Need help with the magnetic field generated by this current distribution

[Magnetosphere]

Paper on top of disk with fine iron powder.

 

[Magnetosphere]

After I ran the the current through the disk I saw no visible magnetic lines.

 

[Magnetosphere]

With a closer look it appears that the iron powder has grouped somewhat and is raised.

 

[Magnetosphere]

The compass points to south where the current entered the disk.

 

[Magnetosphere]

If I flip the disk the compass points to north

The compass needle also seems to want to follow the outer periphery of the disk, I noticed this with the other side of the disk, south wanted to follow the periphery of the disk.

 

[Magnetosphere]

Conclusion: I could not see any pattern with the iron powder, my observation method may be too crude. The compass did however give definite readings. It would be interesting to see the magnetic field in 3D. I suspect the magnetic field is swirling and that there are definite poles.

 

[Charles Link]

@Magnetosphere Very interesting, but somewhat difficult to reach any definite conclusions. If you want to see the iron powder really respond, make an electromagnet, and you won't need more than about 100 mA of current through the windings of the solenoid (response is about 1000x more with an iron core) to get a huge response. Your results show that you have some kind of residual magnetization after the current source has been removed.

 

[Magnetosphere]

@Magnetosphere Very interesting, but somewhat difficult to reach any definite conclusions. If you want to see the iron powder really respond, make an electromagnet, and you won't need more than about 100 mA of current through the windings of the solenoid (response is about 1000x more with an iron core) to get a huge response. Your results show that you have some kind of residual magnetization after the current source has been removed.

Hi, thanks for the input. Yes, the conclusion is not definite. If I make an electromagnet it will be a completely different experiment. The point here is to see what the magnetic field will look like/behave if I pass a current through the disk radially from the axis outwards.

 

[Charles Link]

Just a word of caution when applying currents to the device that you have: It is very low resistance=without any additional resistors in the circuit, you are essentially short-circuiting your power source, which I'm guessing might be an automobile battery. This really is not its intended use=be careful your power source doesn't overheat and explode, etc...

 

[Magnetosphere]

Just a word of caution when applying currents to the device that you have: It is very low resistance=without any additional resistors in the circuit, you are essentially short-circuiting your power source, which I'm guessing might be an automobile battery. This really is not its intended use=be careful your power source doesn't overheat and explode, etc...

Thanks, great advice! I only gave short bursts of current. I kept an eye on the temperature of the wires as well.

 

[berkeman]

Please stop shorting out that car battery. Even for short periods, it is dangerous to do that.

 

[kuruman]

A few more observations to add to the cautionary posts #99 & #101.
Don't expect to get meaningful information from the compass you are using. It's about the same size as he disk and it cannot detect anything but an average torque arising from the filed you are generating. Also, make sure that you are not looking at the Earth's magnetic field.
It looks like you have too many iron filings. Sprinkle just a enough to form a single layer with gaps in between particles and tap the paper when the current is on safely to make it easier for them to move if they have to. Needle shaped filings work much much better than spherical filings for visualizing magnetic fields.

 

[Magnetosphere]

Please stop shorting out that car battery. Even for short periods, it is dangerous to do that.

Thanks, it was.

A few more observations to add to the cautionary posts #99 & #101.
Don't expect to get meaningful information from the compass you are using. It's about the same size as he disk and it cannot detect anything but an average torque arising from the filed you are generating. Also, make sure that you are not looking at the Earth's magnetic field.
It looks like you have too many iron filings. Sprinkle just a enough to form a single layer with gaps in between particles and tap the paper when the current is on safely to make it easier for them to move if they have to. Needle shaped filings work much much better than spherical filings for visualizing magnetic fields.

Thanks, I only had fine iron powder for this test. The compass reacted to the disk quiet strongly, I am sure this was not the Earth's magnetic field. There was also a clear difference to how the compass reacted to the top of the disk versus the bottom..

 

[Magnetosphere]

Perhaps this image is true after all. Considering how the compass reacted to the outer periphery of the disk, as if the magnetic force was concentrated on the edge and following the edge around the disk, also keeping in mind that the compass showed different poles.

 

[Tom.G]

The images from posts 92 & 93 (repeated here) suggest the magnetic field is perpendicular to the surface. That is also compatible with the magnetic compass pointing differently on the two surfaces of the disk.

