1. The problem statement, all variables and given/known data Consider 2 charges located in the x-y plane; q1 of magnitude 5 mC (millicoulombs) is located at the origin, and q2 of unknown magnitude is located at (x,y) = (0.1, 0) (in metres). The electric field E at position (0.03, 0.05) is found to be entirely in the +y direction (i.e. the x-component is zero). Determine the sign of charge q1 and the magnitude and sign of charge q2. 2. Relevant equations |q| = 5mC (microCoulombs) F= qE ; q= charge, E= electric Field E(r) = ƩEi(r) =1/(4*pi*ε°)*Ʃ(r-ri)*qi/(r-ri)3 3. The attempt at a solution E1(for one charge)= 1/(4*pi*ε°)*q1/r2 = 1/(4*pi*ε°)* (0.000005 C)/0.0015m E= 2.996*107 Then I went and did, E=1/(4*pi*ε°)[(q1/r2)+q2/(r-r2)2] rearrange for q2 and, q2= [E(4*pi*ε°)+(r2/q1)](r-r2)2 q2= -29.9997 C. (This seems way to high to be correct) So q1 is positive to make E in the + y direction.