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18

If it is incandescent, then temperature to some extent, but mostly the light of the wrong color gets filtered out by the colored glass bulb. If it is something like electric discharge lamps, then it is the gas used (eg sodium vapor) or the phosphors coating the inside of the tube converting UV to visible light/color (eg mercury vapor UV emissions). With LED ...


10

For starters, even though you don't say it explicitly, I'm going to assume you're talking about incandescent light bulbs (since you mention filaments in your question). There are many other types of light bulbs, such as compact fluorescent lamp (CFL) or light-emiting diodes (LED). Each of these different types work somewhat differently, and as a result, ...


7

I am going to answer this on the assumption you are talking about an incandescent lamp. A tungsten filament is heated by the current flowing through it, and starts to behave like a black body radiator. Now a tungsten filament is not a perfect black body: the emissivity is a function of wavelength and has been characterized (see ...


4

Yes, the probability for the electron to be found inside the nucleus is, for some atomic orbitals, non-zero. However, you must recall that these orbitals usually assume a point charge for the nucleus, and so they may not be a valid when you "zoom in" to the nucleus. Nevertheless, there's nothing inherently wrong with the electron being where the proton is - ...


2

AdS black holes exist in various dimensions, $p=3$ is not the only choice. The parameter can take on values above or below $3$. One famous example is the three-dimensional BTZ black hole, and higher dimensional ones are also frequently used in the correspondence. Furthermore, I think there is a misunderstanding on the concept of a "gravity dual". The metric ...


2

Since gas molecules are affected by gravity, wouldn't that make gas molecules at higher than average elevation slower (at the top of their ballistic parabola) and thus colder than air molecules accelerating to the ground? In non-relativistic theory no, because in thermodynamic equilibrium temperature has to be the same everywhere. The slowing down does ...


2

This is a very old question, but none of the answers fully address the question. I'll frame my answer in terms of answers to a series of questions: How much does temperature vary with altitude? Why does pressure vary with altitude? Why does temperature vary with altitude? What about the second law of thermodynamics? Why is the Tibetan Plateau so cold so ...


2

Because what you are doing is a flow process, with mass inflow and no mass outflow, you need to use the thermodynamic equation: $dU_{cv}={m_{in}d}{H}_{in}-{m_{out}d}H_{out}+\delta Q-\delta W_{shaft}$ If you insulate your air cylinder well enough, $\delta Q = 0$. Assuming that your air cylinder does not deform, $\delta W = 0$. Since you are filling your ...


2

I believe the confusion is that you believe pressure will always increase as temperature increases. This is only the case in a closed environment such as inside the tire. In an environment such as the atmosphere which is, essentially, in an unconfined environment, the density will decrease with temperature as well. This does not happen inside of a closed ...


2

The problem with the Boltzmann definition is, as you have neatly shown, that its usefulness depends on the assumption that your system is in equilibrium with its surroundings. Without first assuming equilibrium and subsequently setting the temperatures as equal, one cannot show that the Boltzmann entropy satisfies the First Law and hence meaningfully define ...


2

A rough estimate can be obtained as follows. At the extremely high intensity radiation the temperature will be determined by radiative equilibrium. Now, in the case of purely radiative equilibrium, an object that receives the solar radiation that reaches the Earth would reach the a similar temperature as the lunar surface. At the equator, the maximum ...


1

This isn't a complete answer, but John Baez gave a pretty good treatment of this in a series of blog posts (part 1, part 2, part 3, part 4; arXiv paper with some more stuff). Basically, he defines what he calls the "quantropy", which is just the classical entropy formula with $\beta$ replaced by $-i/\hbar$ and the energy replaced with the action. (Note ...


1

There's a tiny trace of helium in air, about 5 parts in a million. The pressure isn't high enough for it to freeze no matter how cold it gets


1

The lens works because it takes all the sunlight falling on its area, $A_1$, and focuses it onto a small spot $A_2$. The intensity in the spot is the intensity of the sunlight multiplied by $A_1/A_2$. Exactly the same applies to a mirror. So provided your mirror has the same cross sectional area as the lens, and provided it can focus the light as ...


1

There are, by my count, 33 other official weather observation stations within Sydney. Here's a map: With regard to the Sydney - Observation Hills (Station ID 066062) station -- That freeway didn't exist when the station was built. How could it? That station dates back to 1858. The station was moved 150 meters to its current location in 1917. That tiny ...



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