# All Questions

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### The physical laws of thermodynamics tell us that electrical impulses must produce heat?

Health - Controversial New Idea: Nerves Transmit Sound, Not Electricity - By Robert Roy Britt, LiveScience Managing Editor posted: 14 March, 2007 1:00 pm ET Rendering shows a biological membrane ...
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### Has The Aharonov-Bohm Effect Been Experimentally Proven?

I have encountered two contradicting papers on the Aharonov-Bohm Effect: One supporting, The Aharonov-Bohm Effects: Variations on a Subtle Theme. H Batelaan and A Tonomura. Physics Today 62 pp. ...
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### Solving the 1-D Schrodinger equation for a free particle: Confused about 2 possible general solutions

I am following Griffiths' Introduction to Quantum Mechanics, as well as an online lecture that follows a different book, and both sources give different equations for the general solution of the 1-D ...
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### Given a state function of a particle, can we determine its mass?

The quantum state of a system is supposed to contain all the information that can be obtained about the system such as its energy, momentum...etc. So I have 2 questions: 1-If someone gave us a ...
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### Calculating lifetime of a pi meson via Heisenberg uncertainty relationship?

This is a problem from my textbook: "A proton or neutron sometimes 'violates' conservation of energy by emitting and then reabsorbing a pi meson, which has a mass 135MeV/$c^2$. This is possible as ...
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### Impulse from absorbing a photon? Is there an increase in rest mass?

I'm going through A P French's special relativity. In one chapter (6) the following is set up: Suppose that a stationary particle of mass $M_0$ is struck by a photon of energy $Q$, which is ...
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### Quantum Ripples?

Would someone please explain what quantum ripples are? I've heard of gravitational waves, are they the same thing? I overheard someone saying that it could allow for possible faster than light speed ...
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### Quantum yield and spontaneous decay

I'm trying to figure out how many atoms are decaying spontaneously in a span of 2 seconds. Let's say that the quantum yield is 0.45, and that the lifetime "τ" (tau) is 10 microseconds. Then I found ...
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### Does a constant factor matter in the definition of the Noether current?

This is a very basic Lagrangian Field Theory question, it is about a definition convention. It takes much more time to typeset it than answering, but here it is: Consider a field Lagrangian with only ...
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### How do particles, such as electrons become visible?

Quantum mechanics says that atoms are invisible - they do not have some specified location, only a probability distribution. So, how can we see them? If there is to be particle-antiparticle ...
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### DC Motor Torque Constant

I am very new to DC motors and to stackexchange. Please correct me if anything I said does not make sense. For DC motors, the equation looks like this: $P = \tau\dot{\theta}$ where $P$ is power, ...
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### Charged plane in an electric field acceleration

A perpendicular plane to an electric field's lines of force has more electric flux than a plane that is in parallel with the lines of force, right? Does this mean that a charged plate would ...
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### Escape Velocity question

I would like some help in understanding the derivation of the formula for escape velocity. Why does $t$ approach infinity? And why is $v(t)$ approaching zero? I know that $r(t)$ is infinite because ...
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### Transform torque from Euler angles to infinitesimal Cartesian rotations

For a certain pair of rigid bodies, I have the gradient of energy in terms of Euler angles. I want to transform this gradient to the gradient of energy in terms of rotations about the $x, y, z$ axes ...
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### Data For Quantum Entanglement

Is there any publicly accessible data that shows quantum entanglement empirically. I want to see what these researches are seeing that is showing them that indeed this phenomenon is real. Also, any ...
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### Electron in a uniform magnetic field and center of the circumference

I have an electron in a 3D space and there is a uniform constant magnetic field $B$, oriented according to z-axes. At $t=0$, we have $z=0$ and $\dot z =0$. I have proved that the trajectory is a ...
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### Clarification on factors of $c$ in the Lorentz' force

I was told that Lorentz' force is given by $${\bf F}= q{\bf v} \times {\bf B}.$$ But I have read that it is given by $${\bf F}= \frac{q}{c}{\bf v} \times {\bf B}.$$ Why have these two relations ...
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### Is there an upper limit to wavelength and particle size in the Mie Scattering solution?

I figure that Mie scattering is best for finding the scattering when the wavelengths are between 1/10th to 10x the particle diameter. However, is there an upper limit to this? If I send 2.8cm ...
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### Irradiance (or intensity) of an electromagnetic wave

Is the irradiance (or intensity) of an electromagnetic wave given by $$I = \left<\|\mathbf{S}\|\right>_{T}$$ or by I = ...
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### Amplitude of Probability amplitude. Which one is it?

QM begins with a Born's rule which states that probability $P$ is equal to a modulus square of probability amplitude $\psi$: $$P = \left|\psi\right|^2.$$ If I write down a wave function like this ...
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I am currently reading about electric flux; and from this passage I am reading, I am sensing a bit of a contradiction: "If the E-field is not perpendicular to the surface area, then the flux will be ...
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### Circular Polarization

As one observes an clockwise (cw) circular polarized electromagnetic wave which is reflected off a denser medium or metal interface it is changed to a counter-clockwise (CCW) polarized em wave plus a ...
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### Probability and probability amplitude [duplicate]

What made scientists believe that we should calculate probability $P$ as the $P = \left|\psi\right|^2$ in quantum mechanics? Was it the double slit experiment? How? Is there anywhere in the ...
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### In Noether's theorem, what is a “classical solution of the equations of motion”?

