Half a croissant, on a plate, with a sign in front of it saying '50c'
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I recently noticed something interesting*.

My laptop has an aluminium case. When I slide my finger over it, I get a buzzing sensation, but only when the charger is connected. On batteries, no buzz.

This is presumably because of mains hum making it through to the (earthed, I guess) metal case. Perhaps the supply to this wing of the estate isn't well-earthed.

In a quiet room, I can actually hear this buzz, and it is indeed the familiar 50Hz mains frequency. It only happens as I stroke the metal case, and the frequency is independent of the speed of stroking.

I presume, then, that the mains ripple is modulating the friction between my finger than the aluminium, resulting in a slip/stick cycle at 50Hz.

So. If a similar voltage ripple were applied to a thin, sonorous metal sheet, I'd expect to be able to make a somewhat louder 50Hz hum by stroking it.

But why stop at 50Hz? An array of metal sheets, each fed with a modest voltage at a different frequency, would be a musical instrument slightly akin to a glass harp.

[*Six out of ten customers agree]

MaxwellBuchanan, Mar 23 2014

Theremin http://en.wikipedia.org/wiki/Theremin
Go wireless [Spacecoyote, Mar 24 2014]

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       I always pictured you sitting in a wingchair stroking a long-haired white cat.
AusCan531, Mar 23 2014

       You could compose a very interesting avant-garde binary composition in the style of that very slow organ piece. You have to fly across the Atlantic in between dissimilar notes.
pocmloc, Mar 24 2014

       //I always pictured you sitting in a wingchair stroking a long-haired white cat.//   

       Yes, often, but I seldom plug the cat into the charger.
MaxwellBuchanan, Mar 24 2014


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