B Changing magnetic polarity of an electromagnet

[fmorgan2]

I would like to change the polarity of an electromagnet. I have reversed the wires attached to a 9 volt battery that wound about a bar magnet but this did not seem to make the north pole become the south pole.
Thanks for your assistance,
Frank

 

[Gordianus]

Reversing the wires is the right solution. How do you know the poles didn't change?

 

[Charles Link]

From what I have read, it takes a considerably strong applied magnetic field to change the direction of polarity of a permanent magnet. One way to do it with a weaker magnetic field is to heat the magnet above its Curie temperature, and then apply the magnetic field. It comes as no surprise that you could not get the poles to change with even moderately strong electrical currents in the coil of the electromagnet.

 

[Orodruin]

to change the direction of polarity of a permanent magnet.

An electromagnet is not a permanent magnet.

 

[Gordianus]

The OP said electromagnet. The case with a permanent magnet Is different.

 

[Charles Link]

The OP said electromagnet. The case with a permanent magnet Is different.

I think the OP needs to clarify what he is using in the core. If it is a soft iron core, the polarity should simply depend on the direction of current, and he would find it a simple matter to get the polarity to reverse.

 

[DaveE]

Maybe you're seeing residual magnetization of the core? As if the first current pulse magnetized it while it was killing the battery. Then when you reverse the terminals there's no (or not enough) reverse excitation?

Try a new battery or measure the current somehow. You're intuition was correct, I think. Something isn't what you think it is on your lab bench.

 

[Dale]

reversed the wires attached to a 9 volt battery that wound about a bar magnet

It sounds like the OP has an electromagnet wound around a permanent magnet.

 

[Vanadium 50]

It's a pity that the OP hasn't come back to answer these questions - he's been back to PF, just not this thread. So we're guessing.

I for one would like to see a detailed description of the setup. With numbers and everything.

 

[DaveE]

BTW, you'll probably need a real low voltage high current power supply to do anything useful. A 9V battery just can't do much.

 

[Vanadium 50]

That's one reason I asked for numbers.