Worksheet 2: FAQ
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(QUESTION)
For the first part, you want us to create something close to the Compton effect equation classically.
I don't know how to start this. The book said it couldn't be explained classically. Could you please
define what classically equations we can use, and/or how to mentally visualize the classical
interpretation? What I understand is that the classical interpretation has light coming in at
speed (lambda*v)= c. The EM field then causes the electron to vibrate at the same frequency of
the light. What then? Classically, I would have thought the electron would re-radiate a
distribution of very low-frequency EM waves as it slows down (since the energy wouldn't be quantized).
For the second part. I don't fully understand your question. I know that the work function is
essentially a potential well. If the photon has less energy, the electron is excited a little
and then drops to a lower energy level and emits a lower frequency photon. If it has more, the
electron leaves with the excess energy as kinetic energy. By "emitter" and "collector" do you
mean emitting or collecting photons? And what do you mean by Vstop (”Vstart) (Vcantwork)? Does
v stand for velocity of emitted electron? Is it potential energy? If so could you please
elaborate on what it means/is asking about some potential energy?
Thank you,
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(RESPONSE)
Hey,
Try treating it as a collision where momentum and kinetic energy are conserved.
The incoming photon will have kinetic energy of hc/lambda and momentum hc/lambda.
After the collision there will be a photon with new kinetc energy and momentum in a certain
direction.
After the collision the electron will its own have kinetic energy and momentum in a certain
direction.
Then you use the conservation of energy and momentum like you would for any collision
problem.
Emitter - photons shine on this and electrons are potentially emitted
Collector - the piece of metal where energetic enough electrons are collected
Vstop - stopping potential
Vstart- can you reverse Vstop and get electrons flowing?
Vcant- no way you'll get that collector gathering electrons at a reasonable (few volts)
voltage.
Let me know if this helps,
w.j.
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(QUESTION)
Subject: Compton derivation
When deriving the Compton formula, I'm not sure where the variables vo and vf should come from. Do you have any hints?
Also, what are we supposed to use for the momentum of a photon? Is it p = h/Lambda?
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(RESPONSE)
vo and vf are initial and final frequencies.
You are correct about the momentum.
recall wavelength*frequency = c
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