1. Problem1 statement, all variables and given/known data In the figure particle 1 of charge q1 = -8.13q and particle 2 of charge q2 = +3.63q are fixed to an x axis. As a multiple of distance L, at what coordinate on the axis is the net electric field of the particles zero? http://img201.imageshack.us/img201/4669/netfieldzeromy7.gif [Broken] 2. Relevant equations Electric Field = k|q| / r² The attempt at a solution Since it's a point between the two charged particles, let x = the distance between q1 and that point, so the distance between the point and q2 = L - x http://img157.imageshack.us/img157/990/netfieldzero2xj8.gif [Broken] The net electric field = 0, so -(Electric field due to q1) + (Electric field due to q2) = 0 E1 is negative because q1 is negative, E2 vice versa. -( k|-8.13q| / x² ) + ( k|3.63q| / (L - x)² ) = 0 Cancelling, etc gives: 4.5x² - 16.26Lx + 8.13L² = 0 quadratic formula gives: x = 0.6L or 3.01L I got it wrong, I'm also confused about the sign of the electric fields but the quadratic formula won't produce a real solution if both fields were negative or positive. 1. Problem2 statement, all variables and given/known data Charge is uniformly distributed around a ring of radius R = 2.41 cm and the resulting electric field is measured along the ring's central axis (perpendicular to the plane of the ring). At what distance from the ring's center is E maximum? 2. Relevant equations Electric Field of Ring = (kqx) / ( (x² + k²) ^ (3/2) ) The attempt at a solution I attempted to differentiate the equation with respect to x and put E' = 0, but I have two unknowns, x and q, the solution is a real number with no variables.