0
votes
0answers
2 views

The magnetic field between two intersecting cylinders

"Consider a cable of infinite length whose section has the form of two intersecting circles of same radius $a$. The first part is then a cylinder of constant volume current density $J$ along the ...
1
vote
1answer
21 views

Are there other less famous yet accepted formalisms of Classical Mechanics?

I was lately studying about the Lagrange and Hamiltonian Mechanics. This gave me a perspective of looking at classical mechanics different from that of Newton's. I would like to know if there are ...
-3
votes
0answers
28 views

Did God have enough water to flood the earth during Noah's time? [migrated]

In Genesis 7:11-20, we read how God destroyed the living beings on earth--save for Noah's family-- using flood. In the six hundredth year of Noah’s life, on the seventeenth day of the second ...
0
votes
1answer
24 views

Why do $S_x$ and $S_y$ flip up/down spin states but $S_z$ does not?

By using the notation $S\lvert s,m_s\rangle$, such that $\bigl\lvert\frac{1}{2},\frac{1}{2}\bigr\rangle=\lvert+\rangle$ and $\bigl\lvert\frac{1}{2},-\frac{1}{2}\bigr\rangle=\lvert-\rangle$ we can ...
-2
votes
0answers
12 views

Is a black hole a 3D hole? And doesn't it pull into the 4th dimension?

Hear me out here please: A body on a line (a 1-D world) causes a warp in the line, i.e. a curve (2-D) A body on a plane (a 2-D world) "sinks", causing a warp in the plane, i.e. a pit (3-D) Then does ...
0
votes
1answer
11 views

Can information travel inside to outside the event horizon?

Lets suppose I am an immortal man and I have a very strong and long stick. We know that information cannot travel inside to outside the event horizon and as far as I know there is nothing special ...
5
votes
0answers
39 views

Why don't we have logarithms or exponentials of the fields in the Lagrangians?

All tbe Lagrangian densities I have seen have always been polynomials of the fields. Is this a coincidence or is there a reason forbid, say, Lagrangians with logarithms or exponentials of the fields?
0
votes
0answers
7 views

Regge trajectories for higher spins

I have read that Regge theory did/does predict higher spin meson states, but that at higher spins the data becomes fuzzy for spins greater than 4. Why is this so? In the book "A Brief History of ...
0
votes
1answer
18 views

Why isn't the magnitude of the electric field in a circuit zero?

I've been re-reading my knowledge of circuits and how current flows as well as the surface charge distributions in the steady state, since it's been quite some time and we've just started studying ...
0
votes
0answers
19 views

Deriving the Maxwell-Boltzmann distribution

I am considering the microcanonical ensemble. The probability of being in a particular micr?ostate is, $$p_{E,\mathbf{x}}(\Gamma) = \begin{cases} \frac{1}{\omega(E,\mathbf{x})} & ...
0
votes
0answers
15 views

can one distinguish between superposition with randomized phase and classical probability?(an experiment)

I hope that the following experiment will help me understand the topic better. Let's say my friend is sending me photons via two channels and he is doing it in one of the following two ways: he is ...
2
votes
1answer
31 views

Resources for introductory *quantum* statistical mechanics

I am currently struggling to understand my basic introductory course on quantum statistical mechanics and I have done a basic course on single particle quantum mechanics. I was wondering whether ...
0
votes
0answers
11 views

Fraction of kinetic energy carried by neutrons after D-T Fusion

I am trying to answer the following question: Ignoring the initial kinetic energy and momentum of both particles in a D-T fusion reaction calculate the fraction of the released kinetic energy ...
0
votes
1answer
53 views

Physics behind this drunken ball

I am trying to understand the physics behind this drunken ball: There is a wight inside the ball as he mentions, but where, at what position ? ...
0
votes
2answers
35 views

Varying wrt metric

I saw people write $\frac{\partial( F^{ab} F_{ab})}{\partial g^{ef}}$ as $\frac {\partial (g^{ca}g^{db}F_{cd}F_{ab})}{\partial g^{ef}}$ in a way that exposes the dependence on the metric. but ...
0
votes
1answer
15 views

Units for displacement current density

The displacement current density, $$\mu_0 \epsilon_0 \frac{\partial \textbf{E}}{\partial t}$$ has units of (N/A^2) (C^2/Nm^2) N/Cs = Ns^2/(Cm^2) which is not the same for current density: C/sm^2 ...
0
votes
0answers
10 views

Electric field on conductor surface

Having searched around I came to the conclusion that the electric field on the surface of a charged conductor is undefined as in there is a discontinuity but is there a way to explain it intuitively ...
2
votes
1answer
28 views

Can a magnifying glass work on EM radiation other than visible light?

