Recent content by Philip Koeck

You can do it with 2 lenses. The first has to have 10 times the focal length of the second, for example 100 mm and 10 mm. Place them so they share a focal point.

Thanks! That's a great proof.

I want to consider all possible reversible cycles that consist of an isothermal expansion at TH and an isothermal compression at TC. The other two processes can be isochoric, isobaric, adiabatic or anything else, but they should never leave the temperature range between the two isotherms. I also...

I would agree with you.

I think you have it. With the bowl it's just a bit more complicated since the surface area of the mercury in the bowl is different from the cross-sectional area of the tube, but the balance of forces acting on the column of mercury in the tube is exactly the same. It's true that pressure acts...

I think it might be easier to discuss if you refer to the picture below since you can clearly see which forces are balanced. Give it a try.

Think of the force pushing the mercury up into the tube and the force pulling it down. I think it's simpler with the situation in the picture above.

That wouldn't work for me, I'm afraid.

Actually I wasn't asking about real objects. My question was how we can know that a formula that was derived for the radiation emitted from a hole in a cavity is also valid for a hypothetical, solid black body, for example a lump of metal painted with ideal black paint. My conceptual problem is...

I was thinking of an ideal black body, not necessarily anything that could be realized. My main conceptual problem is how to apply a statement about EM-waves in a cavity to a situation where EM-waves are emitted from the surface of a solid, no matter what the solid is made of. Derivations that...

I understand that Planck's law is derived for a cavity with a hole in it. I haven't found a clear argument that the same result and all results that follow from it also apply to solid surfaces that are black. Can anybody point me to a text that shows this?

Did you get any feedback on your result or even a solution?

I would say A - (N-1) 4π r2 is the area available to any given disk. Is this a model for something discussed in a textbook? I assume you got this exercise from a book, or?

I wouldn't say "large N". N should only be large compared to 1, but not too large.

This doesn't look right to me. The dimensions are inconsistent. Now I see. You probably mean A = (L - 2r)2.