0
votes
0answers
3 views

Integrated Boltzman equation for dark matter

In Dodelson's book, the equation for a scattering process $ a + b \Leftrightarrow c + d $ is given as $a^{-3} \frac{ d (n_a a^3)}{d t}=-n^{\text{eq}}_a n^{\text{eq}}_b<\sigma v>(\frac{n_a ...
0
votes
0answers
7 views

Classical Mechanics, The Theoretical Minimum: error in answer to partial derivatives exercise?

I'm reading Leonard Susskind's Classical Mechanics, The Theoretical Minimum, and I'm on the interlude on partial derivatives. There is an exercise that asks you to find all of the first and second ...
0
votes
0answers
5 views

Apparent depth and real depth in terms of viewing angle

What is the apparent depth of an object in water in terms of : depth of object( $h$) refractive index of water ($\mu$) angle with which it is viewed from above ($\theta$) What I know : 1. ...
0
votes
0answers
8 views

Derivation of diffusion coefficient

For diffusion transport considering the "random walk" of electrons, I have the following derivation that leads to the diffusion coefficient $D$: $$d_1=d_2=\dots=d_n=\tau v \implies\\ \sum_n ...
0
votes
0answers
7 views

Why does the ball lose contact if it has velocity $>\qquad or \qquad< \sqrt{rg}$, while moving over a sphere of radius $r$?

Let a ball of mass $m$ is given a velocity over the the top of a smooth sphere of radius $r$. The equation of motion at the topmost point will be $$mg - N = m\dfrac{v^2}{r}$$ .As $v$ increases, $N$ ...
0
votes
0answers
7 views

Non trivial integral with the Bose-Einstein distribution and Cosine function

When I consider the Casimir interaction between an atom and a perfect conducting slab I find the following non trivial integral: $$\int\limits_0^\infty {\frac{{\cos \left( mx \right)}}{{x + ...
0
votes
1answer
11 views

If the velocity of an object, rotating on a vertical circle, at the topmost point is zero, how can it loop the whole circle?

Normally, if a body is attached to a string & is rotated in a vertical circle, then to loop the whole circle, the rope must not slack at the topmost point & there should be a velocity for ...
0
votes
0answers
7 views

Properties of the center of percussion

Can you please explain the article of wikipedia? If the blow falls above the CP (center of percussion) the movement of the CoG will cause the U-bolt to move away from the blow since the effect ...
-1
votes
1answer
31 views

How to derive Uncertainty Principle relation?

How to derive Heisenberg Uncertainty Principle relation? What experiments were conducted to prove the principle?
1
vote
0answers
17 views

Is there a name for the linear quantity corresponding to the (quadratic) “interval $\Delta s^2$”?

Recently it has been affirmed here (again) that the quantity called "interval (also 'spacetime interval' or 'invariant interval')" is referring to two (in general distinct) events as arguments, such ...
0
votes
0answers
7 views

When align the neutron's magnetic dipole moment, does moving neutron radiates?

Was performed an experiment in the past, where neutrons pass a magnetic field and their magnetic dipole moment get aligned? Was measured an electromagnetic radiation during the experiment?
0
votes
0answers
6 views

Are CMB photons entangled?

Suppose we'd like to know whether two CMB photons emitted from different parts of the sky have any quantum correlation with each other. We could measure polarization of two photons in different ...
0
votes
0answers
3 views

Do Two-wire Full Duplex Data Signal Cause Collison at atomic Level

Can the transmitting and receiving signal travel in the same wire in Full Duplex (FDD)? If yes, will there be any collision at atomic level? If yes, how this phenomena can be explained?
0
votes
0answers
18 views

When will Hamiltonian operator give a result that is not proportional to the function it acts on?

$$\hat{H}=-\frac{\hbar^2}{2m}\frac{\partial^2}{\partial x^2}+V(x),$$ $$-\frac{\hbar^2}{2m}\frac{\partial^2\Psi_n}{\partial x^2}+V(x)\Psi_n = E_n\Psi_n.$$ I was told that $\Psi$ is an eigenfunction ...
0
votes
0answers
4 views

Impact force on a Full Suspension Mountain Bike

I have a full suspension MTB design and i will do a structural analysis using a FEA tool.For this purpose,i have to calculate the forces applied on both wheels when the bike falls from a certain ...
2
votes
2answers
32 views

I there any tension in a massless spring that connects two free falling bodies in different horizontal planes?

