Question

In lecture #2, time 11:20 Proff. Lewin wants us to calculate when will the field be zero on the line passing through two charges +3 and -1 respectively.
I calculated and the answer was that point is at distance d(3+3^.5)/2 OR d(3-3^.5)/2 from the +3 charge, and d is the distance between the two charges. I got two results cause I was solving a quadratic equation, but the second result is clearly wrong because it places the zero field point between the two charges. Can anyone check my solution?

Answer 1

I did a quick check, your first answer is that the point is 1,37d apart from (-1) charge and 2,37d apart from (+3) charge, so if E is zero there, by superposition, 3/(2.37^2)=1/(1.37^2) which is quite the case.
So, it seems to be ok!

Answer 2

Thanks