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Apr
27
comment Would it be efficient to run a solar panel with laser?
Solar cells can have monochromatic efficiencies approaching 80%. Look into power over fibre.
Apr
25
comment Is thermal/heat energy the same thing as internal energy?
In a heat pump heat flows from cold to hot. This definition is not general enough. Heat is just a transfer of energy and entropy.
Dec
22
comment Simplest form of thermodynamic cooling equation?
I think a rate equation approach would be best for this problem.
Dec
10
comment Fluorescent Lights Held Near A Tesla Coil
My guess is that a rapidly time altering electric fields causes collisions between the gas molecules in the tube and because the tube is at low pressure they can reach high velocities. When collisions occur, charges can be exchanged, they relax to ground the ground state by emitting UV light (in the example of Mercury vapour). The UV excites the inner phosphor coating on the tube and you see the tube light in regions where the vapour emits most i.e. close to the source of the AC field. Interested in hearing a full explanation.
Dec
8
comment Why doesn't power generated by thermal radiation violate Carnot's theorem?
Yes, photovoltaics convert 'heat' in the form of optical radiation directly to electricity and because the solar cell has a constant temperature I can see were confusion might arise. Endoreversible thermodynamic provides a nice way of viewing this problem: the solar cell is connected to two temperature reservoirs via resistors that introduce irreversibilities (look up the work of DeVos). In photovoltaics the gradient across the Carnot engine is a chemical potential and not thermal in nature. But this gradient is ultimately driven by the temperature difference between the sun and the Earth.
Dec
8
comment Why doesn't power generated by thermal radiation violate Carnot's theorem?
The efficiency of the Carnot engine is a function of the temperature gradient across the engine. By definition it requires reservoirs at different temperatures. Can you ask a specific question/concept that you are finding difficult?
Nov
13
comment White Laser Light
Supercontinuum lasers are not monochromatic.
Nov
3
comment Tension of a string, based on Hz, string-weight and string-length
Use the equation for tension here to work out the value physics.stackexchange.com/questions/202454/…
Nov
1
comment Role of Chemical potential in Bosonic gas
The gist is (for a photon gas at least) that photons don't interact with each other thus we generally say they have zero chemical potential. However if a photon gas interacts with Fermions (for example, electrons and holes in a semiconductor) then the chemical potential of the photon gas becomes the same as the chemical potential of the electrons and holes. I'm afraid that I can't state that in more general statistical mechanics terminology and my knowledge is specific to photons. But it's an interesting question, hope you get an answer.
Oct
28
comment Energy magnetization in the presence of temperature and chemical potential gradient
Landauer equation might get you some part of the way. It deals with nanoscale transport due to differences in distribution functions.
Oct
20
comment Why do people put exponentials there
Maybe also something about differentiability?
Oct
16
comment Reduce integration over crystal to integration over unit cell
Very well posed question.
Oct
7
comment Device design regarding recombination mechanisms
Just looking at the electron rates. You can write a similar equation for holes.
Sep
27
comment Brightness of light sources
In radiative transfer brightness is defined as the specific intensity per solid angle. Metrics for light can be so confusing and numerous.
Sep
26
comment How to measure blue light at home?
Well you need to look at the transmission graphs and select a filter which has very high values in 400 to 470 region. But a word of warning, you might have to use a second filter to block out the IR because the blue filter tend to transmit again towards the red end of the spectrum. So pick a short wave pass that lets blue though and combine it with a red-IR block.
Sep
26
comment How to measure blue light at home?
If you get the transmission spectrum of the filter in the range of interest you could do that. Blue-pass red-green-IR block are hard to find.
Sep
26
comment How can photons/particles/objects/things be massless?
Answered here, physics.stackexchange.com/q/2229
Sep
25
comment How can metals absorb light?
"...which makes the metal transparent"
Sep
24
comment Intuitive way to think about discrete energy levels
They are simply the energy associated with a standing wave probability distribution. What's not intuitive about that. But serious read about the Copenhagen interpretation.
Sep
23
comment Single Narrow Sunbeam
Could be be a reflection from the curved bonnet (hood) of your car that you are seeing projected onto the windscreen (windshield) to make it look like a sunbeam that curves? Light doesn't curve in the atmosphere (no smart arse graded refractive index comments please).