Two bodies A and B of same mass $m$ are attached with a massless spring and are hanging from a ceiling with a massless rope. They are in same vertical plane but not in same horizontal plane. Now the ...
0
votes
0answers
13 views

How does one decide if the process if beta decay positive or beta decay negative?

I've been given a sample and a daughter product and I'll have to write down the other products of this decay process. This is a beta decay due to the mass number A being constant in the sample and the ...
1
vote
0answers
19 views

When one blows up a latex balloon, why does it get easier to blow once it has a little air in it (after 1 or 2 breaths)?

When one blows up a latex balloon, why does it get easier to blow once it has a little air in it (after 1 or 2 breaths)?
0
votes
0answers
7 views

Making a Bound State with Gamma Rays (and other Very High Energy Particles)

One obvious consequence of any finite potential is that a high enough energy wave-function will not form a bound state, either they are high enough energy they will generally just bypass the barrier ...
2
votes
2answers
85 views

Basic question about acceleration

Very basic question. Please show where I'm wrong in the following reasoning. The movement of an object in function of time could be described as $$ x(t) = v t + x_{i} $$ if velocity is constant. If ...
1
vote
0answers
6 views

What physical parameters are really being described when a rope manufacturer cites “elongation %”?

I have a precision pulley system sensitive to micron displacements. I am having issues because I need a cord with low tensioning force, but also low stretch. I am getting some weird hysteresis in the ...
0
votes
1answer
23 views

At what distance does a negatively charged atom not influence a moving free electron?

Don't know if it would be Gauss's law or Coulomb's law or both that would come into play here... but imagine a single negatively charged, stationary atom and a single free electron passing by it a ...
0
votes
0answers
17 views

Why does a panel of glass appear translucent when viewed from the edge?

Why does this happen? From the 'front' of the panel, the glass appears transparent. But viewed from the 'edges', it appears translucent...
-5
votes
0answers
24 views

what is the gravitational power of a supermassive black hole at the event horizon [on hold]

what is the gravitational power of a supermassive black hole at the event horizon i am currently theorizing time travel an would like to consider the possibility of charging a supermassive black hole ...
0
votes
0answers
22 views

Expectation value problems for non-eigenfunctions

This concerns problem 4 in this pdf file. The problems are fairly straight-forward if an assumption is made that $\psi(x)$ is an eigenfunction for the momentum operator. My question is: do we ...
1
vote
0answers
15 views

Other frequencies and breaking glass

I know an individual can use the natural frequency of glass to break it, but is it possible to break glass with a frequency other than the natural frequency? Will the glass still vibrate if the ...
0
votes
0answers
19 views

What are diamagnets and paramagnets?

A paragraph in my text reads: An atom or ion with all electrons paired is not attracted by strong magnets and is termed 'diamagnetic'. In contrast, spins do not cancel when unpaired electrons are ...
0
votes
0answers
16 views

Theory of chaotic systems : Bijective mapping

Considering a one-dimensional chaotic map $T$. The domain of the map (the closed interval $[0,\,1]=I_1 \cup I_1$) is partitioned into two regions (i.e. $I_0\cap I_1=\emptyset$): $[0,\,A] = I_0$ and ...
0
votes
0answers
8 views

What is the meaning of dielectric constant with AC fields?

I understand that in the DC case for parallel plates, a dielectric constant tells you by what factor the electric field gets reduced in the dielectric material vs. in vacuum. Does the same ...
0
votes
0answers
10 views

Wire loop in the magnetic field

I have strange problem, and no idea how to solve it. The wire loop $ ABCD $ is in a magnetic field of the long thin rod magnet with a magnetic moment per unit volume of $\mathfrak{M} _0 $ and a ...
1
vote
1answer
22 views

Torque required by motor to overcome magnetic force and gravity

I are trying to determine the torque and Power require from 2 nos motors to drive a wheeled robotic machine aka Crawler to overcome its own weight (Gravity) and force of the magnetic attraction. ...
-1
votes
0answers
10 views

how to build an anti proximity alarm [migrated]

I am trying to build an alarm that works in an opposite way to a security alarm in a shop. In shops RF tags on items set off an alarm as you walk through a detector. I wanted to build alarm that ...
0
votes
0answers
22 views

The image current due to moving charges and a current carrying thin wire

Suppose we have a plane conductor and positive charged particles of mass m are moving parallel to the plane conductor at a distance d. The trajectory can be assumed to be straight. An image current ...
-4
votes
1answer
39 views

