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seen Apr 7 at 23:07

Apr
7
comment Drying clothes with the sun's heat, without any air
@JoeTaxpayer I thought the answer was a resounding no, but the energy to create a 7 cu feet vacuum against the atmosphere is only 5 watt hour (!). But don't forget you need to keep "replenishing" the vacuum as the water sublimates and pumps are inefficient. Still, it's not obvious that it wouldn't work. It probably is, however, far to expensive to build a vacuum dryer.
Apr
7
comment Why is there a negative sign in front of the optical wave?
Missing $i$ < corrected. Thank you for your other comments. Although, for unsymmetrical signals (I'm speaking generally, not specifically about optics), isn't the sign of the $\omega$ relevant? (Since $exp(jx) = cos(x) + jsin(x)$ and $sin(-x) = - sin(x)$)
Apr
7
comment Why is there a negative sign in front of the optical wave?
I took optics ten years ago. I asked the question because I was reading a paper that wrote $U = U_{o}exp(-j\omega t)$ for vacancy concentration. I'm implementing the paper's model in a program, and that negative sign makes a huge difference (and is welcome). But I can't just add a negative sign in just because I like it. I wanted to know the implications of the negative sign so I can figure out where in my own model I have implicitly assumed my that concentration wave is $U=U_{o}exp(-j\omega t)$
Apr
7
comment Why is there a negative sign in front of the optical wave?
I took optics ten years ago, I forgot a few details in the meantime. So I can't honestly say if there was anything explicitly in the question about direction of travel.
Apr
7
comment Why is there a negative sign in front of the optical wave?
I didn't forget the imaginary unit - it's not a plane wave without it. I remember asking the TA specifically about the negative sign, and being told the negative had to be there.
Feb
23
comment Why isn't temperature measured in Joules?
What I mean is that it's wordy to say T in Joules, in the same manner that it is wordy to give an airplane's airspeed in milimeters/year. eV, an energy unit like Joule, would be better and I would be the first to welcome it so we can start dropping R and k.
Feb
3
comment Where did earth's electric charge come from?
You're not measuring a charge with a voltmeter, you're measuring the potential difference due to a current of charge. The Earth can be neutral and still have ground currents.
Dec
11
comment Computer cooling with dry ice, ideas and question; thermodynamics
@Aron I modified the answer accordingly. However, if we take the question/answer too seriously, it should be re-posted on a chemical engineering exchange. Any extreme cooling will cause condensation, although the ethanol in my solution should absorb quite a bit of water.
Oct
22
comment When a planet is heated through gravitational pull, where is the energy taken from?
I don't think Jupiter would stop rotating. For one, it would violate the conservation of angular momentum. Instead, the Jupiter's rotation and the moons' orbits and rotations will become such that rate of change is zero. Of course, this ignores that Jupiter is a body in the solar system.
Sep
18
comment How do you add temperatures?
It would appear that you were meant to use an interpolation, but I'd ask your colleagues to confirm this (for example there might be a specific type of interpolation that is required)
Jan
21
comment Is it possible to project an image onto water?
why does it "need" to be projected inside the liquid? If you're trying to achieve a 3D effect, you can look into holograms. Also there are techniques to make things appear as if they're projected within the solid. But light will continue going along a straight line unless it encounters a change in n, or a scattering point
Jan
20
comment Overview and doubts about Bloch's theorem and the concept of partial density of states
About the pDOS, lets see if I get this: pDOS is a density of state, meaning that it's a graph showing how many energy states there are at a particular energy. However, to each energy state there corresponds an actual wavefunction (eigenvalue - eigenfunction pair). This wavefunction can be written as a linear sum of spherical functions (the s, p, d). So I can go back to my DOS and plot the four, five points corresponding to how much of each basis function I have. Doing this for all energies, I get continuous lines. Is this right?
Jan
20
comment Overview and doubts about Bloch's theorem and the concept of partial density of states
Continuing about the Bloch's theorem: what if we have a quasicrystal? i.e. an ordered lattice that does not have translation symmetry. Is Bloch's theorem still apply?
Jan
17
comment Do my noodles cook quicker when the water is boiling or when it is just about to boil?
Noodles aren't cooked when they're hot. They're cooked when they're wet - when water has thoroughly diffused into the starch. The cooking time is the time required for water to diffuse into the noodle. Diffusion is greater at high temperatures, and the total water flux into the noodle requires a large contacting surface.
Jan
16
comment What happens to a conducting ring when exposed to an electric field?
But why would they want to travel in the direction opposite the electric field that separated to begin with? I mean, if the field is AC, sure. But with DC?
Jan
16
comment Can an Anti nuclear atom be synthesised so it can neutralise the effect of nuclear atom
I hate to say this (I hate failing students), but you have some fundamental misunderstanding of physics possibly informed by a misreading of mysticism. There is no "nuclear" atom because nuclear is an adjective solely to describe technology. Rather, atoms have a "nucleus", a noun, as a necessary component. "The chain" cannot be neutralized because it is not a noun, but a verb to describe the actions of atoms and neutrons in a critical mass. At best it can be "stopped", by lowering control rods in a reactor, or if a bomb fizzles.
Jan
16
comment What happens to a conducting ring when exposed to an electric field?
If the charges are static, why would they jump (I'm interpreting "jump" to mean that the charges recombine by arcing)? Unless you mean that the charges escape the material to continue travelling along the direction of the E field.
Dec
14
comment Intuitive explanation for why same force applied farther from a hinge causes larger angular acceleration than if applied closer?
I was going to add that force isn't a conserved quantity, and the implications. But you had that covered too.
Dec
11
comment Relation between voltage and current
This is no longer a physics questions, but a biological one. However consider that your muscles probably wouldn't appreciate being yanked in opposite directions at 60 times a second or 10. But the physiological response vs. frequency is not something I can answer.
Dec
11
comment Relation between voltage and current
@xish Of course not. But the external V doesn't matter. The only thing that matters is the voltage drop across your heart, and that DOES depend on your skin's resistance