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induction magnet / fluorescent bulb

can a long bulb serve the role of the aluminum pipe?
  [vote for,

I am thinking about induction. I understand it just barely, which makes it fascinating. I am thinking of the experiment where a magnet falls slowly down the center of a conductive pipe, slowed by the induced current and cosequent opposing magnetism.

Everyone knows metals conduct electricity. But what about plasma? I think they conduct electricity too. The handiest plasma is that inside a long fluorescent bulb.

I propose that a plugged in fluorescent bulb could serve as the pipe. On placing a ring magnet circumferentially around one end of a vertical tube bulb and letting it fall, I predict that the magnet will fall slower than would be the case if the bulb were unplugged.

Maybe the phosphors in the bulb will glow extra as the magnet passes by?

bungston, May 02 2015

Related: lamp that works this way https://en.wikipedi.../Electrodeless_lamp
[notexactly, May 29 2015]

B-H curve http://www.electron...tic-hysteresis.html
[Ling, Jun 01 2015]


       Or a glass pipe with hollow walls that the plasma can propagate excitedly and the magnets can drop though the centre of the pipe. I would definitely want to see the visual effect of this.
wjt, May 03 2015

       This is a brilliant idea! [+]
MaxwellBuchanan, May 03 2015

       I suspect that there will be an effect, but the gas can move with the magnet whereas usually the aluminium is fixed.
Ling, May 03 2015

       Would make for more interesting streetlights, and very pictureskew scene with lots of council workers singing shanties at the capstan, while hauling the magnets back up to the top of the 200 ft tube.
not_morrison_rm, May 03 2015

       There's a huge and very important difference between an ionized gas (as found in gas-discharge tubes) and a true plasma ...
8th of 7, May 03 2015

       /gas can move/ So induced eddy currents pull themselves apart?
bungston, May 03 2015

       Not sure...I guess the force on the magnet is balanced by the force on the conductor (gas).
Ling, May 03 2015

.I I.
.I I.

       I predict that there will be interesting effects on the tube, much as [bugston] suggests, but the magnet will drop like a rock. Might be best to try with a dc HV supply instead of the standard ac mains.
csea, May 03 2015

       A multi-megohm hv resistor could limit the current. Or Use the HB's favourite hv generator, a van de Graaff.
csea, May 04 2015

       I found a video where a man turns a lit fluorescent bulb on and off by bringing a magnet close to it. I suspect, though, that the magnet is interfering with the action of the magnetic ballast.
bungston, May 04 2015

       If the plasma can slow the magnet, then perhaps you've come up with a method of increasing drag when entering an atmosphere. Generate a strong, static magnetic field along the axis of a spacecraft and pull a bunch of plasma along for extra drag.
TIB, May 30 2015

       Usually when entering an atmosphere you want to get rid of the plasma as quickly as possible, so its heat can't get through the shockwave to your vehicle's surface. But if you drag on it as it flows beside the vehicle, it might be okay.
notexactly, May 31 2015

       Thinking about drag - that is already how a vehicle slows on re-entry: conversion of kinetic energy to heat via friction. If one used magnets to increase the effective profile of the ship by recruiting plasma, would that decrease heating of the hull?
bungston, May 31 2015

       Here is a very easy physics question. A magnet swings past an iron sheet and slows as it passes. Does the kinetic energy lost by the magnet turn into heat of the magnet / iron sheet?
bungston, May 31 2015

       [bungston] I saw this really neat braking system on a salt-flats racer that used what you're describing in your question.   

       A set of, I think it was, 4 magnets were attached to a rotor, that was attached to a wheel. If this was a motor it would be considered an axial-flux arrangement.   

       An aluminum plate was brought either in towards the spinning rotor, or away. As the driver brought the plate closer, the magnets would induce current in the plate, creating a large drag on the rotor and heating the plate. This was the racer could brake without any surfaces touching, with a simple and reliable system.   

       I've considered building a mini version of this to prevent kid#1 from riding his trike faster than about 10km/h, but below that speed not feeling much drag.   

       With regards to your question: A magnet passing over a flat plate conductor will induce current and cause heating (I^2R losses). I'm not sure if the permanent magnet will heat as a result of interactions with the eddy currents. From what I've seen, not substantially. An iron conductor will probably behave differently to something non-ferrous.
TIB, May 31 2015

       I have heard of induction brakes, I think. I very much like the lack of friction: nothing to wear out.
bungston, May 31 2015

       But the magnet! I know current causes heat which subs in for friction in the service of entropy. But what about a plate which is magnetic but nonconductive? No eddy currents. Does plate or magnet heat up thru magnetic attraction alone?
bungston, May 31 2015

       I think that the heating is caused by induced electrical currents in the plate, because the parts of the plate experience a change in magnetic field as they pass by the magnet. The magnet, however, sees the same magnetic field all the time.   

       If the plate is made to be magnetic, but not conductive, then its parts will also experience a change in magnetic field as they pass the fixed magnet. The point to consider here is: does the magnetisation and demagnetisation generate heating effects in the plate? The area in the B-H curve is a possible measure of the energy involved.
Ling, Jun 01 2015

       // But what about a plate which is magnetic but nonconductive? No eddy currents. Does plate or magnet heat up thru magnetic attraction alone? //   

       Like ferrite? Hmm, as [Ling] said, I think. If permanent magnets: it would certainly cog quite badly.
notexactly, Jun 01 2015

       /does the magnetisation and demagnetisation generate heating effects/   

       I cannot recall having read about magnets heating up for any reason other than induction. But if a swinging magnet or anything else can slow purely because of magnetic effects I cannot imagine where else that energy would go.   

       Whenever I start thinking about magnets and their spooky ways I worry I am on the slippery slope to a perpetual motion machine.   

       Ling it usually takes me a few posts to catch up with you. Magnetic hysteresis is the effect whereby change in magnetic field is turned into heat. I wonder if hysteresis could be used to heat a plate, for example to make tea.
bungston, Jun 01 2015


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