Viewing magnetic effects on water

After viewing a short youtube video regarding diamagnetism I decided to repeat the experiment using my newly acquired green lab laser. The plan was very simple: slightly elevated flat surface, movable magnet, a few drops of distilled water and a carefully aimed laser beam. Un-fortunately the only flat surface I had on hand was a mirror which I instinctively turned up-side-up, thinking that is the correct way to go at it. Which is of course wrong as I found out later. The laser beam is supposed to bounce of the water surface for that experiment, not the mirror, and the effects on the water surface can be viewed when moving the magnet beneath that area.
(Video can be seen here: http://www.youtube.com/watch?v=2FvWtEdY4sE)

Frustrated by my obvious failure to reproduce a very very simple experiment I kept fiddling with the position of the magnet and the angle of the laser until I managed to get the laser to bounce off the mirror almost exactly at the center point of where the magnetic effect on the water was. Here is the result. Actually, there were two results. Not to far away ( the images were projected on my garage ceiling ) there was a different pattern. Image #2 below.

I can't say that I know what these images represent, but I imagine them being 2D representations of the underlying magnets effects on water. I'd be grateful if anyone could provide a more scientific explanation.

Anyways, here's what I used and how to reproduce the effects.

( Apologies for the blurry images, I couldn't with the tripod... again. )

Step 1 Equipment and materials

Here is what you will need:

1 laser
Any old laser will do red, green, blue, anything within your visual spectrum is just great. The only thing I'd suggest you avoid is using a strong laser. If you're into laser you'll know the ones I mean: the dvd burner, blue-ray, I can cut through duct tape ones. Since you'll be bouncing laser beams off all over the place, I'd urge you to not exceed 50mW and at the very least use some sunglasses for basic protection.

Here's the one I'm currently using: http://www.dealextreme.com/details.dx/sku.10096

1 mirror
Size doesn't matter, it's how you use it. :) No wait! Erase that! Get something small enough to handle with ease.

1 small puck-shaped neodymium magnet
The one I used came with the Arduino sensor pack 900.

1 small metallic strip
or anything that you can use to move the magnet without moving the mirror.

some water
Distilled preferred, but not required.

something to elevate the mirror only slightly above the height of the magnet

[optional] a squid type third hand
It's a priceless tool and if you hadn't built one for your workshop I encourage you try. The most excellent instructable on how to do this is here: http://www.instructables.com/id/Third-Hand-A-multi-use-helping-hand-for-electro/

Comments

[kelseymh]

Is there any chance that you have a drawing program you could use to make a diagram of your setup? In particular, the thickness of the water film and positioning of the laser. I guess that it's that central bit of four-fold symmetry which is showing the diamagnetism (the varying thickness of the water film)? Otherwise, the concentric circles are just the interference between the laser reflection of the top surface of the water, with that off the mirror plane below. From the fringe spacing and laser wavelength (532 nm, most likely), you should be able to compute the thickness of the water plus glass. This is a nice concept, and some good non-obvious science, too. The I'ble could benefit from a bit of theory background, if you're willing to do the research (Wikipedia should be enough).

[vincenc]

Why thank you for you kind reply kelseymh. These images are from a few months ago and I've since had to leave my garage in favor of the builders that are working on the house. They will be done in a few days and I'll then be able to redo the whole thing hopefully being a bit more detailed in documenting everything. Interesting idea about computing the thickness, I've done similar calculations before with the single slit experiment. I'll give that a go too. Kind regards, Vince

[gitm]

If you're familiar with calculating the interference patterns from slits you should also be familiar with the principles of electromagnetism. Particularly that magnetic fields are the result of moving electric fields (and hence the moving electric charges). However, I think the image is the result of waves propagating through the water, thereby changing the orientation of the surface at different locations along the surface. This changing orientation leading to different angles of incidence and therefore bending the light leaving the water by different amounts. I think this would be a good demonstration for second year physics class dealing with optics.

[kelseymh]

Ah, remodeling! Good luck; I hope that things have stayed (even roughly) on schedule for you. It really is a very nice project. If you do get a chance to expand this, a link to some of the literature on using laser interferometry for surface height analysis (e.g., how satellites monitor El Niño), might be a way to jump start the scientifically curious. As an incentive, with a bit of that background stuff, I would be up for Featuring this in a heartbeat. I've already given it a "Good" rating; I can/will bump that up, of course.

[vincenc]

No, ofcorse they haven't stayed on schedule. :) At the time of writing this they are already two weeks behind. My guess is 3 more days till completion.

[joejoerowley]

Great Work Sir! I'm loving the experiment. Is this diamagnetism the same principle behind why MRI works, magnetic water molecules? Thanks, Joe

[vincenc]

I've read only a little bit about how MRI works, but from what I understand using water's magnetic properties is the first step of the entire MRI process. www.howstuffworks.com/mri.htm

[joejoerowley]

 Okay, gotcha. Very Cool. Great Project!

[merlinjim]

Dude, this is awesome!

And I know why ;)  Here comes your scientific explanation:

The pattern you see is a result of interference - basically, even though light is made of particles, it can act like a wave... and just like ocean waves, when they overlap, the crests and troughs add together.

In this case, the initial laser light is "coherent" - meaning all the photons are moving in a wave motion in lockstep throughout the beam.  When the light breaks the surface of the water, a portion of the beam is reflected up and a portion refracted down - based on the angle between the laser and the water.  The more perpendicular the laser beam is to the water, the more of it penetrates down.  This also happens to affect the refraction angle.

The magnet produces a slight dimple in the surface of the water through diamagnetism, it acts like a very slight lens.  The reflected waves are bent by this dimple in one direction (similar to a hyperbolic mirror) and the refracted waves in the opposite direction (hyperbolic lens)

The beam in the water then reflects off the mirror, passes through the air-water interface again (where, once again, it may be subject to both reflection and refraction), then finally bouncing up somewhere to meet the first beam.

The phase of the light at each point throughout the spot determines whether you see a light or dark patch there.  Each area passes through slightly different paths in both the first beam and the second beam - if the first arrives as a crest and the second as a crest, you get a bright area.  If one is a crest and the other a trough, you get a dark spot as the energies cancle out.  If both are troughs, you get a bright spot.  This is because light energy doesn't have a charge - there's no concept in the natural world of a negative amount of light.