1. The problem statement, all variables and given/known data The diagram illustrates a Helmholtz coil, consisting of two identical circular coils of wire, each one having N loops and carrying the same current I. The radius of each coil is R, and the two coils are R meters apart. (a) What are the direction and strength of the magnetic field at the point Z, midway between the two coils? (b) Express B as a function of the variable z, taking the origin for z to be at the center of the left-hand coil and the positive z direction to be to the left. (c) Find the first and second derivatives of the magnetic field strength B with respect to z, dB/dz and d 2B/dz2. Show that they are both zero at point Z (where z = −R/2). This shows that the magnetic field varies very little at the point Z. http://i40.tinypic.com/k4b5ag.jpg that link should have the picture. 2. Relevant equations I think the equation for a Helmholtz coil is (4/5)3/2 (uNI/R) 3. The attempt at a solution For part a, I think it's to the left. I could really use some direction for parts B and C. Thanks!