I'm reading a book which states that: for each generator of a global symmetry transformation, there is a current $j^{\mu}_{a}$ which, when evaluated on a classical solution of the equations of ...
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### Statistical Mechanic

One can define entropy as $$S=k\log{\omega(E)},$$ where $\omega(E)$ is the numbers of states with energy equal $E$; and the canonical partition function for a set of N particles is defined ...
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### Solving the time independent Schrodinger equation: Does a complex solution make sense?

In my notes, I have the Time Independent Schrodinger equation for a free particle $$\frac{\partial^2 \psi}{\partial x^2}+\frac{p^2}{\hbar^2}\psi=0\tag1$$ The solution to this is given, in my notes, ...
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### Calculating displacement amplitude of ultrasonic power transducer

I am not a physicist, but my current project drives me to some physics-related computations, hence seeking help. I have some ultrasonic transducers, 5938D-25LBPZT, for which very limited information ...
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### Carrier Electrons Generation and Recombination Time

When a Electron gets promoted to the conduction band from valence band (In generation) lets say for example in Silicon at room temperature. Is there any way to determine (on average) how long it will ...
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### Reference on Chern-Simons theory [duplicate]

I have recently been trying to refresh my memory on the Quantum Field Theory I learned 25 years ago while getting my Ph. D. At the time I did not study Chern-Simons modifications to QFT Lagrangians. ...
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### Weightlessness on Earth

Would the following work? Imagine one would 1) create a straight 4000 km long tube (at ground level), following the curvature of the Earth, wide enough to hold a pod the size of an aircraft cabin; ...
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Assume my time value is \$0. High gas heat adds more energy per second to the water but the pot may absorb the heat less efficiently, or maybe the shape of the flame is less good, or for other reasons ... 1answer 125 views ### Can we project a 4D world using 3D video technology? Traditional movies, TV, etc, faithfully show our 3-dimensional world using 2 dimensions. So can we have a movie that shows a 4-dimensional world using 3D technology? 1answer 308 views ### Does weather obstruct microwaves and radiowaves? I read an article ('How airplanes use radar' at Bright Hub.com) that stated that airplanes use radio waves for communication because they aren't obstructed by weather. Is this true? 5answers 313 views ### Confusion regarding photons? I'm still in high school, and while I can't complain about the quality of my teachers (all of them have done at least a bachelor, some a masters) I usually am cautious to believe what they say ... 3answers 416 views ### Why do clocks measure arc-length? Apologies in advance for the long question. My understanding is that in GR, massive observers move along timelike curves$x^\mu(\lambda)$, and if an observer moves from point$x^\mu(\lambda_a)$to ... 3answers 258 views ### Relativistic equivalent of a spring-force? Usually what helps me understand a concept better in physics is to write a simulation of it. I've got to the point where I'm competent in the basics of special relativity, but, I can't figure out how ... 1answer 238 views ### Is There a List of Physics Formulas? [closed] I am looking for a list of simple physics formulas - like$F=ma$. Is there any website/book that is a list of such equations? 1answer 159 views ### Photons, no energy? [duplicate] I am only 14, so I don't know much about physics, and I would appreciate help on this topic. A photon, is said to have 0 mass. However, they carry energy, as electromagnetic radiation. Albert ... 1answer 124 views ### Real World measurements related to phonon dispersion I hope no one objects to the style of this question. Let me explain my motives in asking the question first. Condensed matter physics is one of the most beautiful subjects around. But those who are ... 1answer 507 views ### Dimension of Dirac$\gamma$matrices While studying the Dirac equation, I came across this enigmatic passage on p. 551 in From Classical to Quantum Mechanics by G. Esposito, G. Marmo, G. Sudarshan regarding the$\gamma$matrices: ... 0answers 89 views ### Is a solution to the Klein-Gordon equation homeomorphic (or even diffeomorphic) to a solution of an equation with a different covariance group? Consider some solution$\psi(x,t)$to the linear Klein-Gordon equation:$-\partial^2_t \psi + \nabla^2 \psi = m^2 \psi$. Up to homeomorphism, can$\psi$serve as a solution to some other equation ... 1answer 74 views ### How accurate are our calculations about distant stars keeping in mind their enormous distances? Since many stars are hundreds of light years away from the earth and therefore, what we observe of them today is really their distant past, how can we say anything with certainty about their ... 1answer 130 views ### How scientists could say that such meteorite comes from Mars How could scientists affirm that a meteorite comes from Mars and not from another source ? This is a probability or an absolute certainty ? How much percent ? 2answers 141 views ### How to comoving volumes depend on the evolution of the Universe? I'm reading a paper which states that Neutron star binary merger rate at redshift$z$per unit observer time interval per unit volume is$\dot{n}_{m} = \dot{n}_{0} (1+z)^{2} (1+z)^{\beta}$, ... 2answers 519 views ### What exactly is the difference between a sychrotron light source and a free electron laser? Cyclotron radiation is radiation emitted by a charged particle being bent by a magnetic field. The only difference between cyclotron and synchrotron radiation is that the latter occurs at relativistic ... 0answers 51 views ### Orientation in GaAs I can't find the precise definition of what is the orientation of a GaAs lattice. Being the superposition of two fcc lattices (one of Ga, the other of As), I would think that it is the direction of ... 1answer 165 views ### Chiral perturbation theory: what is the Quark Condensate? why expand in$U\$ rather than Goldstone fields?

I'm studying Chiral Perturbation Theory (ChPT) from Scherer's manuscript "Introduction to Chiral Perturbation Theory", available at http://arxiv.org/abs/hep-ph/0210398 What I am currently having ...
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### Relationship between frequency and wavelength [closed]

I am currently writing up a report for science class on the relationship between frequency and wavelength. And so I was wondering if anyone knew where I could find published results (literature value) ...