woelen
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Nice demo of induction current
This time I have made a web page about a physical subject, the production of induction current around a closed loop when a changing magnetic field is
going through the closed loop.
http://woelen.homescience.net/science/physics/exps/induction...
I think that this is a very nice experiment, also for teachers, because it requires no special equipment, just some tubes, copper wire, a diode, a LED
and a suitable magnet.
Btw, my children like the crude flashing device I made very much. They keep on shaking it, producing bright flashes of white light 
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chemrox
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Nice work. BTW that looks like a cow magnet.
"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
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hissingnoise
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I don't think you mean a pedigree bull chemrox---but I seem to remember something about cows being made to swallow magnets to attract whatever bits of
iron-or nickel-or even cobalt they'd eaten. . .
Or am I missing the nail completely?
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12AX7
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Indeed, that's what they do. Keeps metal-bits from poking holes in their stomachs. An NdFeB magnet would be a bit strong for that purpose, however.
Woelen: great! Now close the magnetic circuit with iron pole pieces to dramatically boost output, and add more windings* to generate power
continuously during a cycle. Also, for 'duh' factor, put two antiparallel LEDs on there, so you don't waste one of the shakes. 
*Winding = a bundle of copper. Windings are measured in turns, so your single winding has 1450 turns. The simplest transformer has two windings,
etc.
A more powerful demonstration of induction can be seen here:
http://www.youtube.com/watch?v=ro6Dt9g7Ohw
Tim
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woelen
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Tim. thanks for your comments. Tomorrow I will change the webpage and use the correct words for windings and turns.
I also ordered a spool of copper wire, 0.15 mm diameter. This spool has 220 meters of wire, so the number of turns is doubled. I also intend to buy a
better LED (there are 40000 mcd LED's available at 30 mA current and 3.0 forward voltage drop) and with these modifications I think I can make the
device even better. It also is a nice idea to use two LED's, antiparallel. But before I can do so, I need to buy more LED's of the same color and
type.
Btw, with the simple 1N4001 diode I do not spoil the power of one of the shakes, but I spoil half of the power of each shake. During each move of the
magnet (forward and backwards) the LED blinks, but only when the electromotive force is in the right direction. I also could use a 4-diode rectifier
(e.g. using Schottky diodes to keep voltage drop low), but this adds complexity to the system and for demonstration purposes that makes the device
less appealing. Using two LED's antiparallel indeed would be a better option.
[Edited on 22-10-09 by woelen]
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chemoleo
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Very nice, very simple!
Reminds me of asking my physics teacher a long time ago: Where/how is the work put into the system? Where does the energy come from?  (assuming a frictionless system)
Never Stop to Begin, and Never Begin to Stop...
Tolerance is good. But not with the intolerant! (Wilhelm Busch)
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Sedit
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Surely Woelen could explain this much better then myself but the energy is put into the system thru the act of turning the tube over. Right before the
magnet falls its potential energy is at its highest which is converted to kinetic energy as it falls. The coil and magnet convert this kinetic energy
into electrical energy used to light the LED.
Knowledge is useless to useless people...
"I see a lot of patterns in our behavior as a nation that parallel a lot of other historical processes. The fall of Rome, the fall of Germany — the
fall of the ruling country, the people who think they can do whatever they want without anybody else's consent. I've seen this story
before."~Maynard James Keenan
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franklyn
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Cute but it reveals little about the nature of alternating current.
You can relay the magnets motion to another coil with a toy
compass along side as shown below. The needle will alternately
point to one end of the nearby coil or the opposite end exactly
in step with the motion of the magnet through the other coil.
Suspending the magnet from a rubber band and tugging down
and releasing it displays what is termed simple harmonic motion
the basis of the alternating current sine wave form.
Cut the loop of three rubber bands and tie both ends of one
band to one end of the other two to make a long band of
40 or 50 centimeters. Attach one end to the magnet and
the other to a fixed point overhead.
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woelen
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I tried the experiment with the campass, but it does not work. The fields are too fast and too much pulse like. If you are lucky you just see the
needle shake a little. It does work though when a DC power supply is used for powering the coil (a few tens of mA of current already gives a good
readout).
I made a new device, now using a coil with 3000 turns and a full wave rectifier, using Schottky diodes. The result really is impressive. Just moving a
neodymium magnet through the hole by hand already leads to two flashes, quickly after each other. No vigorous shaking needed, no quick withdrawing
needed.
A diagram of the system:
When the capacitor is omitted, then a really impressive behavior is obtained. When a 1 F goldcap is used, then you need to shake for a while in order
to charge the capacitor and if the capacitor is charged well beyond 1.5 volts, then shaking leads to a more or less constant light output and when
shaking stops, the light output slowly decreases and the capacitor remains charged at appr. 1.5 volts. So, you only need to shake for a long time the
first time when a fresh capacitor is used. Goldcaps keep their charge for a very long time
I'll extend my webpage on this subject and add more pictures and videos.
Unfortunately it does not work as well with normal diodes, such as the 1N4001. These normal diodes have forward voltage drops well over 0.7 volts and
when they carry a little more current, then this may be even 0.8 volts. A regular schottky rectifier diode has just 0.3 volts forward voltage drop in
a circuit like this.
There also is another very funny effect. If the circuit with the LED is connected to the coil, or when the coil is simply shorted or a resistor is
placed between the terminals, then you feel that pulling the magnet through the coil takes some effort. If the coil is open circuited, then you don't
feel anything special. This is another beautiful demonstration. You feel that you have to provide power to the system. Mechanical energy is
transformed into electrical energy.
