Science Buddies: "Ask an Expert"

I tried the "Shake-a-Gen" project in
https://www.sciencebuddies.org/science- ... ?from=Home
But it didn't work. I made about 3000 turns on the can but the thing is that I didn't use the neodymium magnet, I used another strong magnet, stronger than a refrigerator magnet but not as strong as a neodymium one. When I shook it, the voltmeter doesn't read anything, The voltmeter doesn't even move. I also tried it with a LED but still it didn't work The coil around the 35mm film canister is about 1cm thick.
What could be the proble?
-the magnet (not neodymium)
-the coil (ifever it wasn't winded up well in the start)
-any other factors?
Please Help, Thank You

Hi hypark,

The experiment seems to finicky with respect to the number of turns and type of magnet.

Off the top of my head, it would seem that you need a neodymium magnet. Did you try working through the equations with the magnet you have?

I'm impressed 3000 turns! Did you use the bobbin holder (http://www.creative-science.org.uk/wire.html)? If you did manage 3000 turns without any kinks that should work better than 1000 turns. Were there any kinks? That would be a second source of source of something that would need fixing.

does that mean that even one or two kinks could affect the flow of the electricity?

Another thing is,if the coils were winded up perfectly, would it still work even if a common refrigarator magnet is used? or any other magnet instead of the neodymium one?
-could it produce at lease one volt?
(I can't find any neodymium magnets because I'm in the Philippines now and I can't find it anywhere.)

Hi hypark,

I have no direct experience with these types of devices, so I would suggest a careful reading of the experiment details in The Creative Science Centre (http://www.creative-science.org.uk/gensimple1.html).

does that mean that even one or two kinks could affect the flow of the electricity?

The Science Centre wrote: Winding 1000 turns of wire on a former is not easy. The worst thing is when you are 800 turns in and the wire from the reel starts to get all tangled and forms a birds nest ! Click below for details of how to make a bobin holder for the wire reel to stop this happening: http://www.creative-science.org.uk/wire.html

Apparently kinks in the wire are a problem. How much a problem, I don't know. This is why the bobbin holder is suggested.

The peak voltage generated by this little device is given by:

The Science Centre wrote: V = A x M x N

Where A is the cross sectional area of the can (0.0008 m²), M is the rate of change of magnetic field (ca. we need to use very strong magnets having a surface field of say 1 Tesla (see magnet info. below), so shaking it say 5 times a sec we get M = 5 Tesla / sec) and N the number of turns.
If we want an LED to light brightly we need to generate peak voltages of about 4V;

rearanging the formula allows us to estimate the number of turns:

N = V / (A x M) = 4 / (0.0008 x 5) = about 1000 turns - happy winding !

I assume you're trying to use 3,000 windings to use a magnet that is possibly 1/3 the power. Based on the "happy winding" comment above, 3,000 kink-free winding would appear to be difficult.

hypark wrote:Another thing is,if the coils were winded up perfectly, would it still work even if a common refrigarator magnet is used? or any other magnet instead of the neodymium one?
-could it produce at lease one volt?

(I can't find any neodymium magnets because I'm in the Philippines now and I can't find it anywhere.)

with V = N x A x M, it would depend on the strength of the magnet you have. With A = 0.0008 and N =1,000 (which is the number that The Science Centre seems to be recommending as the maximum with very careful winding) to get V = 1, you need M = V / (N x A) or M = 1.25 Tesla/sec.

If you shake 5 times per second, you need M to be (1.25 / 5) Telsa / sec. Or M = 0.25 Telsa / sec. I don't know the strength of refrigerator magnets, but the way that neodymium magnets are described on the Science Centre's pages, it sounds like conventional magnets are not even close in strength to neodymium ones.

One normally would get hard to find items by mail order. Since your project due date is in two days, this method won't work here. I'm at a loss what to suggest, besides modifying your project based on what you've accomplished so far.

May be someone else can help with other suggestions or to correct my math.

There is a magnetic coupling property of magnets and coils that may be involved. The geometry of the magnetic poles (location of north and south poles on the magnet) and the shape and physical size of the magnet affect the shape of the external magnetic field.

If the physical size of the magnet and the distance between its north and south poles is small with respect to the cross sectional area of the coil, the majority of the magnet's magnetic field will not couple strongly to the coil. The formula referenced in previous responses and in the project is for the "coupled magnetic field strength".

To illustrate this magnetic field desnsity property, consider the use of a "keeper" on a horseshoe or U shaped magnet. With the "keeper" in place, the strongest part of the magnetic field is contained inside the magnet and keeper. If you passed this combination by a coil it would not couple well to the coil. If you take the keeper off and pass one leg of through the center of the coil and the other end is outside the coil, you will get very strong magnetic coupling for the few turns that are closest to the gap between the ends and very weak coupling elsewhere.

If your meter is a multi-meter and not just a volt meter and has a DC micro-Amp scale, try using it to measure the current in the coil.

The magnets recommended in this project were not only strong, their geometry was such that the distance of the north and south poles was large with respect to their diameter so they coupled well to a coil with a 35mm film canister core.

Thank you very much.
I think the problem was the magnet. You're right, a neodymium magnet is very different from those ordinary magnets and I think I could solve the problem by buying one of those "shake lights" flashlight so I can use the magnet in the flashlight, (its also a neodymium) since I can't find any magnets here...
So I guess my problem is solved.

hypark wrote:Thank you very much.
I think the problem was the magnet. You're right, a neodymium magnet is very different from those ordinary magnets and I think I could solve the problem by buying one of those "shake lights" flashlight so I can use the magnet in the flashlight, (its also a neodymium) since I can't find any magnets here...
So I guess my problem is solved.

Congratulations, very creative! Please let us know if you have any additional questions.