(Based on Problem 6.4 of Griffiths.) In a magnetic field B, a pure magnetic dipole m experiences a force F = ▼ (m· B). We will now derive this equation. Assume that the dipole is an infinitesimal square with side of size €. Choose axes as shown in the figure below, and calculate ♬ = I √ (ďɩ × B) along each of the four sides. Expand Ễ in a Taylor series on the right side, for instance, х Z ав B = B(0, €, z) ≈ B(0, 0, z) + e მყ (0,0,2) ய Є I € I ►Y