{"id":2673,"date":"2008-06-05T08:56:51","date_gmt":"2008-06-05T08:56:51","guid":{"rendered":"http:\/\/scienceblogs.com\/principles\/2008\/06\/05\/fun-with-thermal-resistance\/"},"modified":"2008-06-05T08:56:51","modified_gmt":"2008-06-05T08:56:51","slug":"fun-with-thermal-resistance","status":"publish","type":"post","link":"http:\/\/chadorzel.com\/principles\/2008\/06\/05\/fun-with-thermal-resistance\/","title":{"rendered":"Fun With Thermal Resistance"},"content":{"rendered":"

In the last few weeks, I’ve been wrapping up E&M, which has included talking about Faraday’s Law and induced currents. I did the traditional demonstration using a PASCO ring launcher<\/a> to demonstrate Lenz’s Law, showing that the induced current flows in a direction that creates a field opposing the change in magnetic flux. The ring launcher uses an alternating current in a solenoid to shoot a metal ring a meter or so up in the air, which always gets a good reaction.<\/p>\n

The extreme version of the same basic physics is the Meissner Effect<\/a>, in which currents in a piece of superconductor completely cancel any magnetic field attempting to enter the superconductor, allowing you to levitate small magnets, or trains. We have a Meissner Effect demo kit, with a piece of high-T superconductor and a rare-earth magnet, so I brought some liquid nitrogen up from the basement to demonstrate this.<\/p>\n

Of course, having lugged four liters of LN2 upstairs, I needed something more than just a floating magnet to show for it, but I didn’t have anything breakable lying around. I did, however, have the aforementioned ring launcher…<\/p>\n

<\/p>\n

If you cool aluminum to liquid nitrogen temperature, the resistance drops by about a factor of five. That means that the same changing magnetic field induces a current that’s five times larger, and thus a launching force that’s five times bigger.<\/p>\n

At room temperature, the launcher will pop an aluminum ring up into the air to about my head height. After cooling the ring in liquid nitrogen, it hit the ceiling with a satisfying thunk. Watching the students in the front row scramble away from the cold aluminum ring like it was fresh from the forges of Mordor was a hoot, too.<\/p>\n

I doubt they’ll really take away anything useful from the demo itself (we talked about the temperature dependence of resistance a few weeks back, but I didn’t spend much time on it today), but it was a fun way to spend part of the last class of new material…<\/p>\n","protected":false},"excerpt":{"rendered":"

In the last few weeks, I’ve been wrapping up E&M, which has included talking about Faraday’s Law and induced currents. I did the traditional demonstration using a PASCO ring launcher to demonstrate Lenz’s Law, showing that the induced current flows in a direction that creates a field opposing the change in magnetic flux. The ring… Continue reading Fun With Thermal Resistance<\/span><\/a><\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"1","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[8,13,7],"tags":[],"class_list":["post-2673","post","type-post","status-publish","format-standard","hentry","category-academia","category-education","category-physics","entry"],"_links":{"self":[{"href":"http:\/\/chadorzel.com\/principles\/wp-json\/wp\/v2\/posts\/2673","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/chadorzel.com\/principles\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/chadorzel.com\/principles\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/chadorzel.com\/principles\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"http:\/\/chadorzel.com\/principles\/wp-json\/wp\/v2\/comments?post=2673"}],"version-history":[{"count":0,"href":"http:\/\/chadorzel.com\/principles\/wp-json\/wp\/v2\/posts\/2673\/revisions"}],"wp:attachment":[{"href":"http:\/\/chadorzel.com\/principles\/wp-json\/wp\/v2\/media?parent=2673"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/chadorzel.com\/principles\/wp-json\/wp\/v2\/categories?post=2673"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/chadorzel.com\/principles\/wp-json\/wp\/v2\/tags?post=2673"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}