1. The problem statement, all variables and given/known data This is Griffiths problem 5.4 NOTE: this is NOT for class, only for study :) I have the answer, but am unable to reproduce it! Problem: Given [tex] B = kz\hat x [/tex] where k is a constant, find the force on a square loop of size a lying in the yz plane and centered at the origin. 2. Relevant equations [tex]F = I\int dl \times B[/tex] is all we need. Clearly then, we get B = IaB. 3. The attempt at a solution Let's assume the current is counterclockwise. According to the answer I have, the force on the left side (towards the left) cancels the right side (towards the right). However, it appears to me that since z is analogous to x in this case, that as we move to the left or right the B-field increases and decreases. Is this not correct? If so, how can you say that the left cancels the right? Also, the answer claims that the force on the top points up, and the force on the bottom points up. This is true, only if the force on the bottom is negative, and the answer claims it is, however I don't see why this is so? Anyway, I'm clearly missing a few key points, so hope someone can help. Thanks!