Sketch the electric field lines a long distance from the charge distributions shown in Figure 18.34 (a) and (b)
This is College Physics Answers with Shaun Dychko. We need to sketch the electric field a really long ways away from the charge distributions in figure [18.34]. So in part (a), we have a net charge of negative 2q which is—and it will seem like a point charge of negative 2q when we are really far away— and so it will be an uniformly distributed radial field with all the lines pointing towards this negative 2q charge. And they point towards the center here because that's the direction of force that would be applied on a positive test charge that's here; a positive test charge would be attracted to this negative 2q charge. In part (b), the net charge here is zero because this is positive q and then negative 1q which makes 0q so there's no field lines at all when you are really far away.