All Questions

Filter by
Sorted by
Tagged with
0
votes
0answers
4 views

How to understand produce optical standing wave by mirror reflecting with half-wave loss

Considering the incident optical wave $E_i=e^{ikx}$ and reflect optical wave $E_r=e^{-ikx+\pi}$,where $\pi$ corresponding the half wave loss.The superposition of incident wave and reflect wave is $E=...
0
votes
0answers
12 views

Entropy change in sudden expansion

For an irreversible sudden expansion from $V$ to $2V$, no heat is added during the expansion. However, the entropy changes by $N\log2$. I'm not sure how there can be a change in entropy without any ...
1
vote
0answers
8 views

what is angle of escape velocity [duplicate]

We know if a object has escape velocity(EV) it reaches space(ignore atmosphere friction), but at what angle. if an object travels parallel to earth surface with EV, will it escape curvature and reach ...
0
votes
0answers
4 views

Understanding time-domain tecnique for the calculation of black hole quasi normal modes

I am working on black hole quasi normal mode, in particular I am working on the time domain tecnique for the calculation of QNM. I am studying this paper by Carsten Gundlach, Richard Price, Jorge ...
-1
votes
0answers
9 views

Book review - SS Krotov

How good is the book, Physics for everyone by SS Krotov? What is the difficulty level and it's relevance to the Physics Olympiad.
0
votes
0answers
4 views

Intuiting qualitatively the shapes of the eigenfunctions of a finite well-like potential, using the infinite well eigenfunctions as an inspiration

Consider, for example, the third excited state of an infinite square well: Now consider the following potential: If we wanted to sketch the rough shape of the third excited eigenfunction of this ...
1
vote
1answer
15 views

Combining gravity with other forces

We all know we have 4 fundamental forces, and among them we can combine 3 forces but not gravity as in Standard model and some other. But force is something we can measure, as Einstein told us in ...
1
vote
0answers
14 views

Verlinde formula requires compact Riemann surface

Assume a Chern-Simons theory on a 3-mfld of the form $\Sigma_g \times S^1$, where $\Sigma_g$ is a Riemann surface of genus $g$. In his paper, Witten shows that one can use the Verlinde formula to get ...
1
vote
2answers
45 views

Tensor and Matrices

Suppose that we are dealing with the following matrix: $$A=\begin{bmatrix}a_{00} & a_{01} \\ a_{10} & a_{11}\end{bmatrix}$$ but I don't want to use matrix notation, insted I want to use tensor ...
1
vote
2answers
32 views

Query regarding $L^{2}$ functions

Given that a wave-function $\psi$ can be written as the superposition of plane waves where $\mathbf k$ is the wave vector (3D) and $g({\mathbf k})$ is a complex fn. Now, the author states that, any ...
0
votes
0answers
10 views

Metric Tensor in Weak Field Condition [duplicate]

Suppose that we are in the Weak Field Condition, that is: $$g_{\mu\nu}=\eta _{\mu\nu}+h_{\mu\nu}$$ where $\eta _{\mu\nu}$ is the metric tensor of flat space time (Minkowski spacetime) and $h_{\mu\nu}$ ...
0
votes
0answers
8 views

Boltzmann equation and phase space measure in curved spacetime

Here I have attached Boltzmann equation from wikipedia. https://en.m.wikipedia.org/wiki/Boltzmann_equation#:~:text=The%20Boltzmann%20equation%20or%20Boltzmann,by%20Ludwig%20Boltzmann%20in%201872. ...
-1
votes
0answers
20 views

Why is the extended length of the spring 0.268? [closed]

I am unable to grasp why the spring stretches by 0.268 ft. I know that 2 - 1.732 is where 0.268 comes and 1.732 is the projection of length AD. So why is the spring trying to ensure that the length ...
0
votes
0answers
17 views

What are future hypothetical technical applications of modern physics? [closed]

Maxwells theory of electromagnetism led to huge advances in communication technology. Quantum mechanics combined with statistical physics helped us to understand solid state physics and this ...
1
vote
1answer
26 views

Does the object move when the forces are balanced but is rotating?

If we apply $F=ma$, there is no net force and as such there is no acceleration in the center of mass. But due to the friction acting, there is a torque which gives rise to an angular acceleration of ...
0
votes
0answers
12 views

Why is refraction of light at a boundary wavelength dependent, and are the two proportional?

Just wondering, why is it that blue light will refract less than red light, i.e. why does the fact that blue light has a shorter wavelength mean that it will refract less at a boundary? I read ...
2
votes
1answer
38 views

Why isn't the second defined by fixing $G$?

