Electric field due to dipole

czaitz

I'd like to check my thinking which is getting fuzzy:

Question: Two particles are fixed to an x axis: particle 1 of charge q1 = 2.91 x 10-8 C at x = 26.3 cm and particle 2 of charge q2 = -5.82q1 at x = 46.6 cm. At what coordinate on the x axis is the electric field produced by the particles equal to zero?

I am thinking: q1=2.91E-8C and q2=-1.694E-7C . I found the net electric field by using Coulomb's law, which is .0013 N/C. Now I need to find where the net E field is zero, and I thought that if I set E=0 I could find the r where E=0 but I can't seem to figure out how to do that. I can't just substitute E to find r ...I know it's not that hard but I'm experiencing a block...

Tomsk

Your net electric field shouldn't be a constant, it should be a function of x (or r, but you're only considering the one direction). It should be the sum of two electric fields, one from q1, one from q2. Then set it equal to zero and solve for x.

czaitz

Well, gosh, that makes sense! thanks!