Electromagnetic Induction with Copper Plate, Magnet, and Liquid Nitrogen

On March 16, 2010, I attended a meeting of Physics Northwest (PNW) where I presented one of the demonstrations I use to illustrate electromagnetic induction & magnetic braking. You take a large slab of high-conductivity, oxygen-free copper (mine is 10 inches in diameter & 1 inch thick) and place a very strong neodymium magnet atop it (my magnet is one from www.wondermagnet.com). As the magnet moves in the vicinity of the copper conductor, there is a changing magnetic flux through the copper which - in accordance with Faraday's Law - will induce eddy currents within the copper disk. These eddy currents then interact with the magnetic field of the magnet, producing - through the right(left)-hand-rule - a force which opposes the original motion of the magnet.

For added physics pizzaz, we added in some liquid nitrogen. The LN2 cools down the copper, reducing its electrical resistance and allowing there to be a much larger induced current in the disk. The increased current then leads to much larger magnetic braking forces. This leads to all manner of really awesome effects, many of which seem almost magical if the observer doesn't understand the underlying physics. Even for someone who *does* understand the physics, it's still pretty awesome. This is one of the best demos I do all year, and my students are always excited to play with the setup!

Physics Northwest (PNW) is a teacher-driven organization in the northern & western suburbs of Chicago which meets regularly for fellowship and sharing of demonstration, lab, and classroom tips & tricks. If you'd like to know more about us, visit our website at http://www.edline.net/pages/Physics_Northwest

For more information on these kinds of neat demonstrations and my thoughts on science & skepticism, check out my personal blog, The Skeptical Teacher: http://skepticalteacher.wordpress.com

Category:

Education

Tags:

• physics
• education
• electricity
• magnetism
• electromagnetism
• magic
• skeptic
• skepticism
• physics northwest

[aomimezura11]

nerds! although, it is pretty cool.

[FoamKittyGamer]

@travers114 Aluminum? Reminds me of the balsamic wood + aluminum foil "ionocraft" in a way. Perhaps the same basis involving static.

[roidroid]

@travers114 that would make a great video

[travers114]

@roidroid What i mean is the window has aluminium borders that run from floor to ceiling, so if I put my magnet near the top of the frame and release it, it will slowly fall towards the ground. It's only 2 inches across and a half inch thick i believe. Cost me $20 bucks, but the shipping was $30.

[roidroid]

@travers114 how big is your magnet, to catch an entire window frame?

[travers114]

@travers114 What am I saying NO2, I mean LN2.

[travers114]

Magnetic eddies are amazing. I've got about the same size neodymium magnet as you, but I am lacking the giant copper disk or NO2, so instead I use my window frames. They are aluminium so I can place it well above my head and watch it slowly fall down to land gently on the floor. One of the coolest magnetic phenomena and it blows people minds when I show it to them.

[ladymcse07]

"Quick, get some ice!" :-)