Since 2019, the meter, kilogram, ampere, and kelvin, are defined by setting exact numerical values for the speed of light $c$, the Planck constant $h$, the elementary charge $e$, and the Boltzmann ...
0
votes
0answers
17 views

surface charge density $\hat{\rho}$ and surface current density $\hat{\mathbf{j}}$

I am currently studying the textbook Principles of Optics: Electromagnetic Theory of Propagation, Interference and Diffraction of Light, 7th edition, by Max Born and Emil Wolf. Page 5, chapter 1.1.3 ...
0
votes
1answer
18 views

Different drift velocities in the same conductor

We know unlike charges attract and like charges repel. The magnitude of this force of attraction or repulsion decreases as the distance between the charges increase. As a result the force exerted due ...
0
votes
1answer
52 views

What does the notation $|\text{grad} \ F|$ mean?

I am currently studying the textbook Principles of Optics: Electromagnetic Theory of Propagation, Interference and Diffraction of Light, 7th edition, by Max Born and Emil Wolf. Page 5, chapter 1.1.3 ...
-1
votes
0answers
18 views

Question regarding polar coordinates [closed]

A point particle travels along the curve y = x2. At t = 0, the particle is at the origin. Assume that the angular velocity is positive. a) Determine r as a function of . b) Can the angular ...
0
votes
0answers
17 views

Are there any reasons that speak against defining an “extended” voltage to be the line Integral of the complete Lorentz force?

While writing down the equations for circuit theory in the presence of changing magnetic fields \begin{align} U_{ab}=\int_a^b \vec{E} d\vec{s} \\ \sum_i U_i = - \int_{loop} \dot{\vec{B}} d\vec{a} \...
0
votes
1answer
7 views

Definition of eclipsing binaries?

In the second minimum (the 3rd step) there is a smaller decrease in light intensity. For this to happen, wouldn't you need to be looking at the plane of orbit from above rather than directly along the ...
1
vote
2answers
25 views

Intuitive Explanation for Doppler effect?

I was looking for an intuitive explanation as to why the Doppler effect happens. I haven't found any, but this is what I thought: -Waves emitted travel at a constant speed -The source emits a wave -If ...
0
votes
0answers
17 views

Normal modes of vibration from the total energy

A mass $m$ is restricted to move in the parabola $y=ax^2$, with $a>0$. Another mass $M$ is hanging from this first mass using a spring with constant $k$ and natural length $l_0$. The spring is ...
2
votes
0answers
50 views

What's the meaning of 'understanding' in physics?

I read this article which is on how Feynman thought of the difference between physics and mathematics. Feynman's point is that physics is to understand nature while mathematics is to make their own ...
0
votes
0answers
14 views

What quantity should be used in the Stefan-Boltzmann Law?

I am currently looking into the Stefan-Boltzmann Law, and I am constantly seeing different quantities used. In some books I see "Intensity" and in others I see "Radiance", "...
-1
votes
0answers
25 views

Higgs boson -FREEZE

Why did the higgs boson freeze into the empty space of the universe? Please do tell how exactly we conclude that Higgs boson freeze and what does empty space signify here, is it free of matter and ...
-1
votes
0answers
16 views

The 555 nm light

How we know that the human eye is most sensitive to 555 nm light? Is there a way to measure it? Also why at 555 nm and 1/683 of a watt the human eye is most sensitive? Why is the number 683 taken and ...
1
vote
1answer
36 views

Density matrix of coherent state

The eigenstate of the annihilation operator $a$ is given by the state $a\mid \alpha \rangle = \alpha \mid \alpha \rangle$. In the Fock state basis, we can expand this state as $$\mid \alpha \rangle = ...
2
votes
1answer
45 views

Are there conserved quantities on the black hole horizons?

I am facing a conceptual difficulty while reading about black-hole(BH) horizons. Consider for simplicity a Schwarzchild(SW) BH, with a null hypersurface $\zeta$ denoting its horizon at $r=2M$ and let $...
1
vote
0answers
10 views

How is VLBI delay calculated, practically?

I’m working on a research project wherein we are trying to solve a problem very similar to VLBI delay. We have two radio receivers, and we know their locations. We also know at what time one receiver ...
0
votes
1answer
22 views

Spiral path of particle moving under circular force

Imagine a situation where a long masless stick is inserted through a ring, and fix one of the ends of the stick. Then, the system is given an impulsive force such that it starts rotating with an ...
0
votes
0answers
20 views

Beta negative (electrons) particles ionisation

Just wanted to know about how beta negative particles (electrons) ionise the surrounding particles. I've googled it and all I get is Alpha particles ionise most, beta lesser than alpha while gamma the ...
1
vote
1answer
25 views

How is the Wigner characteristic function defined?

