Physics Phriday: Singing Tesla Coils

These tesla coils are amazing!  The music is made by the sparks you see.

This video is of a band named Arc Attack (with a robot drummer) who build and use these tesla coils as their instruments.

Here’s a similar setup (looks like it’s in someone’s driveway) playing Sweet Home Alabama.

Here’s an excellent interview with Arc Attack explaining how these tesla coils work, and how the band makes them.  It’s worth watching the whole thing, particularly for some electromagnetic destruction at the end.

The Physics of Bleach

Ever wondered what would happen if you poured bleach into coke? (DON’T TRY THIS AT HOME!!!!!!)

Bleach contains highly reactive molecules, like the loosely-bound sodium hypochlorite that functions as the active ingredient in standard chlorine bleaches like Clorox. When it’s poured onto a stain, (or into a glass of coke) the chlorine-oxygen group sticks to the pigment molecules, bending them out of shape and changing which wavelengths excite their electrons. Like a bent radio antenna, those molecules can no longer absorb or reflect the electromagnetic energy they were previously sensitive to, and the photons pass on through them. When we bleach a ketchup stain, it may look like it comes out of the fabric, but the reality is that the lycopene molecules are still there—they’ve just been rendered invisible by all the extra atoms that have been stuck onto them!

Calculating the Speed of Light

Here is an interesting post explaining how to calculate the speed of light.  Some of the formulas are AP physics level, but the concepts are understandable even if you don’t know exactly how the formulas work.

If you plug in the actual numerical values for the vacuum permittivity and permeability, it works out to 299,792,400 meters per second—precisely the speed of light!

So what does this mean? … [I]t gives us a clue as to why the speed of light in vacuum is what it is; it’s the speed where electric and magnetic forces balance out to create a stable electromagnetic wave packet that can travel indefinitely. Any slower and the photon would come undone, just as the wires would be pushed apart by the electric repulsion. Any faster, and the magnetism would overcome that repulsion and draw them together, collapsing the system. With nothing more than high school-level math, it’s easy to show that the speed of light in a medium (or in the vacuum of space) inevitably arises as a consequence of that medium’s electric permittivity and magnetic permeability.