The graph gives the potential at the origin, as q₂ charge is moved a distance x away from the origin.

Unknowns:
q₁
q₂

when the 2nd charge is at infinity, the potential at the origin, V, will be only due to q₁, use this to calculate q₁ in terms of V & d.

Then pick a suitable point from you graph, the zero crossing, x = 8, seems the easiest to me,

you know q₁ is d from the origin & q₂ is x from the origin, and the net potential is zero, us these facts to calculate q₂.