When defining the Wigner characteristic function of a state represented by the density matrix $\rho$, I have seen various sources [including https://arxiv.org/abs/1110.3234] first define the Weyl ...
0
votes
0answers
18 views

Reconciling two descriptions of fluorescence

I am currently studying the textbook Infrared and Raman Spectroscopy: Principles and Spectral Interpretation, second edition, by Peter J. Larkin. Section 9. Selecting the Raman Excitation Wavelength, ...
0
votes
2answers
21 views

Solenoid Length In Inductance Formula

For a long solenoid, when the formula describes solenoid length, is it referring to the length of the wire wrapped around the magnetic core or the length of the core?
0
votes
0answers
19 views

Why do potential difference between the terminals of an ideal battery remains equal to its $Emf$ even if it is connected externally

In an ideal battery, the battery forces are equal in magnitude to the electric forces (the ones that are present when battery is not connected externally) and thus we conclude that E.M.F. ($\...
0
votes
2answers
26 views

Understanding the derivation of the formula for change in internal energy of a gas in an enclosed cylinder

The derivation: Let, there is $m$ mole of gas, $p$ amount of pressure, $v$ amount of volume, $T$ amount of temperature, and $U$ amount of internal energy. Now, $dQ$ amount of heat is supplied to this ...
1
vote
1answer
38 views

What is meant by the transverse nature of gravitational waves?

Gravitational waves, like the electromagnetic waves, are also transverse. By transversality of the EM waves, we mean that ${\vec E}\cdot\vec{k}={\vec B}\cdot\vec{k}=0$ i.e., the electric and the ...
0
votes
0answers
15 views

Why would one think that a solution of the time-independent Schrödinger equation is in the span of configuration state functions?

I am trying to understand why one would think that an $N$-body wave function would be in the span of antisymmetric functions that are simultaneous eigenvectors of each operator that commutes with the ...
2
votes
0answers
19 views

How can we prove that a non-linear equation of motion for a classical scalar field satisfies causality?

Let $\phi$ be a classical scalar field in $1+D$-dimensional spacetime with coordinates $(t,\vec x)$, and consder the equation of motion $$ \newcommand{\pl}{\partial} (\pl_t^2-\nabla^2)\phi+m^2\phi+ g\...
0
votes
1answer
28 views

How to determine a point's direction on a sinusoidal wave?

A transverse sinusoidal wave on a string moves from left to right. A snapshot of the wave is shown. Consider the red point on the figure being pointed to by the red arrow. Which way is this red dot ...
0
votes
2answers
24 views

How to increase temperature in a wooden box up to 495 degrees F? [closed]

How can I significantly increase the temperature in a relatively medium sized wooden box effectively to $495^\circ\ F$? The box is $3.5$ feet in height, $2.2$ feet in width, and $9$ inches in length. ...
1
vote
1answer
14 views

Why does the string of a simple pendulum need to be perfectly flexible?

The book says: "The string should be perfectly flexible, if we like to neglect the effects of different velocities of the different parts of the string during the oscillation." Can anyone ...
0
votes
0answers
24 views

Research in Black Holes [closed]

I am curious as to what computational coding languages I should learn in order to conduct proper research in the field of Astrophysics (Specifically Black hole research). I am familiar with Python, ...
0
votes
0answers
41 views

Is there a proof that a sum of torques equals a net torque?

I apologize for asking a question similar to this before, where in particular I asked for a derivation of Fr = Iα from the presuppositions of F = MA and the conservation of angular momentum. However, ...
0
votes
0answers
30 views

Is the fully connected Potts model exactly solvable?

Suppose that we have "spins" $s_1,\dots,s_N$, with $s_i=1,\dots,q$, and that our Hamiltonian is $$ H = -\frac{J}{2N} \sum_{i=1}^n \delta(s_i,s_j), $$ in which $\delta$ is a Kronecker delta....
1
vote
1answer
57 views

What was the motivation for thinking the weak interaction could be described by a Yang-Mills theory?

In some sense, describing the strong force using an $SU(3)$ Yang-Mills theory makes perfect sense: Yang-Mills theories describe massless bosons, of which the gluon is clearly a member, while the two ...
0
votes
0answers
39 views

Why doesn't finite field propagation speed contradict Gauss's law?

Imagine a charge sitting in space. It causes an electric field everywhere, with magnitude $\propto r_{old}^{-2}$ But now let's say we move the charge a little. This will change the electric field ...

15 30 50 per page
1
2 3 4 5
3292