Question
Net force, field lines:
If -q1 is negative, and -q2 is negative, why does this question here say that with resspect to q3, that q2 and q1 are pointing in opposite directions?
To me, q1 should be pointing in the positive direction as it is attracted to the positive charge of +q3 (so that F31 is positive), and q2 be pointing in the negative direction to be attracted to the charge of +q3 (so that F32 is negative)? Instead, the book writes it as the opposite. I know the book is right but I need to clarify why. Thanks
EXAMPLE 19-2 NET FORCE ge q,--5.4 pC is at the origin, and a charge=-22 C s on the x axis at x = 1.00 m. Find the net force acting on a A char charge 43 _ + 1.6 pC located at x-0.75 m PICTURE THE PROBLEM The physical situation is shown in our sketch, with each charge at its appropriate location. Notice that the forces exerted on charge q q3 by the charges qi and q2 are in opposite directions. We give the32. force on q3 due to qi the label F31, and the force on q3 due to 42 the o 91 F43 F32 42 31 0.75 m 1.00 m label F32 STRATEGY The net force on q3 is the vector sum of the forces due to 1 and q2. In particular, note that F31 points in the negative x direction (-x), whereas F32 points in the positive x direction (x). The magnitude of F31 is k al q3l/r2 with r = 0.75 m. Similarly, the mag nitude of Fa is kle I lq3l/r, with r-0.25 m SOLUTION 1. Find the force acting on 3 due to q. Since this force is in the negative x direction, as indicated in the sketch, we give it a negative sign --(8.99 × 109 N·m2/C2) 5.4 × 10-6 C)(1.6 × 10-6 (0.75 m) =-0.14 Ni 2l131 2. Find the force acting on qs due to q2. Since this force is in the positive x direction, as indicated 32
Explanation / Answer
The direction means that +ve charge will be attracted towards -ve charge
this direction does not show the magnitude of F31 or F32.