A positive point charge q is placed at x=a and a negative point charge -q is placed at x=-a. a: find the magnitude of the electric field and the direction at x= 0. b: derive an expression for the electric field at points on the x-axis. use results to graph the x-component of the electric field as a function of x, for values x between -4a and +4a. I would get the first part by using e=1/4pi(e0) * modulus q / r^2 so in this case i would get 2q/4pi(e0)a^2 .. right? now how do i got about doing question b... don't even know where to start.