# Calculation of Magnetic Field Lines

I am doing some research on how to calculate magnetic field lines for a bar magnet.

So far I have found the following equations: \begin{align} \frac{B_r}{B_\theta} &= \frac{d_r}{rd_\theta}\\ B_r& = \frac{-2M\sin\theta}{r^3}\\ B_\theta &= \frac{M\cos\theta}{r^3} \end{align}

But I cannot find any supporting literature. I was hoping somebody here could direct me in the correct direction.

• Can you please explain the symbols? Not everyone knows. Plus, whatever $d_{\theta}$ is, the first equation looks dimensionally inconsistent. – 299792458 Oct 10 '14 at 20:01
• @New_new_newbie I accidently wrote $d_\theta$ twice, I've corrected it. – Lerp Oct 10 '14 at 20:14
• physicsinsights.org/dipole_field_1.html – Rob Jeffries Oct 11 '14 at 13:14