1
vote
1answer
54 views

Why don't we need to normalize wavefunction to find probability distribution?

Consider an unormalized wavefunction of a rotor at $t = 0$, a combination of $n=0$ and $n=2$ states: $$\psi(\phi) = 3 - 2 \cos (2\phi).$$ Find the probability distribution in angle. The ...
1
vote
2answers
975 views

Finding max height of a mass lanuched by a spring?

I have the following problem on my homework. The actual problem has numbers, but I figure using symbolic notation will help me understand the concept in the long run. A block of mass $M$ is launched ...
0
votes
0answers
8 views

Any recommendations for self-studying physics? [duplicate]

I'm new to this forum so I hope this post falls under the guidelines of what's acceptable. I'm currently finishing my grade 11 year of high school and I have hopes of attending one of the prestigious ...
0
votes
1answer
33 views

Understanding Poynting's Theorem intuitively

I understand that, broadly speaking, Poynting's theorem is a statement of conservation of energy. Energy density of a volume of current and charge decreases proportionally to work done on charges ...
1
vote
1answer
63 views

Hydrogen atom: potential well and orbit radii

I happened to open up an old solid-state electronics book by Sah, and in it he says: "it is evident that the electron orbit radius is half the well radius at the energy level En" The orbit radius is ...
0
votes
3answers
241 views

Mass or no mass?

Do all forms of energy have a mass? We know by $E=mc^2$ that mass and energy are directly proportional, but there are massless forms of energy such as electro-magnetic waves. I am also told that there ...
0
votes
1answer
27 views

Small Animal Terminal Velocity

I recently saw a cat fall probably 100 feet like in this video Cat Falls. It seemed as if the cat reached terminal velocity by the time it hit. Does this mean that cats (and other small animals) could ...
0
votes
1answer
33 views

consequences of universe in which second law of thermodynamics does not hold [on hold]

What happen if second law of thermodynamics does not there for governing every day processes.Can universe exist and evolve if second law of thermodynamics does not exist ,in first place?
4
votes
1answer
141 views

Vibrational anharmonic coupling and noise-induced spontaneous symmetry breaking in a hexagonal finite mechanical lattice

Happy holidays, everyone! The following is part question, part visual gallery, and part classical mechanics problem. Inspired by snow over the weekend I began simulating the vibrations of the ...
0
votes
2answers
61 views

Cylindrical Fresnel Lens Focus Problem

How to focus beam from the fresnel lens on a flat surface. In my case, instead of producing the light beam, I am receiving the light beam. So, the beam comes from the right and then focuses at a ...
5
votes
1answer
53 views

What do the latest FERMI results say about dark matter?

There was an announcement at a recent UCLA symposium on dark matter by the FERMI collaboration which hints at some evidence of dark matter. The results aren't yet published, but the symposium news ...
1
vote
1answer
109 views

How to calculate the amout of time for oil to get out from a pneumatic cylinder?

I have a system. You can assume it is just a 1" diameter steel pneumatic cylinder (1 foot long). Assume we ignore the bore size issue at this point. One chamber is filled up by oil (6" of volume), ...
2
votes
1answer
30 views

Dipole matrix elements through parity argument

I am trying to find the following dipole moment matrix element $(|n,\ell,m\rangle)$. $$e\langle1,0,0|\vec r|2,0,0\rangle$$ I believe that I can say this matrix element is zero because of parity. The ...
4
votes
1answer
49 views

Some question about symplectic transformation

I read Arnold's book Mathematical Methods of Classical Mechanics and come across with three problems in page 229. 1.Let $\lambda$ and $\bar{\lambda}$ be simple (multiplicity 1) eigenvalues of a ...
6
votes
0answers
106 views

Why aren't we surrounded by Black holes?

The Bekenstein bound is a limit to the amount of entropy a thermodynamical system can have. The bound is given by the following expression: \begin{equation} S \leq \frac{2 \pi k R E}{\hbar c} ...
1
vote
2answers
30 views

Can matter be converted to information?

I know that matter can be converted to energy through E=mc^2. I also know that engery can be and has been converted to information through Landauer's principle (with Maxwell's demons). Does this ...
2
votes
3answers
189 views

What does the Pauli Exclusion Principle say about a superposition of spin states?

