Thursday, March 02, 2017

Dual purpose dimmer

At the 2017 Summer AAPT meeting in Sacramento Arbor Scientific had a booth in the exhibit hall showing off all their great demos. This Electricity & Magnetism Light Bulb demo caught my eye. It involves an incandescent light bulb with a long loose filament that can be turned on using AC or DC current. While on, a strong neodymium magnet is brought near the bulb with different results depending on the setting. When on DC the filament moves towards one pole of the magnet and away from the other. When on AC the filament vibrates when either pole of the magnet is brought close to it. I wanted one, but the reasonable price was still hard to manage for a once a year demo.

Last year I wanted to show my Conceptual Physics students a working dimmer switch and a simple light bulb. My retired father-in-law made me a self contained box with a dimmer switch and an incandescent bulb:
While shifting equipment around in my room I came across it again while my magnet cabinet was also open. As I recalled the Arbor Scientific demo I thought, "I wonder if...." and grabbed my biggest neodymium magnet. 

With the light bulb on dim so that the filament can be easily seen I moved the magnet close to the bulb. Since my bulb's filament wasn't as long as the one in Arbor Scientific's demo you don't see as much movement but it is vibrating! The second video is easier to see the motion. 

Now I know that my simple demo has a dual purpose and can be used in my current electricity unit and come back in my electromagnetism unit!

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