The Sound of Light

I was recently a guest in a classroom (not at APU) and listened to a fantastic composer and beloved professor tell a room full of eager students that the reason florescent lights buzz when they start to go bad is because some of the light is slowing down, and the frequency of the light is getting so slow that it becomes a sound wave instead of a light wave, which is why the buzz is at 60 Hz.

Nobody in the room contradicted him. Nobody. After about 30-second of dumb disbelief, I protested, and the whole class turned on me as if I were an idiot, daring to argue with this obviously brilliant man.

This brought to mind 3 things:

1. An expert in one area is not an expert in all areas. If you are a teacher, be sure you communicate to your students when you are speaking from your area of expertise, and when you are speaking out of your nether regions. If you are a student, become critically aware  of the difference. 
2. Intellectual authority comes from being right, not from being in a position of authority. Don’t be afraid to challenge professors when they are wrong.
3. In a room full of 20 people, I can’t believe nobody knew enough about light, or sound, or electricity to contradict an obviously absurd assertion. I’m worried that we’ve come to just accept general ignorance about how the world works.

So here’s today’s extra credit question. Help me restore my faith in the world. Without heading to wikipedia or google, with just your general knowledge of physics, what would you have said to the man to demonstrate his error?

10 thoughts on “The Sound of Light

  1. Steve

    To DEMONSTRATE it to a composer, I would ask him when was the last time he noticed a sound wave slow down in a closed room. Did the sound self-detune?

    Or, ask him why a candle or a campfire or a sunset doesn’t have a 60 hz. rumble as it disappears…

  2. Stick

    Unless we’re talking about some crazy relativity theory I’m thinking it’s pretty common knowledge that the speed of light is a constant. But, maybe that’s the issue here.

    I’m curious how he reacted when you called him on it. Did the students jump to your side?

  3. michael Post author

    Stick, he wasn’t talking about the speed of light, he was talking about the frequency of the light wave.

    I pointed out something really obvious, then he changed the subject. I want to wait to see if anyone else figures it out.

  4. Jason Diaz

    It’s the filament vibrating. Didn’t we all build electromagnets in grade school??? Ever see or use an E-Bow on a guitar? Yes, light is energy but if he’s figured out how to convert it directly into air and pressure then let’s give him the Nobel.

  5. Pi

    I like to tell people who don’t have perfect pitch that the 60Hz hum is a Bb so if they ever need to tune to just use that. Eventually this pays off when I’m in the same room as them and someone who has perfect pitch, or a tuner.

  6. michael Post author

    I don’t want to say, because he is actually a very good composer, just not a very good physicist. Or commonsense-kateer.

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