MAGNETIC FIELDS IN MATTER — Edward Purcell & David Morin
Physics — E&M · dipole-field-lines
Problem
A field line in the dipole field is described in polar coordinates by the very simple equation r=r0sin2θ, in which r0 is the radius at which the field line passes through the equatorial plane of the dipole. Show that this is true by demonstrating that at any point on that curve the tangent has the same direction as the dipole field.