All Questions

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Can condensation occur in a unsaturated vapor?

Consider that a gas mixture of vapor$+$inert gas is unsaturated with concentration (or molar fraction) $x_\infty$ far from a clear, cooled substrate of temperature $T_\text{w}$, i.e. ...
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Is the visible light from “red-hot glass” at least close to Blackbody Radiation?

In this really nice answer @RobJeffries explains the difference between the ideas of Thermal Radiation and Blackbody Radiation in the context of a source which may be in thermal equilibrium, but who's ...
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How can excite a semiconductor to make a photon just by heat in room temperature?

I want to know if a semiconductor in room temperature can excite by heat, producing photon, without any other source of energy?
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What factors will make Earth re-rotate again if it stopped? [on hold]

"What will happen if Earth stopped rotating?" have been answered multiple times with a lot of informative and interesting answers. Continuing this hypothetical question, I have another one in mind. ...
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What is the Relationship Between Poisson Brackets and Additive Integrals of Motion?

Question in the title: what is the relationship, if any, between Poisson brackets and additive integrals of motion? Context: Is there anything we can say about additive integrals of motion in ...
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Slowly Varying Functions for Adiabatic Invariants - The Same as Karamata's?

In section 49 (and 50) of Landau and Lifschitz's "Classical Mechanics", adiabatic invariants are discussed, which are related to functions which vary adiabatically or "slowly" with time. Admittedly ...
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How does pressure change over time in an open box?

Imagine that you have a 1 cubic meter metal box with two 20 mm diameter holes. One of them is connected to an air-compressor that constantly pressurizes the inside of cube. Let's say 5 atm. The other ...
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Do gases have phonons?

A phonon is a quantized unit of sound; they are encountered when quantizing lattice vibrations in solids. Now, even an ideal gas supports sound waves, but in such a case, interactions between atoms ...
1k views

Same photon or different photon?

Consider a typical optical focusing system: A small light source, then a collimating lens, then a focussing lens, and then a detector (e.g. CCD). Assume that source intensity is so low that only one ...
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What is a good mathematical introduction to QFT [duplicate]

I've noticed that, any time I try to pick up Peskin and Schroeder, the main stumbling block it the leap in mathematical constructs from QM. Is there a good textbook that could teach me some of the ...
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Gimbal Lock: why is it a problem?

I was watching this video http://www.youtube.com/watch?v=rrUCBOlJdt4 about the gimbal lock problem. I understood that during rotations it could happen that one DOF disappear. Looking at the middle ...
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Why is standing still easier than walking?

Both the works basically push force into the ground.So why does walking require more work?
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Frequency of other light in white light

I have this question in mind because I read that the frequency of light depends only on the source of light. If we consider a source of white light then it emits light of different colours also. Then ...
16 views

Relativistic Mass and Potential Energy

In the chapter 16–4 of the Feynman Lectures, Feynman employs a thought experiment to explain why "if two particles come together and produce potential or any other form of energy; if the pieces are ...
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Counting states

Assume we have 6 particles, 3 with spin $\frac{1}{2}$ and another 3 with spin 1. The particles are distinguishable. The energy of a spin s is $\epsilon=-s \mu H$. How many energy states the system ...
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Do all solid objects emit visible light?

Are there solid objects that do not emit visible light? To my limited and humble knowledge, creating such an object would require us to "only" shift the spectrum of emitted radiation. Is it possible? ...
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Where is the zero electric potential energy point?

Does the point of the electric potential energy of zero is defined by human or dominated by the indefinite integral of the electric force?
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Pole and Barn Paradox w/ Spacetime Interval

I'm having trouble with a pole and barn paradox problem. The problem is as follows: A pole vaulter is running with a pole at $v=\frac{\sqrt3}{2}c$. Her pole has a proper length of $L$. She runs ...
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Equivalent of the word “Attitude” for the other three DoFs [on hold]

When discussing the physical state of a thing (e.g. a satellite), you can refer to its attitude state (which, to me, consists of its attitude and its derivatives/rates) and its.... non-attitude state ...
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Finding the speed of electrons in a magnetic field

So I'm trying to solve this problem in which an electron beam is "drawing a picture" on a TV screen. The electrons are accelerated to a voltage of $3 kV$ by wire coils and are then directed to ...
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How does Modified Newtonian Dynamics (MOND) violate Newton's laws?

I have read some articles on MOND which indicate that a modification of gravity violate Newton's third law, but I don't know how exactly that works. I do know that if Newtonian acceleration is smaller ...
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How is it guaranteed that electrical connections could be made without destroying a diode laser?

A diode laser is a tiny diode and requires a microscope to see it. Since a laser generates a good amount of heat, the diode should be destroyed with the produced heat. But it does not happen. but why ...
22 views

Electron velocity in hydrogen

I was speculating over the feasibility of myon catalysed fusion. Somehow I drifted away from that a little, and I was wondering if one can find a quantum-mechanical expression for the velocity of an ...
58 views

Why is carbon not a semiconductor?

As opposed to silicon and germanium (or tin and lead), carbon is not a semiconductor --even though, they are in the same group. More interestingly, diamond (which is carbon) seems to be a good ...
38 views

Understanding potential energy

I am self-studying the classical mechanics using the book by Taylor, and I have a question about the potential energy. The book (pg 111) says: If all forces on an object are conservative, we can ...
33 views

Quantum teleportation and macroscopic objects

Purely speculative. If not allowed, I'll delete. If quantum teleportation was scalable to macroscopic objects, I assume it would require an amount of matter at the destination, equal to the amount of ...
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What wavelengths of electromagnetic radiation are emitted by the LH2/LOX reaction?

Rocket engines such as the Rocketdyne Rocket System 68 and the Space Shuttle Main Engine use liquid hydrogen and liquid oxygen as propellants. The exhaust from this type of engine is notable in ...
23 views

Annihilation operator in harmonic oscillator

In Wikipedia's QHO page there is a moment when the following is stated: I don't know why "the ground state in the position representation is determined by $a|0\rangle=0$". I would say that the ...
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How to calculate heat emitted and the range

If I have a source of heat and I know it's surface temperature and size (suppose there are no barriers, only vacuum) can I then calculate the length to which the heat will be felt, and create a graph ...
22 views

Conservation of Komar Mass

The definition of Komar Mass in GR is associated with one asymptotically flat end. However, a hypersurface may contain more than one end, such as the spacelike Einstein Rosen bridge in Kruskal ...
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Colliding beams vs static target

In this problem I need to find the threshold energy of a positron-electron collision that creates a Z boson (the reverse of the following picture; Z mass 92 GeV) in two distinct cases: collision ring ...
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Antiunitary operators in the tenfold way

In the classification of free fermion systems in condensed matter, physicists usually divide the systems into ten symmetry classes, first discovered by Altland and Zirnbauer. In their classification, ...
41 views

Does visible light heat things up?

During a sunny day the walls of my house warm up (no surprise). My question: how much of this warming up (if any) comes from visible light? I associate infrared with thermal energy. If my house was ...
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Where can a particle be found in a wavefunction [on hold]

Let me rephrase my question. Consider the 3d wave packet of a free particle moving along the x-axis. The wave packet will have components in the y and z dimensions as well as the x dimension. What ...
33 views

Surface brightness

I have to compute the surface brightness as a function of the radius from the following set of data: {right ascension ($\alpha$), declination ($\delta$), magnitude (m)}. I also know the center of the ...