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 Mar 15 awarded Nice Answer Oct 13 comment Non-ideal black body's thermal radiation? @BowlOfRed That being said, if I shine 5 micron light on my object, the object will absorb that 5 micron light strongly and begin to warm up. As it warms, its output at 10 microns will increase. However, this scenario violates the premise that the object is in thermodynamic equilibrium; that assumption dictates that certain relative amounts of each wavelength are falling on the object. If the incident radiation field is out of thermodynamic equilibrium with the object, then the object will gradually change temperature until it has regained equilibrium with its environment. Oct 13 comment Non-ideal black body's thermal radiation? @BowlOfRed To elaborate, suppose I have a material that is a strong absorber at 5 microns and a weak absorber at 10 microns. I might suppose that energy absorbed at 5 microns might be strongly emitted at 10 microns; this is not the case. The strong 5 micron absorption corresponds to a strong 5 micron emission, while the weak 10 micron absorption corresponds to a weak 10 micron emission. Oct 13 comment Non-ideal black body's thermal radiation? @KarlDamgaardAsmussen You are correct. A perfectly mirrored body will not emit any thermal radiation; this is why a polished silver surface is used in dewars (thermoses). A vacuum between the inner and outer layer is used to prevent conductive and convective losses, but the reflective surface prevents transmissive or absorptive radiative losses. Oct 13 comment Non-ideal black body's thermal radiation? @BowlOfRed What it means is that, for a body in thermodynamic equilibrium, $\epsilon(\lambda) = \alpha(\lambda)$ holds for all lambda. One might expect that it would be good enough for $\sum_\lambda \epsilon(\lambda) = \sum_\lambda \alpha(\lambda)$, but the equivalence is stronger than this; it holds for all wavelengths individually, not just for the collection of wavelengths. Oct 13 revised Non-ideal black body's thermal radiation? Clarity. Oct 13 answered Non-ideal black body's thermal radiation? Oct 7 comment How fast does an ice cube melt in a microwave? It seems that the link should be to page 184 of books.google.com/… Oct 7 comment How fast does an ice cube melt in a microwave? The salt water bit comes from the same source all these images are from. Oct 7 revised How fast does an ice cube melt in a microwave? Reverted correction due to erroneous interpretation of graph. Oct 7 suggested approved edit on How fast does an ice cube melt in a microwave? Oct 7 comment How fast does an ice cube melt in a microwave? Sorry for making my comment; your initial interpretation was correct. I had seen the arrows as idicating the line at 0C, rather than illustrating the progression from 0 to 100. Oct 1 comment How fast does an ice cube melt in a microwave? The figure is somewhat unclear, but it illustrates that cold water heats up more slowly than hot water for 2.45 GHz microwaves. Sep 7 awarded Yearling Feb 4 comment When can one write $a=v \cdot dv/dx$? This implies that a function must be invertible in order to have a well defined spatial derivative, but that isn't true. Many functions must restrict their inverses to a particular domain, while still having well defined derivatives outside that domain (e.g., sine and cosine). Even if the velocity cannot be expressed analytically as a function of position, the spatial derivative may still be well defined, and thus the OPs original integral may still be valid, even if no clean expression for v(x) can be found. Feb 3 comment Do wide-angle videos make the first-person view seem slower than perceived in real life? @AndrewCheong The transform that attempts to achieve what you are looking for is the stereographic transform. However, since few fisheye lenses use this mapping, you may find that the transform from equisolid-angle to stereographic projections remove too much scene or diminish image quality to an unacceptable level near the edges. Feb 3 comment Do wide-angle videos make the first-person view seem slower than perceived in real life? @AlistairAdams I've amended the answer to address the difference in edge effects between normal and fisheye lenses. Feb 3 revised Do wide-angle videos make the first-person view seem slower than perceived in real life? Typo fix. Sep 30 awarded Explainer Sep 7 awarded Yearling