Angle of electric field line heading to infinity

[bsvh]

Homework Statement

Charges 2q and -q are located on the x-axis at x=0 and x=a respectively.

(a) Find the point on the x-axis where the electric field is zero, and make a rough sketch of some field lines.

(b) You should find that some of the field lines that start on the 2q charge end up on the -q charge, while others head off to infinity. Consider the field lines that form the cutoff between these two cases. At what angle (with respect to the x axis) do these lines leave the 2q charge?

Homework Equations

E = 1/(4*pi*e0) q^2/r^2

The Attempt at a Solution

I found the solution for part (a) to be x = a(2 + sqrt(2)), but part (b) has me stumped and I'm not really sure how to approach it. Any pointers in the right direction would be greatly appreciated.

 

[user9345]

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