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Q & A: electromagnetic radiation from metal

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Most recent answer: 06/11/2013
Q:
Electrons(charged particles)when accelerates,radiation is produced.But in metals free electrons collides with each other so they should change their velocities and must accelerate and hence metal should radiate .But it doesn't happen,WHY?
- Ankit (age 17)
Sagar,mp, India
A:

Actually, it does happen. Think of a hot piece of metal, say in an electric heater. You can see it glow. That's the electromagnetic radiation from it. At room temperature, there's almost no visible light emitted, just infrared and lower frequencies. The emitted radiation is then just balanced by absorbed radiation coming from the room.

The part of this story that would not make sense in a classical picture of radiation from accelerating classical charges is the way the frequency spectrum of the emitted light depends on temperature. This problem was the first motivation for Planck's proposal in 1900 that the radiation came in lumps of energy of size E=hf, where f is frequency and h has come to be called Planck's constant. That proposal was the first window into an entirely new way of seeing all the ingredients of the world, quantum mechanics.

Mike W.


(published on 06/11/2013)

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