You might get some magnetic field imaging film. It is even available on Amazon:
https://www.amazon.com/s/?ie=UTF8&keywords=magnetic+film+viewer&tag=pfamazon01-20

Cheers,
Tom

 

[Magnetosphere]

The images from posts 92 & 93 (repeated here) suggest the magnetic field is perpendicular to the surface. That is also compatible with the magnetic compass pointing differently on the two surfaces of the disk.

You might get some magnetic field imaging film...

Good observation, it also looks (if you look at the out of focus part at bottom) like the powder is "turning" to the right, it is far from conclusive though. I will get the magnetic film and do the experiment again.
It seems that the strongest magnetic force is at the edge, when I moved the compass closer to the axis it seemed to loose it's "grip", however it does not mean that there is no magnetic field on the inside, it may just mean that the field is weak on the inside of the periphery and strong just at the edge where it completes its loop. One thing that is conclusive is that the compass is showing two poles.

 

[kuruman]

It seems that the strongest magnetic force is at the edge ...

Don't forget that all the current that is fed into the center of the iron disk is drained by the brass ring around the edge. Near the edge, I would expect the compass to respond to the magnetic field generated by the current in the brass ring not to the current in the iron disk. You need to place the compass away from the edge to test the field in the iron. Of course, if the compass is the size of the disk, you cannot do that.

 

[Magnetosphere]

Don't forget that all the current that is fed into the center of the iron disk is drained by the brass ring around the edge. Near the edge, I would expect the compass to respond to the magnetic field generated by the current in the brass ring not to the current in the iron disk. You need to place the compass away from the edge to test the field in the iron. Of course, if the compass is the size of the disk, you cannot do that.

I only gave the disk a few short bursts of current and used the compass after, since brass is not magnetic the magnetism can only come from the iron. I did place the compass closer to the axis (#106... it seemed to loose it's "grip") when I moved it away from the axis it wanted to follow the edge, see #95.

 

[kuruman]

I only gave the disk a few short bursts of current and used the compass after, since brass is not magnetic the magnetism can only come from the iron. I did place the compass closer to the axis (#106... it seemed to loose it's "grip") when I moved it away from the axis it wanted to follow the edge, see #95.

Is the purpose of this exercise to map the magnetic field from the presumably permanently magnetized disk after you have pulsed a (mostly) radial current through it? The original statement of your question

Homework Statement

A DC current is flowing between two electrodes through a iron disk medium. Positive is attached to the copper shaft of the disc and the negative is attached to the outer brass periphery of the disk. The radius of the disk is 2,54mm (1 inch) and the height of the disk is 1cm. How does the magnetic field look/behave when a DC current is applied to the disk?

made me (at least) believe that you wanted to map the magnetic field while the current is running. Which is it, after or while?

 

[Magnetosphere]

Is the purpose of this exercise to map the magnetic field from the presumably permanently magnetized disk after you have pulsed a (mostly) radial current through it? The original statement of your question

made me at least believe that you wanted to map the magnetic field while the current is running. Which is it, after or while?

Hey, yeah, to me it is basically the same thing when it is turned on and turned off, the iron in the steel is magnetized and keeps its magnetic forces aligned for a while after current is off. I need to know the behavior, where is the south pole/north pole mainly. It appears that my drawing could be correct considering how the compass needle behaved. However, everything is still not clear, but it seems that we have at least some credible information.

 

[kuruman]

If it's the same to you, then your answer is after the current is turned off. Currents running in wires generate magnetic fields in the absence of iron. These fields disappear when the current is turned off.

 

[Magnetosphere]

If it's the same to you, then your answer is after the current is turned off. Currents running in wires generate magnetic fields in the absence of iron. These fields disappear when the current is turned off.

Yes the wires produce a magnetic field while the current is there, but the mass of the wires compared to the mass of the disk is minuscule and the produced magnetic field in the wires will not affect the disk nor the compass in any way. This time the readings with the compass were done with the power turned OFF due to the risk while short circuiting the battery. Next time I will do the readings with the power turned ON as I plan to install a resistor and study the magnetic field in 3D. Bellow is a summery of what happened in comparison to my drawing, I am not sure if the arrows in the drawing have the right direction. What is more important is that two poles have been confirmed and apparently a magnetic field that is running around the axis.

 

[kuruman]

Whatever you do, be sure you do it safely and consider he cautionary suggestions posted here. It wouldn't be a bad idea to wear eye protection and have an appropriate fire extinguisher handy.