Suppose we have an atom. It is commonly said that because of the PEP, two electrons can't be in the ground state unless they have opposite spins, because no two electrons can have the same ...
0
votes
1answer
39 views

Jet taking off from an aircraft carrier

If a jet takes off from an aircraft carrier, should it not already be traveling at the speed of the carrier. Also, does the jet require more energy to get off the carrier than from a stationary base? ...
5
votes
1answer
90 views

3D coherence of light speckles- difference between Airy and gaussian speckles

In this article, http://www.dfm.uninsubria.it/laboferri/web_page/articoli_pdf/PRA_2009-Magatti-Three_dimensional_coherence_of_light_speckles-experiment.pdf, the 3D-coherence properties of light ...
0
votes
1answer
30 views

Thermodynamic entropy vs. quantum mechanical entropy

Is there a fundamental difference in the definition of entropy when considering the classical thermodynamic picture vs. the quantum mechanical picture, or are they both fundamentally equivalent?
5
votes
3answers
620 views

Do quarks really exist?

Title says it all. Have they been seen in experiment or are they just theoretical things? Do quarks really exist?
2
votes
3answers
174 views

Can a wave possess spin?

Since a matter wave is associated with a particle in quantum mechanics, does the wave spins? I mean, can we visualize the spinning of wave or is it possible that the wave spins?
1
vote
1answer
135 views

Magnetic field of uniformly charged rotating hollow sphere

I want to compute the magnetic field due to a homogeneously charged, rotating sphere with radius $R$, angular velocity $\vec{\omega} = \omega\hat{z}$ and total charge $Q$. I want to use Biot-Savart ...
1
vote
2answers
59 views

Can electromagnetic fields be used to shield electromagnetic radiation?

Can electromagnetic fields be used as shielding for electromagnetic radiation?
0
votes
0answers
25 views

Using increase in pressure from melting of ice to produce energy? [on hold]

When ice is melted in a sealed piston, it would increase the pressure within and cause the piston to rise, right? Could this be combined with piezoelectric generator to produce electricity? If so, why ...
2
votes
6answers
2k views

How does velocity cause time dilation?

I've been trying to learn about the speed of light and time dilation, but I'm at an impasse. The presented facts say that if I travel around the solar system at 50% the speed of light and then come ...
0
votes
2answers
100 views

Can you confirm 2 simple statements about vaporization?

Vaporization is an interesting engineering subject, but unfortunately much about it has always been unclear to me. Recent research of mine has brought my mind to link vapor pressure to boiling and ...
0
votes
1answer
40 views

Effect of CO2 on the environment, besides greenhouse effect and ocean acidification [on hold]

What effects does the raising level of CO2 in the atmosphere have, besides being a greenhouse gas and responsible for the increased acidity of the oceans? What other environmental damages does it ...
0
votes
3answers
16 views

Vaporization in function of relative humidity

I am wondering how the relative humidity affects the vaporization? I saw on an other post that it doesn't affect it, but in my personal experience, it takes much more time to dry clothes when the ...
1
vote
1answer
835 views

The electric field of a conductive sphere containing a charge - grounded vs not grounded

Let's suppose we have a sphere but unlike theoretical ones it'll have some thickness say $\Delta r$ and inner radius $R$. What I was wondering about is how will it behave if we place some charge $q$ ...
2
votes
2answers
61 views

Mass of a black hole

I know that if a star collapses into a volume with radius less or equal to the Schwarzschild radius $r_s=\frac{2GM}{c^2}$ then a black hole is created and it has the same mass of the star that gave it ...
8
votes
3answers
232 views

Addition of spin angular momentum for massless particles

How do I add the spin angular momentum of massless particles, like photons, where only the transverse polarizations are allowed? If all three polarizations were allowed, this would be an easy ...
0
votes
0answers
37 views

“+” and “-” sign in Maxwell Stress tensor

I have trouble in determining the "+" and "-" sign of momentum per unit time, per unit area of the following question. Why in the second part, $d\vec{a}$ is pointing in the $ -\vec{z} $ direction? I ...
5
votes
1answer
180 views

