This looks like a simple application of qv x B. The thin filament carries an increasing current in the earth's magnetic field (or perhaps some other stronger external field). This will result in a 60 Hz vibration.
I do a similar demo using a light bulb with a long looping unsupported filament and a small permanent magnet. This filament can vibrate back and forth about 1 cm.
Tim
------ Original message------
From: Derek McKenzie
Date: Tue, Dec 26, 2017 2:47 PM
To: phys-l@phys-l.org;
Cc:
Subject:[Phys-L] On the source of vibration of a heating filament
After coming across a lovely slow motion image of a tungsten filament
heating up (link below), I was quick to explain it in a way which I now
believe was silly (thanks to a couple of readers who may well be on this
list), and I'm looking for your input.
As the filament heats up, it begins to vibrate in a gentle but
observable way, and I'm wondering how best to explain the vibrations.
(My initial assumption of thermal excitation of the constituent atoms
appears to be wrong for more than one reason, but I'd be happy to hear a
thorough critique of it here.)
Derek McKenzie
PhysicsFootnotes.com
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