7. Supplementary Questions

7.1 Take a moment to see and convince yourself of the analogies and differences between electrostatics and magnetostatics. 

7.2 Eight parallel wires cut the page perpendicularly at the points shown. A wire labelled with the integer k (k = 1, 2, ... , 8) bears the current 2k times \(I_0\) (i.e., \(I_k=\ 2k\ I_0\)). For those with k = 1 to 4, the current flows up out of the page; for the rest, the current flows down into the page. Evaluate \(\oint\vec{B}\cdot d\vec{s}\)along the closed path (see figure) in the direction indicated by the arrowhead. (Watch your signs!)