Seiberg-Witten theory and Superconductivity

There seems to have some (deep) relation between Seiberg-Witten theory and superconductivity. e.g. this Witten paper. Q: Could someone introduce the relations between the twos both physically in ...
4
votes
2answers
241 views

QCD in the non-perturbative regime

In the list of unsolved problems in physics. Confinement: the equations of QCD remain unsolved at energy scales relevant for describing atomic nuclei. How does QCD give rise to the physics of nuclei ...
3
votes
1answer
201 views

Connected and strongly connected Feynman diagrams

Recently I read, that only connected Feynman diagrams give contribution of nonzero values into the scattering amplitude. Why it is so and what is the physical sense of connected diagrams (due to ...
1
vote
2answers
27 views

What would we observe from thompson's lamp thought experiment?

The thought experiment goes like this: Say there is some circuit which turns a lamp on/off with just a flick of a switch. Say its off; you flick it, it turns on; flick it again it turns off, ...
2
votes
1answer
71 views

Physics behind a match performing a trick on center of mass

https://www.youtube.com/watch?v=Ucdw0DDI4n8 I've seen another variation where the whole match stick turned to ash. What's going on in this trick?
0
votes
1answer
138 views

How can Superconductivity materials levitate permanent magnet?

I have thought that by eddy current. But how eddy current in superconductivity materials can be generated by using permanent magnet?
0
votes
0answers
45 views

Law of Gauss. Electrostatics

I have seen on the internet that many times people assert that inside a cylindric condenser the electrostatic field is null due to the fact that the Gauss flux inside is null. But I wanted to make ...
2
votes
2answers
53 views

Can 'Backradiation' warm its own source? [duplicate]

Ok, although this question arises out of the global warming debate, this is a question purely for physicists and not intended to branch into that particular debate. We are told that LWIR from the ...
17
votes
4answers
5k views

Birds sitting on electric wires: potential difference between their feet

We have seen birds sitting on uninsulated electric wires of high voltage transmission lines overhead without getting harmed, because sitting on only one wire doesn't complete any circuit. But what ...
4
votes
2answers
93 views

When did the first carbon atom in the Universe come into existence?

I am a chemist with a passion for astrophysics and particle physics, and one of the most marvellous things I have learned in my life is the process of stellar nucleosynthesis. It saddens me how my ...
2
votes
1answer
43 views

What is the energy of a black hole?

This might be a stupid question but given Einstein's general theory of relativity $E = m c^{2} $ what is the energy of a black hole? Isn't the mass of a black hole infinite? Wouldn't that be infinity ...
1
vote
1answer
61 views

Question concerning the Feynman Lectures of Physics

I am reading the Feynman lectures and at this point http://www.feynmanlectures.caltech.edu/I_13.html#Ch13-S3 it says as follows: The time derivate of the potential energy is $\begin{equation} ...
7
votes
3answers
168 views

Can we detect whether food has previously been heated in a microwave oven?

An acquaintance told me that she refuses to eat microwaved food because she read that the microwave changes the molecules of the food somehow. Her statement is vague and her sources are dubious but I ...
5
votes
2answers
221 views

What is the entropy of the universe today?

What's the entropy of the universe today? How does one go about calculating this? I've heard the statement that black holes account for the bulk of the entropy in the universe today, but don't know ...
0
votes
0answers
20 views

Visualizing Tension in FBD — Rope With Mass

Asked to find the tension of a point that is halfway up a rope (where the rope has mass), given the system: The solution of the problem (FBD included) is as follows. In this diagram (Tm = tension ...
0
votes
1answer
60 views

Why exactly are images formed by lenses/mirrors?

I just don't get the concept behind why a lens or a mirror forms a reproduction of the object at present. Is it to do with the object blocking parts of the light source? I just don't understand why an ...
3
votes
0answers
20 views

Why does the Fermi Surface cross the Brillouin zone boundary at right angles?

I'm not sure why the fermi surface crosses the Brillouin zone boundary at right angles. I understand that this is normally the case, but not necessarily always. I'm aware that the fermi surface is a ...

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