[Edited on 28-10-09 by woelen]
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12AX7
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The extreme example, of course, being a heavy copper pipe. If you want to make a demostration, you could lay out a few of these devices, showing the
behavior of a rather strong magnet around simple devices (conductive metal, windings, etc.).
Tim
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franklyn
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Quote: Originally posted by woelen  |
I tried the experiment with the campass, but it does not work.
The fields are too fast and too much pulse like. If you are lucky
you just see the needle shake a little. |
A variety of things could account for this. A neodymium magnet
will affect a compass needle out to 1/2 meter away , if oriented
in opposition to the coil , it will cancel any motion. The coils should
be set far apart and perpendicular ( magnet coil verticle , compass
coil horizontal and allowed to point North ) The magnet needs to
move at not more than 2 cycles per second ( twice each way )
through the coil , with a long stroke. If the rubber band is too
taught add more sprung weight to provide inertia.. Realize that
the miniscule current to light an LED does not compare. Also ,
I should have mentioned that a ferrous core in the compass coil
will greatly augment the field realized there.
The basic demonstration of Faraday's principles is just this
but using a moving-coil d'Arsonval Galvanometer.
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woelen
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I have perfected the demonstration, using a more sensitive coil (having 3000 turns) and the effect now really is amazing. I soldered all things on a
little PCB in order to make a more permanent demonstration tool. This tool is really fun to have around. My family likes to play with it, just moving
the magnet through the hole, making very bright flashes. The device now also is much less vulnerable.
http://woelen.homescience.net/science/physics/exps/induction...
I think that a device like this also is very useful for raising interest in science and technology in young people.
More experiments with this device can be expected in the near future. I also want to try things with big capacitors (goldcaps) and with
LC-oscillators.
[Edited on 1-11-09 by woelen]
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franklyn
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The classic demonstration
http://web.mit.edu/8.02t/www/802TEAL3D/visualizations/farada...
Quoting myself from above
" The basic demonstration of Faraday's principles is just this
but using a moving-coil d'Arsonval Galvanometer.'
_________________________________________
Nice device this , neat and well done
http://woelen.homescience.net/science/physics/exps/induction...
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smuv
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There is another similar experiment, dropping a magnet down a non-magnetic metal pipe (copper, aluminum). Make sure the pipe isn't grounded. If you
get the conditions right, the magnet falls REALLY slowly down the pipe. It almost seems to float down.
[Edited on 12-29-2010 by smuv]
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IrC
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| Quote: Originally posted by 12AX7 | Indeed, that's what they do. Keeps metal-bits from poking holes in their stomachs. An NdFeB magnet would be a bit strong for that purpose, however.
Also, for 'duh' factor, put two antiparallel LEDs on there, so you don't waste one of the shakes. |
A friend with a farm told me about his neighbor trying that. Magnet was too strong, locked itself in one section of intestine with metal in another,
blocking everything killing the cow. Besides the thin coat is little barrier especially if there is a crack, and the metals inside and/or compounds
formed will likely be a poison. I love Nd burgers in the morning. Not.
Add a capacitor and keep going until you have the forever flashlight I keep for times of no power.
I have also heard stories of children getting blockage and infections in their guts from swallowing two of these magnets. No doubt cows prefer the
taste of those alinco magnets shaped like a shiny suppository. Or do they?
"Science is the belief in the ignorance of the experts" Richard Feynman
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franklyn
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@ woelen
This is the sort of thing you like " Building a magnetic heat engine "
http://scitoys.com/scitoys/scitoys/magnets/magnets.html#curi...
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Morgan
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Close up view of magnetic wheel
http://www.youtube.com/watch?v=bzmHGmAqMJc
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IrC
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http://www.mikeware.demon.co.uk/index.html
Woelen I noticed this link on photography does not work. What is the chance of you doing a section on developing color film?
Also could you add an experiment on the single AA cell HomoPolar Motor? I would like to see a good writeup and description on this one as it still
warps my brain trying to think about it.
http://www.youtube.com/watch?v=DirWnQw5o1w&feature=relat...
[Edited on 10-13-2012 by IrC]
"Science is the belief in the ignorance of the experts" Richard Feynman
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franklyn
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@ IrC
Some Simple Demonstration Experiments Involving Homopolar Motors
http://www.sbfisica.org.br/rbef/pdf/060904.pdf
Faraday Homopolar motor
i = current ( conventional flow , + => ( - )
ω = angular velocity
This video shows (+) polarity down into the magnet ( the reverse of the
drawing above ) so instead it rotates clockwise viewed from above.
http://www.youtube.com/watch?v=EkU_JmtH3PU
* Note : Corkscrewing the wire around the axis as shown in your video
greatly reduces the torque produced since the rotational force is now only
a partial vector of the principle force acting at right angle to the wire's length.
Rolling Homopolar motor
http://www.youtube.com/watch?v=q-mJl8IdmgI
Laplace Rail , is the same thing reacting to fixed rails powered externally.
http://www.youtube.com/watch?v=_-kQans2rww
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IrC
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Corkscrewing the wire : If I had to guess I think the guy did this to keep it stable and as centered as possible for purely mechanical reasons, i.e.,
so it would remain in rotation without flying off the battery. I have build many of these, one using a 3 inch N52 magnet and it really is hard to keep
the wire from flying off.
"Science is the belief in the ignorance of the experts" Richard Feynman
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franklyn
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So much for the magnetic field , now what about the electric field ?
Here is an updated demonstration with origins back to the 18 th century
www.youtube.com/watch?v=UdV_fEbRqss
In case you miss it , turning off the TV starts the movement.
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