- #1

darkrystal

- 4

- 0

## Homework Statement

In a xy-plane, we have a +q charge in A(0,h) and a -q charge in B(0,-h).

Let's take a field line passing through A, that has horizontal slope in A. Find the point C(m,0) where this field line intersects the X axis.

## Homework Equations

I think Gauss' law [tex]\epsilon_0 \oint \vec{E} \cdot d\vec{A}=q[/tex]

## The Attempt at a Solution

Let's take a surface passing through A and following the field lines till the y=0 plane. Apply the Gauss' law to it: the flux is only through the base of this surface, so that we should get

[tex]\displaystyle q=\epsilon_0 \int d\Phi = \epsilon_0 \int_0^m \frac{2khq}{(x^2+h^2)^{\frac32}} \cdot 2 \pi x dx[/tex]

where the second integral is the flux calculated for concentric rings around the origin. This equation, though, has no solutions for m, since it reduces to[tex]\displaystyle h(\frac{1}{h}-\frac{1}{\sqrt{h^2+m^2}})=1[/tex]

which is clearly impossible...Thank you all for your time, and please forgive my bad english and my even worse physics :)