# Calculating current through solenoid?

1. Feb 24, 2015

### scoopaloop

Not for a class or anything, just out of curiosity, how would you calculate the current in a solenoid, not given a magnetic field, but just using a bar magnet? I know it will just be some form of Faraday's law. E=N(dphi/dt). Maybe not. I'm imagining all I'm really missing is how to calculate the magnetic field of the magnet. Thanks.

2. Feb 24, 2015

Take the solenoid and connect a voltmeter or multimeter across it. Move the barmagnet towards the solenoid and there should be a deflection in the voltmeter because $\phi$ changes when you keep moving the barmagnet.
or as you know, the bar magnet is also like a solenoid. The expression for magneticfield for barmagnet along axis is $$B=\frac{\mu_0}{4\pi}\frac{2m}{r^3}$$

3. Feb 24, 2015

### scoopaloop

So, just a little clarification, I did a little research online, is M the magnetic strength of each pole and r, I take it is the distance?

Thanks btw.

4. Feb 24, 2015

M is the magnetic fipole moment. Here, $m=n(2L)I(\pi a^2)$