Metals are Shiny

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metals_are_shiny

“Metals are shiny.” That’s one of my favourite punchlines to end a class on electromagnetism with, and that’s what I did today. I just love bringing up a bit of everyday physics as a striking consequence of two hours worth of development on the board, and this is a good one for that. I hope the class enjoyed it as much as I did! (Basically, as you can’t see in the snapshot of my notes in the photo, those expressions are results of a computation of the scattering of light from an insulator like air into a medium that conducts. There’s a reflected amount, on the left (there should be an equal sign… I missed it off) and there’s a bit that goes through, the transmitted bit, on the right. For a good conductor, like a classical metal, that parameter beta gets really large, and as a result the reflected part of a wave dominates over the transmitted part, meaning that the thing is highly reflective. Metals are shiny… No? Maybe it’s the way I tell ’em.)

-cvj

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28 Responses to Metals are Shiny

  1. Robert says:
    October 7, 2015 at 2:27 am

    Another history of science factoid is that the phlogiston theory (p. is the stuff in a material that comes out when you burn it. It got into trouble when having better scales showed it had to have negative mass and was then replaced by the oxygen theory) was to some degree able to explain the shininess as well: It is the phlogiston that is shiny. Oxygen, the competing theory (or paradigm in Kuhn’s words) had nothing to say about shininess and declared this question as unscientific and it stayed like that until the days of quantum mechanics. This is the main counter example that theories that succeed others are always able to explain a superset of phenomena.

  2. Mark Peifer says:
    October 6, 2015 at 6:42 am

    If you had been my high school physics teacher, things might have ended up differently…… (though I do love Biology)

  3. Robert says:
    October 6, 2015 at 6:31 am

    A few days ago, my 4yo asked over dinner why metals (gold in his example) are shiny. Maybe my explanation was a bit too long but he followed it for quite a while. But I did not use your approach, rather I started introducing him to atomic theory (what happens when you keep splitting a piece of chocolate, does it stay chocolate?), then explained that some of the “atomic” parts are electrons and that those can move around freely in a metal. And that those prevent light from entering since they vibrate in the (electromagnetic, I did not use that word) wave.