Fun with magnets and permeability.

[CasualKilla]

I think most people (including myself) have a very poor understanding of magnetism. We mostly understand that opposite poles attract and like poles repel, but that is where the intuition ends.

 

I have proposed an experiment to deepen out understanding of magnetism. The experiment holds two magnets N-S at a fixed distance L apart in lets say air. We then measure the force of attraction.

 

The magnets are then lowered into a medium with a higher permeability than the first, such as molten iron (joke but cant think of anything else) and measures the force of attraction.

 

 

Lord wikipedia tells us that this will indeed increase the force:

 

 

But the phenomenon is still strange, the flux will increase in the medium with higher permeability as shown below:

 

 

 

But why does the increased flux or density of flux lines cause the magnets to attracted each other more strongly?

 

Looking at some equations, we will see that the only thing remaining constant between these two states is the MMF and therefore the H-field. But what is determining this fields strength?

 

 

I don't think i really have a question, I am just interested in what is going on and would like to talk about it.

Edited March 17, 2015 by CasualKilla

[swansont]

The bottom image in the link is the magnetic field map of a set of nested high-permeability shells in the earth's field (modeled as vertical and a value of 0.5 gauss) There's an added 1 milligauss field on the interior (owing to how atomic clocks function). I don't recall which shade of orange is 1 gauss, but I'm pretty sure the red is stronger; you concentrate the flux lines as they enter the material.

 

http://tycho.usno.navy.mil/clockdev/Rbdesign.html

[studiot]

Again I am currently short of time but you are missing part of the equation

 

[math]{\bf{B}} = {\mu _0}{\bf{H}} + {\mu _0}{\bf{M}} = {\mu _0}\left( {1 + \frac{M}{H}} \right){\bf{H}} = {\mu _0}\left( {1 + {\chi _m}} \right){\bf{H}}[/math]

Look up susceptibility.

[Sensei]

Just a side note.
Somebody who wants to play with magnetisms should get compass array device (or even couple - you could make experiments with wires, passing current through them, working motors, and other electrical devices).
It costs $28.5. Highly recommend it.

 

 

It's from this shop

http://www.eduvis.pl/oferta/fizyka-pomoce-dydaktyczne/elektrycznosc-i-magnetyzm/zestaw-nr-84-przyrzad-do-demonstracji-linii-pola-magnetycznego-detail

 

[studiot]

 

Sensei

Somebody who wants to play with magnetisms should get compass array device

+1

Never seen one of these, thanks.

[Sensei]

+1

Never seen one of these, thanks.

 

Wow.

It's essential.

There are also 3D versions of it, where magnets are not on needle and rotating in 2D, but "flying in air" connected to grid by elastic material.

 

Brute force method of making compass array device is buying/making hundred compasses like here:

Example 3D versions (68 usd)

(not the best one because needles are still rotating in 2D plane)

It's quite big - needles have 1.5 cm length.

It has 200 and 400 needles-compasses (according to website description).

[CasualKilla]

WOW, some really sick devices guys, I especially like the 3D one. Anybody got ideas of some kind of cheap fluid that has at least twice the permeability of air?

[Sensei]

Now imagine experiment with permeability:

place compass arrays around magnet or electromagnet (with adjusted strength), take photo using digital camera on stand (so it'll be static location). It'll be reference photo (lack of material = just air).

Then place different materials between compass array and source of magnetic field.

And take photos for each material.

Compare results in image editing software.

 

Below them put ruler for easier measurement of distance.

Edited March 19, 2015 by Sensei