Activity

Transcription follows. [Apparently the site I use started adding time stamps and its guess as to who’s speaking.]

00:00:07 [Speaker 2]
Good afternoon.
00:00:09 [Speaker 2]
Thank you for continuing with our derivation of the black body radiation formula and the ultraviolet catastrophe.
00:00:20 [Speaker 2]
So having gone on a long digression,…[Read more]

Transcription:
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So last time we left off in the main lecture, we had just introduced the concept of entropy, how it’s the logarithm of the multiplicity. Long numbers turn the very large numbers of multiplicity into merely large numbers. 10 to the twenty third is supposed to 10 to the power of 10 to the 23, and it makes…[Read more]

I think I just realized something else that addresses a big part of my confusion. I think it was more-or-less stated in the talks, but I wasn’t getting it.

When we discuss the k-vector, where each n must be at least 1, we are talking about the composite standing wave (the superposition of individual waves), and only this wave, correct?

I was…[Read more]

Based on this image from Stephan’s slide, I’ve concluded I’ve had a fundamental misunderstanding of the waves we’ve discussed.

Both the left and right images show a wave that exists in 2-D. The left image uses a 3rd dimension to show the value of the wave in each 2-D location, and the image on the right uses color.

To truly picture the 3-D…[Read more]

Apparently I just described what the slides show 3 slides later, which the caption says is a 2-D version.
This raises more questions for me.

Transcript:

And then next, you asked about, black bodies. Uh-huh. So okay. So the there’s the general principle that if a object absorbs a particular wavelength, it emits it also naturally by this process. But if it body.

Yeah. Anybody. See, the what we the reason why we talk about black bodies is that they’re an idealized object that would…[Read more]

I’m glad it’s helpful!

Thank you @john for that transcript! I was traveling during the last meeting and wanted to review what had been discussed. I almost never watch videos as it’s hard for me to process and engage with content in that form. It’s significantly easier for me to read though, so having the transcript above to review the last meeting (and track which slide…[Read more]

Slide 18: “Macroscopic systems in thermal equilibrium are always in a state
of maximum entropy.”

At this point should we understand why systems NOT in thermal equilibrium are not necessarily in a state of maximum entropy?

Regarding entropy:

Suppose I drop 4 dimes on a square meter board. (Grant some way of doing it such that their positions are random; any coin on a boundary is counted in the region that has more of its mass.) Am I thinking about the following scenarios correctly?

1. Considering the left and right halves of the board, there are 2^N = 16…

[Read more]

More questions on slide 11:

1. can I see an illustration of a wave with a k vector of, say (1, 2, 3)?
2. does the k vector determine the wave’s frequency?
3. if (2)’s answer is yes, isn’t the wave’s energy determined by its k vector?
4. if (3)’s answer is yes, why do we speak of the average energy of a wave with a certain k vector?

Let’s see how much of slide 11 I’m understanding.

Suppose we have a blackbody of 1m on each side.

Suppose a photon is emitted from the middle of one of the “x” sides, and is absorbed in the middle of the opposite “x” side, so its path has no component along the y or z dimensions. Also suppose its wavelength is 1m.

1) Is it correct that its…[Read more]

Only when reviewing slide 11 did it occur to me:
We’re to think of these black boxes as cavities, emitting light from any/all points of the walls inside the box, to be absorbed at some other point inside the box, correct?

The image on slide 6 predisposed me to thinking of these boxes emitting externally.