0
votes
2answers
96 views

Gaussian surfaces and Gauss law

Does Gauss law holds for any closed surface or it only holds for only Gaussian surface. Are every closed surface a Gaussian surface?
2
votes
1answer
52 views

Measure the phase of a quantum field?

Is it possible to measure the phase of a quantum field or quantum particle, as an observable?
0
votes
1answer
156 views

Physical meaning of the creation or annihilation operators for a N-electron gases?

For a N-electron gases in a finite volume V, what is the meaning of the first "=" in the following expression: ...
-8
votes
1answer
183 views

Are there any causeless phenomena from the mainstream physical viewpoint? [closed]

EDIT: The orginal version did not produce any answers about physics. I know what life is, I have studied that for decades. I wanted to hear how the border between matter and spirit looks from the ...
1
vote
1answer
218 views

What are some good resources for learning how to apply vectors in physics?

Although I don't have any problems with vectors when using them in Mathematics but I am having a hard time using them in physics. It is really frustrating me. Can you please recommend me some good ...
1
vote
1answer
72 views

Finding at a distance from the Earth speed of satellite [closed]

A satellite at 8000 km from Earth where gravity is 6.4 m/s^2. What is the velocity of satellite? I don't the formula to find speed of satellite.
-3
votes
1answer
66 views

Finding resistance [closed]

Two resistors when connected in parallel give the resultant value of $2\,\Omega$, when connected in series the value becomes $9\,\Omega$. Calculate the value of each resistance.
0
votes
2answers
217 views

The entropy of the universe in an irreversible cycle [closed]

Suppose we have an ideal gas performing an irreversible cycle composed by: an isothermal transformation at $T_{1}$; an isobaric transformation at $P_{A}$; an isothermal transformation at $T_{2}$; an ...
2
votes
4answers
197 views

Can nuclear transmutation be observed in real time?

Ignoring the quantum zeno effect (if possible?), can we observe in real-time the transformation of one element to another? I'm talking about an amount visible to the naked eye where one could see ...
0
votes
1answer
47 views

Is it possible to create a solar cell in home? [closed]

I'm not really sure that this is the place to ask this question, but anyway. I'm curious is it possible to create a solar cell (not panel with 2$ cells from ebay) in home. If not why and if yes how. ...
18
votes
1answer
1k views

Photobombing without app used by Harley Davidson

Here we see a photobombing trick, used by Harley Davidson. They achieve to incrust a logo on a photo you take. The logo is invisible with naked eyes and only revealed on the photo you take. How does ...
1
vote
3answers
211 views

Apparent dimensional mismatch after taking derivative

Suppose I have a variable $x$ and a constant $a$, each having the dimension of length. That is $[x]=[a]=[L]$ where square brackets denote the dimension of the physical quantity contained within them. ...
1
vote
1answer
52 views

Velocity in frame $S$ and $S'$

If I take the Lorentz position transforms between two inertial frames, $S$ and $S'$ moving with relative velocity $u$ along a common axis (say $x-x'$), then: $$x'=\gamma(x- ut)$$ $$y'=y$$ $$z'=z$$ ...
2
votes
1answer
146 views

Current, Current density

edit: Hi I'm trying to find the magnetic field generated by a time dependent oscillating current in the quasistatic case ($|z|,r <<c\omega$) where r is the perpendicular distance from the ...
2
votes
3answers
3k views

Can an electromagnet repel a strong magnet?

When the direction of current is reversed, the polarity of an electromagnet should be reversed. I am trying to understand why this did not happen in an experiment I conducted today. An electromagnet ...
1
vote
2answers
827 views

time dependent current/ magnetic field

Is there a general way to calculate the magnetic field for a time dependent current of a long thing wire? For ex: If the current is $$ I(t)=I\sin wt, $$ is there a general method to use in order to ...
1
vote
1answer
201 views

Superluminal travel without time travel

Can superluminal travel or communication be possible without leading to the possibility of closed timelike curves (CTCs) and causality violations? I have seen conflicting opinions regarding this ...
2
votes
1answer
68 views

Locality in Condensed Matter Lattice Model

What is a proper definition of locality in condensed matter lattice model? I emphasize "condensed matter" because there is no Lorentz symmetry or "speed of light". I think it is quite important ...
8
votes
3answers
915 views

Does electron-electron scattering contribute to resistivity?