A magnifying glass is a convex lens which allows us to bend visible light, thus the image of the object appears larger. My question is, can a magnifying glass work on the rest of the electromagnetic ...
0
votes
0answers
32 views

Summing over quantum states

For a system of $N$ identical particles we deal in quantum mechanics with wave functions $\langle \{\mathbf{r}_i \} \mid \Psi \rangle=\Psi(\mathbf{r}_1,\dots,\mathbf{r}_N)$ from which determine the ...
-3
votes
1answer
25 views

Why is it necessary to supply constant electricity to make a laser work?

As we know that in lasers there are excited atoms. When energy is provided in the form of light, heat or electricity to these atoms, these excited atoms after sometime go to a lower state of energy ...
0
votes
0answers
15 views

Is it common for hot objects to have more black-body-like spectrum for higher frequencies?

I'm comparing spectral output of an incandescent light lamp, for which the spectrum is given by manufacturer. Namely, I took the color temperature given in the specifications and inserted it to ...
1
vote
0answers
19 views

Is there a Ramond vacuum for real fermions?

When studying the CFT of a complex fermion $\Psi$ we know that if it's periodic, ie if $$\Psi(\sigma_1+2\pi,\sigma_2)=\Psi(\sigma_1,\sigma_2)$$ then there is a doubly degenerate Ramond vacuum which I ...
3
votes
4answers
63 views

Different kinds of energies in the form of $\frac{a_1a_2^2}{2}$

It seems to me that the energy of some kind frequently takes the form $$\frac{a_1a_2^2}{2}$$ Where $a_1$ and $a_2$ are some variables. So, for example, kinetic energy has $m$ and $v$; rotational ...
0
votes
1answer
22 views

Can we create plasma with other things except gas?

In my school book its written on how plasma is created and it is said that we can create plasma by ionizing a gas but i have heard that plasma can be created even from liquids like water and also from ...
1
vote
1answer
37 views

Why the image is being formed at the surface?

Last week I encountered a very cool optical phenomenon. A photo was sandwiched between the two glass plate to make the paperweight. The cool part is the picture seems to have been pasted on the top ...
1
vote
0answers
18 views

What causes “stringy” melted cheese (and similar behavior in other materials)? [migrated]

I was wondering about this. What is the physics underlying the "stringy" consistency of melted cheese? That is, when the melted cheese is hot, and it is pulled apart, it forms strings of cheese. This ...
0
votes
1answer
28 views

Speed, weight and force

If a road roller of weight $W$ is rolling on the road at the speed of $X\,\mathrm{kmph}$, how much force does it apply on the surface of the road (considering a sampled surface of the same size as ...
-1
votes
1answer
48 views

How do you become a theoretical physicist? [on hold]

Is there a specific subject at university called "theoretical physics" or do you get a PhD in Physics and then if your job involves theory you are considered a theoretical physicist?
-1
votes
0answers
26 views

D-T fusion reaction releases 17.6 MeV of energy

How to show that the D-T fusion reaction releases 17.6 MeV of energy ? I am only getting it as a fact but how can I prove it ?
-3
votes
0answers
21 views

Which units are affected if we double the unit of length/velocity or force? [on hold]

If the unit of length: $m$, velocity: $v$, and force: $N$ is doubled, which of the following options is correct? (changes in other unit) unit of time is doubled unit of mass is doubled unit of ...
1
vote
3answers
52 views

Why U235 over U238?

There are 3 isotopes of uranium that can be found in nature[1]: U234, U235 and U238. For a chain reaction to last there must be a high amount of neutrons contents and by comparison, U238 contains 92 ...
-1
votes
1answer
9 views

is it possible to measure mains induced current flowing from my body to ground?

I can measure a voltage that is induced on my body via an electromagnetic field from a 50hz ac source, and would like to know if it's possible to measure the induced current on my body, if any, when ...
0
votes
0answers
4 views

Non Combustion Atmospheric Propulsion [on hold]

Is it possible? With electric motors set aside, what are the viable options for propulsion?
1
vote
1answer
226 views

Motivation for isospin

I am having trouble understanding the point of isospin. Why do we need isospin? The rationalization that protons and neutrons are similar doesn't make sense to me.
0
votes
0answers
21 views

Why 'free energy' can contain different amount of information in different settings, and what's their connection to phase transition?

