how many coil turns...help

[oneinaamillion]

I'm helping my son with his Science Fair project and we're having a problem getting any results from his experiment.

We have followed the instructions for the "coil turn" experiment by wrapping the empty toilet tissue tubes with 26 gauge enameled magnetic wire and securing it with masking tape. We have stripped the ends of the wire and applied them to the ammeter. While one holds the wires in place on the ammeter with their fingers the other moves the 1/2 inch steel rod (parallel to the table) within the center of the tube. But with no results (milliamps) registered on the ammeter. Our working surface is a wooden (dining room) table. We have also tried wrapping the toilet paper rolls with other gauges of wire (22, 30) with no results.

Please give suggestions on what we need to do differently to get results.

Thanks

[Louise]

I'm helping my son with his Science Fair project and we're having a problem getting any results from his experiment.

We have followed the instructions for the "coil turn" experiment by wrapping the empty toilet tissue tubes with 26 gauge enameled magnetic wire and securing it with masking tape. We have stripped the ends of the wire and applied them to the ammeter. While one holds the wires in place on the ammeter with their fingers the other moves the 1/2 inch steel rod (parallel to the table) within the center of the tube. But with no results (milliamps) registered on the ammeter. Our working surface is a wooden (dining room) table. We have also tried wrapping the toilet paper rolls with other gauges of wire (22, 30) with no results.

Please give suggestions on what we need to do differently to get results.

Thanks

I think you are talking about this experiment:
https://www.sciencebuddies.org/mentorin ... ?from=Home


First, don't use your fingers to make the connection to the ammeter- if you are touching the bare wire, you could be shorting out the system. [I'm not sure if you are doing this or not from your description] Secondly, make sure that the stripped wire is not touching anything other than the ammeter- don't let the bare wires touch each other.

Double check that you followed all the instructions properly The instructions suggest starting the measurements with the 500 coil set up...

You are sure that your rod is steel or iron? You need a magnetic metal for the current to flow...

Lastly, are you sure you have the ammeter hooked up properly?

The gauge of the wire shouldn't matter- this should produce current for any of them.

Let us know how this goes.

Louise

[ghariman]

Hi there,

I went and looked at the project description that the previous Expert posted:
https://www.sciencebuddies.org/mentorin ... ?from=Home

I think (and please any experts correct me on this) that IF the experiment is to study electric induction due to a magnet THEN instead of using a steel rod you need to insert a MAGNET (and also move it in and out to create the changing magnetic field).

I also went to the Bibliography section on the first link:
http://www.faqs.org/docs/electric/Exper/EXP_4.html (a couple of paragraphs down which has the same picture as in the project description link above).
In specific: http://www.faqs.org/docs/electric/Exper ... 20inductor

After reading that Bibliography link I realized that the experiment with the STEEL ROD is NOT about electric induction caused by a change in magnetic field (and that is the reason why steel rod is being used as opposed to a magnet). Instead this project is to study the effects of inductors. So in order to do this experiment you would need a low voltage AC supply and a lamp. Then when you insert the STEEL ROD it will make the wire-wrap more inductive and thus reduce the average current (and make the lamp dimmer).

Therefore I think that the project description should have the STEEL ROD changed to a MAGNET and that the MAGNET should be moved in and out of the coil of wire-wrap. Then you would see the current changing in your ampmeter.

Any Experts agree/disagree with this ?

I hope this helps and doesn't confuse you further.

[Louise]

Hi there,

I went and looked at the project description that the previous Expert posted:
https://www.sciencebuddies.org/mentorin ... ?from=Home

I think (and please any experts correct me on this) that IF the experiment is to study electric induction due to a magnet THEN instead of using a steel rod you need to insert a MAGNET (and also move it in and out to create the changing magnetic field).

I also went to the Bibliography section on the first link:
http://www.faqs.org/docs/electric/Exper/EXP_4.html (a couple of paragraphs down which has the same picture as in the project description link above).
In specific: http://www.faqs.org/docs/electric/Exper ... 20inductor

After reading that Bibliography link I realized that the experiment with the STEEL ROD is NOT about electric induction caused by a change in magnetic field (and that is the reason why steel rod is being used as opposed to a magnet). Instead this project is to study the effects of inductors. So in order to do this experiment you would need a low voltage AC supply and a lamp. Then when you insert the STEEL ROD it will make the wire-wrap more inductive and thus reduce the average current (and make the lamp dimmer).

Therefore I think that the project description should have the STEEL ROD changed to a MAGNET and that the MAGNET should be moved in and out of the coil of wire-wrap. Then you would see the current changing in your ampmeter.

