# What is the average magnetic dipole moment?

1. Sep 19, 2011

Though this might be absurd, I would seriously like to know the average magnetic dipole of a magnet. For example, you might consider a regular magnet in a remote control car's motors, or any other suggestions too. And I have one more doubt- I know that e.m.f=-d(phi)/dt and phi=integral(B.dS). So, could we use e.m.f=-S.(dB/dt)???

Thank you,

2. Sep 19, 2011

Staff Emeritus
How long is a piece of string?

3. Sep 24, 2011

length of a string ??? I don't get you... Could you please explain ????

4. Sep 24, 2011

### BruceW

A magnet generally creates a complicated magnetic field. But usually, we approximate that the magnetic field is a dipole field in the approximation of large distances from the magnet. In other words, this equation won't work close to the magnet, but it is a useful approximation when not close to the magnet:
$$B=\frac{\mu_0}{4 \pi} \frac{m}{r^3} \sqrt{1 + 3 sin^2(\frac{\pi}{2} - \theta)}$$
Where $\theta$ is the angle from the dipole axis. And m is the dipole moment.

So this equation would give you the magnetic moment if you could measure the magnetic field of the magnet.

I'm not sure what you mean by the average magnetic dipole?... Surely it is only one value which depends on the type of magnet.

5. Sep 24, 2011

### Staff: Mentor

He's indirectly telling you (by asking a similar sort of question) that your question is unanswerable without further information.