Why Quantum Information was defined? [on hold]

Quantum Information Theory is a very much discussed term in Theoretical Physics, Information Science and Mathematics. Till now nearly 50 years after first definitions we have no usage in Computer ...
-3
votes
0answers
42 views

Is SHANNONs Information Theory useful today? [on hold]

SHANNON by himself excluded "psychological considerations". He was criticised very soon, because the word Information was used since time of Romans (informatio).
0
votes
2answers
69 views

Explain why quantum behavior is not observed in daily life

People always ask: How come we don't see any "Wave" attached to a classical object such as a car? You always see the object in the same place without any uncertainty. I am sure there are answers, ...
0
votes
1answer
27 views

Photoelectric effect and light coming in chunks

I was watching a lecture on introduction to quantum mechanics.While explaining the photoelectric effect,the lecturer mentioned that we must think of light as coming in chunks with each chunk having ...
0
votes
0answers
9 views

Difference between thin film interference and Bragg diffraction of electron

Thin film interference is given by: $2dsin\theta=n\frac{\lambda}{n_i}$, where $d$ is the thickness of film, $\theta$ is the angle between incident light and tangent to the surface, $n$ is an integer, ...
0
votes
1answer
66 views

Post mortem measurement of particle-wave duality

I was wondering what the outcome of this experiment would be: You shoot single photons at a double slit. On their way there you preform a measurement in $x$ so you get the time ($t_0$) the particle ...
0
votes
0answers
20 views

Hawking Radiation and Curvature

From a simple point of view in GR/QM we take a virtual pair creation and presumable they reunite shortly in flat space-time probably representable by a space-time warpage that generates geodesic ...
0
votes
1answer
46 views

Basic concepts on Electricity [on hold]

How do electrons move? I mean really do they move? I read that they move in circular shells AROUND THE NUCLEUS. How can they move in the conductor? I have read that there are valent electrons that ...
0
votes
0answers
17 views

Mach-Zehnder interferometry wave functions

Consider the set up below: I have read that in the apparatus the wavefunction is given by: $$|\psi \rangle=e^{i\theta}|c \rangle +i |b \rangle$$ where $\theta$ is the phase added by the phase ...
0
votes
2answers
65 views

What force needs to be applied to produce twice as much acceleration as already present in a body?

Let the current body of mass $m$ be moving with acceleration $a$, produced by applying $F = ma$. So, I thought that if I apply force $F$ again (same magnitude and direction as before), I would get ...
1
vote
0answers
35 views

Is there any other momentum besides the Poynting momentum stored in an electromagnetic field?

I am having some conceptual difficulties with energy and momentum stored in the EM field. The force density at a point is $\rho E + j\times B$ Because of conservation of momentum, and because the ...
0
votes
1answer
11 views

Incoherent Intermediate Scattering Function from Molecular Dynamics Simulations

I want to calculate the incoherent intermediate scattering function (ISF) using the self-part of the van Hove function. When I plot the ISF as a function of time, should I consider the modulus of the ...
-1
votes
1answer
17 views

Electrostatics Problem - A non-conducting cylinder [on hold]

A nonconducting cylinder of radius 1.20 meters and length 2.00 meters carries a charge of 50 micro-coulombs uniformly distributed throughout the cylinder.Find the electric field on the cylinder axis ...
0
votes
0answers
33 views

How to go from Lorentz gauge to Coulomb gauge?

I want to know that if I find some solution, say a polarization vector in Lorenz gauge. Now I want to go to Coulomb gauge. There must be a transformation that links both the gauges. How would I find ...
0
votes
1answer
18 views

Motion in oscillating field: expanding in powers of $\xi$

I'm reading an excerpt from Landau/Lifschitz's Mechanics book about motion in oscillating fields. Two equations for the motion of a particle with mass $m$ are set out: \begin{equation} m\ddot{x} = ...
0
votes
1answer
40 views

What is the significance of Planck charge?

It seems for me that Planck units are somehow connected to limits where our current knowledge breaks down because of (quantum) gravitational effects. Please correct me if I'm wrong. For example ...
0
votes
1answer
36 views

Why does the temperature of a gas inside a moving container not increase with velocity?

A rectangular (simplified) container with rigid surfaces, has a certain mass of ideal gas within it, and it accelerates in free space, undergoing rectilinear motion. There are no dissipative ...

15 30 50 per page