0
votes
0answers
3 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 ...
2
votes
0answers
7 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
0answers
4 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 ...
0
votes
1answer
16 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
1answer
13 views

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

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
18 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
28 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?
0
votes
0answers
17 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 ?
-5
votes
0answers
19 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
1answer
25 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
7 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
3 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
63 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
13 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
25 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
24 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
19 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
3answers
37 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
13 views

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

Why in the EXAFS experiments the light coming on the samples is monochromatic ? What would happen if a broad bandwidth hits a grating and then all the diffraction spectrum goes through sample and is ...
1
vote
0answers
11 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
154 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
47 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
24 views

How is the speed of light relevant to earth time when measuring the age of the universe?

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 mile per second to reach the distance ...
0
votes
2answers
34 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?
0
votes
0answers
13 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
30 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 ...
-4
votes
1answer
17 views

Frictional force

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
12 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
34 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 ...
0
votes
1answer
37 views

Why is the position space free particle wavefunction a function of momentum?

This is one of those little things that has always confused me. If someone said to you "in quantum mechanics, the eigenfunctions of a free particle are $\exp(ipx/\hbar)$" how would you know that ...
1
vote
0answers
35 views

Can gravity be blocked or augmented?

If gravitons (or some other quantum particle) are indeed responsible for the effect of gravity, can gravity be blocked, defected or trapped somehow? Is there any evidence that a gravitational field ...
3
votes
2answers
195 views

Double slit experiment with animals as observers

I was searching about the double slit experiment, reading and watching videos, etc. If I understood correctly, when they try to measure the photon it turns into particle. On the Youtube video ...
0
votes
2answers
17 views

Does Energy have a similar effect on time as Mass would when considering the gravitational field both exert?

I was thinking about light and the different frequencies. The higher the frequency the more energetic the photon. The higher frequency photon being more energetic seems counterintuitive when ...
0
votes
1answer
30 views

Tachyons and the light barrier

I read somewhere that if something breaks the light barrier, i.e. a tachyon, that it will take infinite energy to make it go slower than the speed of light. So, does that mean that the object will ...
0
votes
0answers
13 views

Choosing a term's sign — a rolling body question

https://prettygoodphysics.wikispaces.com/file/view/Rollin_and_Slippin.pdf In this link's first problem, top-spin is applied to a ball that slips; while the ball moves forward, it spins clockwise. ...
1
vote
0answers
12 views

Why can I see a light flicker when it's in my peripheral vision? [migrated]

When I'm looking at an old CRT monitor or a worn fluorescent lamp, but not directly in the center of my gaze, the light from it seems to flicker. When I focus my gaze onto the monitor or lamp, the ...
1
vote
0answers
41 views

How is partition function related to ordinary generating function?

Ordinary generating function can be used to solve combinatorial enumeration problems. Now if the energy levels are discrete, say $g_i$, and if one want to count how many ways one can add up $g_i$ ...
2
votes
1answer
44 views

Another cold-fusion reactor scheme :) Is it feasible?

I have this idea rolling in my head for quite a while, but lately I got really interested to know if it's even remotely feasible. I am complete novice to the field of nuclear engineering and cold ...
0
votes
1answer
11 views

What physical quantity can be deduced from an activity vs. time half-life decay graph?

I have a simple theoretical question regarding half-life decay graphs for radioactive substances. If the graph plots activity versus time (not mass versus time), then what physical quantity can ...
0
votes
1answer
23 views

How is a strength of a pull spread across two springs?

I started thinking about it when I came up with a puzzle which is probably way too elementary for this site, but it is hard for me to understand clearly. I just bought this small scale thing and I ...
1
vote
1answer
41 views

A single electron (and positron) annihilation, is my face melted?

To help clarify my understanding of scale in regard to microscopic particle energy levels (specifically, an electron), I came up with this thought exercise: What would happen if an electron and a ...
2
votes
1answer
16 views

Necessary and sufficient conditions for a function to be the Wigner function of state

For any quantum state defined with a continuous position, the Wigner function is a quasiprobability distribution on phase space. It has many properties, such as that its marginal are probability ...
0
votes
1answer
61 views

How to solve highly oscillating differential equation

The equation looks like: $$x''(t)+bx'(t)+c x(t)+dx^3(t)=0.$$ This is the motion of a particle in a potential $cx^2/2+dx^4/4$ with friction force $bx'$. In my case, the friction term is very small and ...
0
votes
1answer
21 views

How can I rearrange an equation to find a gradient for a capacitor?

If I plot R on the x axis and T on the y axis to give a straight line graph, and I am given that $V$ = $V_0$ * e^(-t/RC) then how can I prove that the gradient of the graph is equivalent to $C$ * ln3, ...
0
votes
1answer
20 views

What does an increased time constant of a capacitor do?

If a capacitor is being charged to any voltage, what effect would increasing the time constant have on it and if a graph of Charge Q/Time T was plotted to give a positive decreasing gradient, how ...
0
votes
0answers
9 views

What happens to magnetic $B$-field in a superconductor in the Bean model?

In the Bean model, as we start applying a magnetic field $H$ in the plane of a slab, the $B$-field inside the superconductor decreases linearly from each side, and at a sufficiently high field $H^{*}$ ...
0
votes
3answers
34 views

Object Pushed by Multiple Forces

If we have a general object and we have multiple forces acting on it at several points. Assuming we know the center of mass, mass and moment of inertia of the object: Will the object rotate only ...
-1
votes
0answers
19 views

How can I calculate percentage uncertainty?

If the percentage uncertainty of T is the modulus of 1/($lnV_0$-$lnV$) and the precision of $V$ and also $V_0$ is +-0.01V with peak voltage at $V_0$ = 12v and the statement $V$(ln$V_0$-ln$V$) ...
-2
votes
0answers
26 views

Why direction of Light is considered perpendicular to the motion of the objects in S.Relativity Equations?

When I look at Special Relativity Equations(Time Dilation/ Length Contraction), I see the direction of light is considered perpendicular to the motion of the object and then the Pythagoras theorem is ...
0
votes
1answer
31 views

Infinite Energies of a particle in a rectangular box

For a particle trapped inside a rectangular box of side lengths $l_x$ $l_y$ and $l_z$, the energies are ...

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