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Re: [Phys-L] light, doppler effect, particles



On 04/22/2014 08:41 AM, Philip Keller wrote:
Suppose you have a source of light that is just below the threshold
frequency for a given metal surface. You get no photocurrent.

Now suppose the source is approaching at some speed great enough so that
the Doppler effect shifts the frequency to a value above the threshold.
Now you do get photocurrent, yes?

Sure.

Suppose an observer riding with the source uses a beam splitter so that
half the light approaches you and gets Doppler shifted to give you that
photo current but the other half goes to the ride-along observer. He does
not get a photo current...right?

Sure.

I'm not even sure what my question is.

I assume the question is, how do we explain this to somebody
who doesn't already understand it.

Can anyone point me to a
photon-based treatment of the doppler effect?

It's fairly easy to visualize what's going on, by looking at
the spacetime diagrams. This is discussed, with diagrams,
here:

http://www.av8n.com/physics/spacetime-welcome.htm#sec-doppler-1sd

That is a newly-added section. Let me know if you have
questions, comments, or suggestions.

Note: For problems like this, I draw the red-frame diagram
freehand, and then /compute/ the blue-frame diagram. That
way I know all the relationships are correct. I've done this
so many times I can do it in my sleep now.