Electron-phonon and electron-defect scattering clearly contributes to resistance, but pure electron-electron scattering conserves the total momentum (and energy) of all the electrons. Then, how is it ...
0
votes
1answer
102 views

Is there any way to find difference between two same sounds of different people?

I am trying to understand and find a way to distinguish two same sounds of different people by some physics formula, so could you guys help me? OK I'll try to explain my question in this way that, ...
15
votes
4answers
2k views

Force as change in momentum vs. change in velocity

Is there ever a situation where the distinction between $F = m \frac{dv}{dt}$ and $F = \frac{dp}{dt}$ is important? I can't think of a situation where one is true and not the other (assuming only ...
2
votes
0answers
490 views

Why is free neutron unstable but free proton is stable?

Aren't they basically made up of the same stuffs (quarks) in almost the same configuration?
0
votes
2answers
55 views

Importance of the study of the diatomic molecule [closed]

I wanted to know the importance and applications of the study of the diatomic molecule in physics I know that the question may not make much sense to you, but while exposing the solution of relative ...
3
votes
4answers
359 views

Isn't $E-U = K$ in Schrodinger's Equation?

I'm studying quantum mechanics in its most basic level (I don't even know if Physicists call this already quantum mechanics) and I have one doubt in Schrodinger's equation. The book presents the ...
0
votes
1answer
175 views

Jackson equation 2.9; How to derive it?

I wanted to understand the derivation of Jackson's equation (2.9) that you can find here on page 31 (50/661) from the potential given earlier. This equation is written as: $$ ...
0
votes
2answers
67 views

Mass,Energy,Matter

In $E=mc^2$ what type of energy is $E$? For instance, you can find the kinetic energy of an electron by using $\frac{1}{2}mv^2$ but you can also find the energy from $E=mc^2$. How are those two ...
0
votes
1answer
41 views

Applying conservation of energy to any system?

How would the conservation of energy be applied in any system? Can we always be certain that every system will always obey COE? How can we be certain without measuring the system? Input & Output? ...
6
votes
5answers
506 views

Infinities in Newtons law of gravity (for point particles)

Newtons law of gravity for two particles of mass $m_1$ and $m_2$ is: $G\frac{m_1.m_2}{r^2}$. Supposing that the particles are point particles then gravitional attraction will bring them closer ...
2
votes
0answers
269 views

The anapole moment, derivation from Dirac current density

Basically I am looking for a way to expand the electromagnetic interaction energy $W = A_{\mu}j^{\mu}$ (both $A$ and $j$ obtained from the Dirac equation) similar to the classical expansion in ...
0
votes
1answer
100 views

Steady state average of physical quantities

Consider the following Hamiltonian: $$ H = \sum_n \left[\dfrac{p_n^2}{2m_n} + U(x_l) + V(x_{l+1} - x_l) \right], $$ that corresponds to a 1-D system of particles with nearest-neighbor interactions ...
1
vote
0answers
241 views

Is it possible to increase the electromagnetic repulsion between two particles?

Given the fact that the force stopping me falling through the ground is the electromagnetic repulsion between the electrons in my feet and the ground, would it be possible to increase this repulsive ...
6
votes
3answers
641 views

Why does Minkowski space provide an accurate description of flat spacetime?

What is the chain of reasoning (beginning, of course, from observations about the universe) that leads one to predict that Minkowski space provides an accurate description of space-time in the ...
2
votes
0answers
61 views

Confused about time dilation/length contraction [duplicate]

I have a following problem: A meson is generated $h$ meters above the earth's surface and begins to move towards the earth with velocity $v$. Its (proper) lifetime is $t_m$. What is $v$ if the meson ...
1
vote
2answers
155 views

The relationship between the Hubble Constant and cosmological time [duplicate]

I am a first year student at varsity and I am new to Astronomy. A question came up in my tut asking about the Hubble constant and cosmological time. I couldn't answer it because I have not understood ...
6
votes
4answers
2k views

Do particle velocities in liquid follow the Maxwell-Boltzmann velocity distribution?

