# All Questions

4k views

### Unified field theory in layman's terms

I watched some videos on the unified field theory, specifically interviews with Michio Kaku and John Hagelin, and want to learn a bit more about it. I looked up the theory of everything, string theory ...
972 views

### What is the proof that a force applied on a rigid body will cause it to rotate around its center of mass?

Say I have a rigid body in space. I've read that if I during some short time interval apply a force on the body at some point which is not in line with the center of mass, it would start rotating ...
151 views

### Are group representations possible when the solution space is not a vector space?

As far as I understand, the motivation for using representation theory in high energy physics is as follows. Assume that a theory has some (internal or external) symmetry group which acts on a vector ...
6k views

### Dirichlet and Neumann Boundary condition: physical example

Can anybody tell me some practical/physical example where we use Dirichlet and Neumann Boundary condition. Is it possible to use both conditions together at the same region? If we have a cylindrical ...
268 views

### How frequency generated on water can affect it's flow on camera?

I have a science fair project, and it can be summed up in this video. The problem is that only a sub woofer can generate a pure 23.24 Hz frequency and I can't afford a sub woofer. So I was wondering, ...
154 views

### 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 ...
391 views

### 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. ...
379 views

### 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 ...
99 views

### 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 ...
997 views

### 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 ...
394 views

### 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 ...
174 views

### 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 ...
102 views

### 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 ...
192 views

### 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 ...
202 views

### 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 ...
2k views

### 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, ...
119 views

### 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 ...
153 views

### 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 ...
194 views

### 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 ...
108 views

### 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 ...
184 views

### 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 ...
119 views

### 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 ...
150 views

### 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 ...
335 views

### 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 = ...
645 views

### 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 ...
173 views

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 ...
122 views

### 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 ...
233 views

### 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 ...
149 views

### 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 ...
1k views

### 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, ...
1k views

### 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 ...
126 views

### 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 ...
185 views

### 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. ...
114 views

### 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; ...