Any Experts agree/disagree with this ?

I hope this helps and doesn't confuse you further.

My research found the same thing- this exact experiment done with a magnet. That is why I recommended using the exact metals recommended- when I google, I found that steel can be somewhat magnetic.

Then again, the copper wire was specified as being enamelled magnetic (which I hadn't heard of before) , so I thought maybe the two components were flipped.

I may just buy this wire and try this experiment this weekend.
Louise

Louise

[deleted-71588]

If you are trying to measure current flowing through a coil with an amp meter induced by a non-magnetized steel rod, your results match what I would expect.

Even if you change the experiment and use a magnet, you aren't likely to measure the induced current with an amp meter. Most amp meters are made with a shunt resistor and a micro-amp meter such that only 1 part in a million of the current flows through the meter with most of it flowing thorugh the shunt.

What you need is a micro-amp meter.

Increasing the number of turns will increase the effect only if all of the turns are in the changing magnetic field. With a long coil, very few of the turns will be in rapidly changing portion of the magnetic field at any given instance. Wrapping a short multi-layer coil is one way to increase the effect, but I would start with a stronger magnet and a more sensitive meter.

As others have indicated, you need to find a better way to attach the coil to the meter. Having your body in parallel to the meter will introduce a shunt resistance and capacitance and will affect a circuit operating at these small current levels.

[Louise]

Looking at these instructions again, I see it calls for "magnet" wire, not "magnetic" wire, which apparently is just copper wire with insulation that will stand up to lots of coiling (for experiments such as this).

It seems that the instructions for this project need revision.


Louise

[deleted-71588]

After printing out and reviewing the project, I went out a bought a "U" magnet from a hobby store and a three pack of Enamel-Coated Magnet Wire from Radio Shack and did some experimenting with these and a Sperry Digisnap DSA-400 digital multi-meter.

I modified the plastic spool containing the 75 foot 26 AWG (green enamel) by cutting down one flange of the spool so that the U magnet would fit down the center and over the cut down flange. Assuming a 3 inch average diameter and a 1.25 inch long spool, this works out to about 300 turns and about 60 turns per 1/4 inch. Based on the approximate 1/8 inch thick magnet, I estimate the strongest magnetic field to be in about 1/4 inch worth of turns at any given instance.

I used the 2V scale which has an input impedance of 10 Millon Ohms and saw a .017 volt peak with a fast traverse of the magnet. Ohms law V = I * R implies a short term average of .0017 micro-Amps was flowing long enough to be digitized.

I then intentionally broke the U magnet to make a bar magnet and measured a .009 volt peak with about the same traversal speed.

This confirms my suspicions that the project as described will NOT work and I suspect but haven't fully proven:
1) digital meters are a poor choice for this project
2) Analog DC milli-amp meters probably aren't sensitive enough
3) A zero center micro-amp meter is probably the best choice
4) A very strong bar magnet would be needed
5) A U magnet is able to concentrate twice the amount of magnetic flux through a portion of a coil than a bar or rod magnet with the same strength.

I suspect that a higher peak current is flowing for a shorter period than what the sampling rate of the meter I am using can measure.

[Louise]

Glad you tried this out... Radio Shack was closed when I got there last night, so I couldn't get any wire.

Science in action! Always exciting!

Louise

[deleted-71588]

I took a trip to a local salvage store and got lucky. I picked up a old analog Simpson model 127T 0-25 microAmp DC meter (1960 ohms).

Using the Green spool coil setup in my previous post, I'm seeing a peak of 2.5 microAmps.

I modified the Red spool (200 ft of 30 AWG) in a similar manner to the Green spool. Based on the average diameter, I'm estimating this as approximately 800 turns and 160 turns per 1/4 inch. I'm seeing a 5.0 microAmp peak using the U magnet and 2.5 microAmp with the broken off bar piece.

I'm using a pair of mini-clip test jumpers to attach the coil to the meter.

CAUTION: You need to install a shorting device (like a paper clip) on the terminals of sensitive microAmp meters when you transport them.

CAUTION: Unless you can find a zero center microAmp meter, you need to slowly insert the magnet to see which direction the meter moves. If it moves in the wrong direction, continue to insert it slowly and let it bottom out and let the meter settle back into the zero position, then pull it out to take your reading.

Given this additional experimentation on my part, all of my previous suspicions about this project and equipment have been confirmed.

The biggest challenge to someone wishing to do this kind of project will be coming up with an appropriate DC microAmp meter.

Hope this helps.