The Maxwell-Boltzmann velocity distribution arises from non-reactive elastic collisions of particles and is usually discussed in the context of the kinetic theory (for gases). There are various ...
2
votes
1answer
136 views

Can a single photon induce current in a very small coil?

As I know from Lenz's law, I can induce current in a coil just by changing the magnetic field flux inside the coil. As I know from physics course, photons are electromagnetic waves (so they are the ...
4
votes
2answers
229 views

What guarantees the existence of unitary operators implementing Lorentz Transformations?

This should be a very basic question. In introductory QFT books, often one of the first things we see is the following claim: for every Lorentz transformation $\Lambda$, we can associate an unitary ...
0
votes
1answer
303 views

changes in horizontal velocity and the effect on time airborne (thus overcoming gravity)

I would like to know if a object is launched horizontally in the air at a lower speed and a higher speed, why does the higher speed keep it airborne longer. what are the forces and why does gravity ...
3
votes
1answer
113 views

Put yourself in the shoes of Wolfgang Pauli (1930): How could Pauli have narrowed the culprit down to one particle, instead of many?

A while ago, during my introductory physics course, my professor purposefully neglected to tell us about the existence of the anti-electron neutrino in beta decay; he made it an assignment(on our ...
0
votes
3answers
98 views

Photon Quantum Field proportional to Electromagnetic Field?

Does it make sense to say that the quantum field of a photon is exactly proportional to the photon's electromagnetic field? \begin{align} \bar{\Psi} = \dfrac{\bar{E}+i\bar{B}}{\sqrt{\int ...
1
vote
0answers
59 views

Non-trivial components of the stress-energy tensor of the bosonic string ghost action

The stress-energy tensor derived from the ghost action of a bosonic string is: $$ T_{\alpha \beta} = \frac{i}{4 \pi} \left ( b_{\alpha \gamma} \nabla_{\beta} c^{\gamma} + b_{\beta \gamma} ...
0
votes
2answers
247 views

Olympic weight lifting bar, plate location affect

I apologize in advance for the rudimentary nature of my question. A perfectly balanced weight lifting bar is loaded with three weight plates on each side. The three plates are 25kg, 10kg and 5kg. ...
2
votes
1answer
85 views

Proof that 4-potential exists from Gauss-Faraday field equation

This is a problem concerning covariant formulation of electromagnetism. Given $$\partial_{[\alpha} F_{\beta\gamma]}~=~ 0 $$ how does one prove that $F$ can be obtained from a 4-potential $A$ such ...
1
vote
0answers
258 views

Fluctuation-Dissipation theorems in an infinite quantum system

So for a quantum spin chain, one can easily prove via the partition function that you have a fluctuation-dissipation type relation between the magnetic susceptibility and the variance of the ...
1
vote
2answers
1k views

First Order Phase Transition - Heat Capacity

At constant pressure : $\frac{dH}{dT}=C_p $ Hence, why doesn't the graph of $C_p$ against $T$ show two perfectly horizontal lines (with the obvious discontinuity) ? I mean the gradient of $H$ ...
2
votes
2answers
74 views

Derivation of a quantum dynamical map on open quantum system

Let us consider a initial total quantum system as $\rho(0) = \rho_S(0)\otimes\rho_B$ where $\rho_S(0)$ is initial open system and $\rho_B$ is density matrix for environment. We can use partial trace ...
3
votes
4answers
5k views

Why does sound need air in order to travel?

I know that in space, because of vacuum that we can't hear voices or sound to be specific, why is that? Why does sound need a medium to go through?
4
votes
2answers
735 views

What does it mean to “convert energy into time”?

In a recent article about creating electron-positron pairs by colliding photons in a laboratory, Andrei Seryi, director of the John Adams Institute at Oxford University, was quoted to said: It's ...
0
votes
1answer
783 views

Measuring flow rate of gases

Flow rates of liquids could be easily measured with a stopwatch and a known volume container. But gases, if entrapped in a container will create a back pressure, and may lead to decreased flow. I ...
1
vote
0answers
67 views

Long range order in the BCS ground state

I am trying to prove the following equivalent form for long-range-order in superconductivity (Annett's book states something like this) : \begin{equation}\lim_{|R-R'|\to ...

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