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peteshimmon
2018-Apr-15, 04:16 PM
This is the second possible experiment that I wonder has been done. It is now about two hundred years since experimenters found moving conductors pass magnets produces an electric current. And so much has been done with this! But then how do transformers work? Nothing moves! It must be that an increasing and decreasing field has inherent movement! So let us get an electromagnet, white formica board, iron filings and something to keep the board agitated and the filings dancing around while the current in the magnet coil underneath the board is varied. The lines should keep reforming as larger or smaller and showing movement. Should be fun and a good science museum exhibit!

grapes
2018-Apr-15, 04:56 PM
You're illustrating that a changing magnetic field causes an electric field, and a current, in the first example?

What are you illustrating with the formica board experiment? Turning the transformer on and off also turns the magnetic field on and off? What movement? Would you move the magnet around?

profloater
2018-Apr-15, 05:34 PM
A transformer without restraint would move and indeed many hum as their iron laminations move. In fact you have to work hard to constrain all the parts for silent running. The magnetic field grows and shrinks so your intuition is correct but we don't normally call it movement of the magnetic field. If you consider a solenoid which is like a transformer, it will attract an iron plate and if alternating current is used, it becomes a buzzer. But there's a lot more fascinating stuff about transformers in all their many manifestations.

profloater
2018-Apr-16, 12:45 PM
an experiment we did at school is probably not allowed now. We had a simple coil of wire suspended in air with its bottom end in a small pool of mercury, ( we had a lot of experiments with mercury back then) when a small current is applied the coil contracts, leaps out of the mercury and then falls back repeating the performance. The fact that I can remember and understood the point being demonstrated vindicates those simple school demos.

peteshimmon
2018-Apr-17, 11:20 AM
Well I do have a nice thick volume on transfomers in my electrotechnical bookshelf. Have to look it up again sometime. Actually I have wondered if there is such a thing as transparent colloid material. A magnet immersed in such stuff should show lines of force in three dimentions. Would make a nice executive desk toy!

profloater
2018-Apr-17, 05:30 PM
There are transparent colloids but not necessarily capable of aligning with lines of force. For example biologically bound iron is often in tap water and begins to break up and oxidise to insoluble iron oxide when exposed to the air. Most household uses of water are too temporary to notice this but chronic drips for example show the characteristic rust stains as the iron oxide finds tiny triggers to build on. in very high voltage trasformers the heat losses are taken into oils. If you see one with a transparent lid the oil makes spectacular fountains when the transformer is working. Maybe what you want is a gel with iron filings. 2D versions are used to read fields and a 3D version would be feasible. Ferrofluids have been mentioned recently in the context of fluid seals.

Geo Kaplan
2018-Apr-17, 06:39 PM
Well I do have a nice thick volume on transfomers in my electrotechnical bookshelf. Have to look it up again sometime. Actually I have wondered if there is such a thing as transparent colloid material. A magnet immersed in such stuff should show lines of force in three dimentions. Would make a nice executive desk toy!

Do a search for "Bitter pattern" or "Bitter technique" (named for magnetics expert Francis Bitter). In its classic incarnation it uses ferrofluids (as has been suggested in this thread already). Wayyy back in my student days, we used the technique to reverse-engineer the data storage formats of magnetic-stripe cards. Amazing what one can learn from such a simple method (e.g, number of tracks, linear bit density, etc.).

profloater
2018-Apr-18, 09:02 AM
or you can learn some Hindi while confirming Faraday.

https://www.youtube.com/watch?v=prGlwmSOdr0