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Author Topic: Please Explain  (Read 242 times)

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I thought a topic on some !please explains! would be a good idea.

So if you come across something you find odd,then whack it in this thread,and some other members may be able to explain it to you.

So,here is the first one.
We know when we drop a magnet through a copper tube,or any tube made of conductive material,that the fall of the magnet through the tube is slowed as the tube acts like a shorted turn,and lenz takes over.

Well,that is what i thought until Lasersaber posted this video a week ago.

Why dose the magnet fall through the carbon tube(which is very conductive) at free fall speed ?

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


Brad


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Yes, I agree this is difficult to understand.
Definitely looking forward to a logical explanation on that.

Here is another one I don't understand.

A few months ago I wound a coil using thin vinyl coated Iron garden wire.
My thinking was the magnet would get attracted to the Iron coil and at TDC power the Iron coil to kick away the magnet.
Simple enough but I found there was no Inductance value to the Iron coil even though I had a few hundred turns.
I understand the Iron wire has more resistance then copper wire but it is conductive, so why does it not become Inductive when wound in a coil as copper does?

Is there's something about copper we are not considering or don't understand?
Aluminum has about the same characteristics as copper but a little more resistive.

Here's another idea, what if we fill a thin wall 2mm plastic tube of 100 feet long with Mercury and make a coil with it. Would it create a magnetic field and if so. would it have any advantage over a copper coil?

Cheers
Luc
   

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Why dose the magnet fall through the carbon tube(which is very conductive) at free fall speed ?
Because the Carbon tube's resistivity sucks.
His ohmmeter does not have enough resolution to measure the difference between Carbon and Copper.

Simple enough but I found there was no Inductance value to the Iron coil even though I had a few hundred turns.
How did you determine that?
Did this iron coil have an iron core, too ?
   
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How did you determine that?
Did this iron coil have an iron core, too ?

No Iron core, just an Iron air coil.
First I hooked it up to the PS and it didn't become an electromagnet, so I then hooked it up to my Inductance meter to find it had next to no inductance.
Keep in mind the wire is made in China and probably form the cheapest recycled garbage metals the can make wire out of, so it's far from being pure Iron if that can make that much of a difference?

Regards
Luc
   
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...
Why dose the magnet fall through the carbon tube(which is very conductive) at free fall speed ?
...

Question of resistivity. It's not possible to properly measure the copper tube resistance with the Lasersaber's ohmmeter, it is too low.
   
Copper  1.68 10-8  Ω.m
Iron      9.71 10-8
Carbon  3->60 10-5

Carbon is a thousand times less conductive than copper, no wonder that induced currents are not sufficient to significantly slow down the magnet.





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Question of resistivity. It's not possible to properly measure the copper tube resistance with the Lasersaber's ohmmeter, it is too low.
   
Copper  1.68 10-8  Ω.m
Iron      9.71 10-8
Carbon  3->60 10-5

Carbon is a thousand times less conductive than copper, no wonder that induced currents are not sufficient to significantly slow down the magnet.

Seems odd that we would use such a resistive substane for the brushes in electric motors and generators.


Brad


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Seems odd that we would use such a resistive substane for the brushes in electric motors and generators.


Brad

You can trust the engineers, they have a practical sense. The carbon length is short, the contact resistance is probably lower at the carbon/copper interface than at a copper/copper interface, because carbon wears out on rotating copper contacts by conforming to the shape (which also prevents copper from wearing out).


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Believing something false does not make it true.
Seems odd that we would use such a resistive substane for the brushes in electric motors and generators.


Brad


Hi Brad,

For high current applications I have seen brushes that use a copper carbon compound such as the ones at this link:

http://www.morganelectricalmaterials.com/en-gb/products/carbon-brushes/

I have seen them on large industrial motors and on some high torque starter motors.

Carroll


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Hi Brad,

For high current applications I have seen brushes that use a copper carbon compound such as the ones at this link:

http://www.morganelectricalmaterials.com/en-gb/products/carbon-brushes/

I have seen them on large industrial motors and on some high torque starter motors.

Carroll

Indeed.
I have them in my large DC motors.


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yes a sacrificial matrix where the carbon is a binder too

one thing which jumps out is the conductivity claims for "one layer properly oriented" Graphene ,being 1000 times more conductive than copper .


William Barbat told us this years back

   
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