I have seen 'free energy' arising from several contexts in very different forms, and each contains different amount of information (as a number, 1D function, 2D surface, etc). For example free ...
0
votes
1answer
32 views

Photons and EM Fields

I started learning the basic ideas of QFT in an intuitive manner ( withouth any math, only with mental videos and pictures ) some days ago, and i'm finding it completely beautiful [ the idea of ...
1
vote
2answers
25 views

How to explain the momentum exchange of two solid particles collision at molecular scale?

Here is my question: assume two solid sphere collided to each other in vacuum, at macroscopic, it can be explain by Newton's law. But at molecular scale, does the surface atoms touch to each other or ...
1
vote
0answers
24 views

The relation between electric and magnetic potential equation

Use the principle of duality to derive: $$\textbf{A} = \frac{\mu e^{-j\beta r}}{4\pi r}\int\int_S\textbf{J}_s\, e^{j\beta\, \hat{\textbf{r}}.\textbf{r}'}dS'$$ from this $$\textbf{F} = ...
0
votes
4answers
78 views

Why aren't we affected by radium?

1)We have radium clocks, watches, wrist bands and many things which glow because of radium but we know that radium is radioactive so why isn't it harmfull for us when in bands, watches etc. 2)Does it ...
0
votes
0answers
21 views

What is the reason that EXAFS are done with monochromatic x-ray light?

Why is the light incident on the samples in EXAFS experiments monochromatic? What would happen if a broad bandwidth hits a grating and then all the diffraction spectrum goes through the sample and is ...
1
vote
0answers
12 views

Mean value of number of molecules of a gas inside a volume

I'm trying to solve this problem in Statistical Mechanics but I'm not sure if my reasoning is right. The problem is as follows: we have a certain region with volume $V_0$ containing $N_0$ molecules of ...
2
votes
1answer
261 views

Antineutron repelled by gravity?

I was reading an old post, Can gravity be shielded, like electromagnetism?. One of the responses had this comment. There are some experiments trying to measure whether antiprotons ( antimatter) ...
1
vote
2answers
57 views

Why is earths gravitational pull only at its center?

Does acceleration due to gravity remain constant wherever I go in and on the earth?
0
votes
0answers
44 views

Does the universe have a different age to different observers?

Although I understand that the universe is approximately 12 billion light years wide, and that may mean that it took the light photons 12 billion years at 186,000 miles per second to reach the ...
0
votes
2answers
36 views

What is the pressure of falling water?

Imagine a breaking wave 10m high. The wave breaks onto a beach. What is the maximum pressure created by the wave on the beach, ignoring effects such as might be cause by air?
-1
votes
0answers
16 views

How to cancel $\mathcal{N}_3$ in the hierarchy equations for the neutrino moments? (Dodelson, eq (6.107))

I was trying to understand the Boltzmann equation (B.eq) for massless and non-interacting neutrinos, principally to solve one datail in the exercise $6.2$ of Dodelson. Given the Beq for neutrinos in ...
0
votes
3answers
31 views

When moving from one position to another at a constant velocity, how does the conservation of energy hold?

I know that this might be a duplicate question, but I have not found any satisfactory answers that clear up my lack of understanding. Here is my question. Say a sloth hangs on a tree in the middle of ...
-3
votes
1answer
18 views

Frictional force [on hold]

a box of banana weighing 40N rests on a horizontal surface. the coefficient of static friction between the box and the surface is 0.4 and coefficient of kinetic friction is 0.2. a. if no horizontal ...
0
votes
0answers
13 views

What is the maximum net force of surface tension per gram of water?

I've always wondered how much force water exerted through surface tension. By maximum I mean the theoretical pulling/attracting power. Also, what would happen if you raised or lowered the power? ...
0
votes
1answer
36 views

assuming $kT=1$ in $Z=\sum e^{-H}$ and $F=-lnZ$?

Some statistical physics book use: $Z=\sum e^{-H}$ and $F=-lnZ$ as defination for partition function and free energy. I think they should be $Z=\sum e^{-\frac{H}{kT}}$ and $F=-kT lnZ$ Are they ...

15 30 50 per page