A parallel-plate capacitor with circular plates of radius \(r\) is charging with constant current \(I\). At some instant, \(B=\) \(1.6 \times 10^{-8} \mathrm{~T}\) at a position \(7.0 \mathrm{~mm}\) from the center of a long wire leading to the capacitor.

(a) Calculate the current magnitude at that instant.

(b) Draw the current in one plate to show why you get the same value of \(B\) no matter where you place the surface bounded by your Ampèrian path. Draw the lengths of your current arrows to scale to show how the current magnitude does or does not change at various positions in the plate.