0
votes
1answer
169 views

What are natural sources of longwave radiation

I am studying now the Earth radiation balance and I came across the question regarding the sources of the long-wave radiation on earth surface. The only source of theses wavelengths indicated in the ...
10
votes
3answers
968 views

What do the four components of Dirac Spinors represent in the Standard Model?

I've been trying to get my head around the formalisms used in the Standard Model. From what i've gathered Dirac Spinors are 4 component objects designed to be operated on by Lorentz Transformations ...
2
votes
0answers
136 views

What is the relation between N=2 super Yang-Mills and its twist

My question is what is the relation between N=2 super Yang-Mills and its twisted version topological field theory? After twisting N=2 super Yang-Mills, i.e. diagonally embedding $SU(2)'_R$ into $SU(2)...
1
vote
2answers
3k views

How to find the resultant of two forces? [closed]

I got this question in a assignment and haven't been able to figure out how to get to the correct result. A force of 6 newtons and a force of 10 newtons can be combine to form a resultant of ...
1
vote
1answer
681 views

Transparence of an infinite square well? [closed]

What does it mean by an infinite square well being transparent? I have been doing the calculation of the infinite square well and I came up with an answer $T = 1$ where $T$ for Transmission ...
2
votes
0answers
390 views

Calculating Electric Field from a Potential Difference w/o Charge

So here is my homework question: Two long cylindrical shells of metal (radii $r_1$ and $r_2$, $r_2 > r_1$) are arranged coaxially. The plates are maintained at the potential difference $\Delta\...
0
votes
2answers
213 views

A quantum finite square well

I have a problem with the argument of a finite square well. The stuff I read has mentioned that the Curvature " second derivative " is opposite sign of the wave function only when the E larger ...
3
votes
1answer
1k views

How does charge flowing between emf terminals reduce voltage difference?

I'm currently learning what electromotive force is and while reading my book's description of an ideal source of emf, I had difficulty understanding what these sentences mean: The nonelectrostatic ...
-1
votes
2answers
71 views

What temperature will create amorphous TiSi?

At what temperature will create amorphous TiSi? I think it's around 500 Celsius but I'm not sure.
2
votes
1answer
554 views

Will light bend in a circle on its own?

I found this article and I didn't understand it. I did get that they were able to bend light to 360 degrees. Does that mean if take a box that is completely empty, and shine a light into it, it will ...
0
votes
3answers
157 views

I'm having trouble wrapping my head around force, and thus acceleration, diminishing with a higher velocity when using a constant power

Here is an hypothetical situation I thought about that I don't understand. Let's say I have 2 identical rockets with a fixed power. These rockets start to race in the same direction using the full ...
3
votes
2answers
6k views

Resultant of two forces acting in the same line

I'm quoting the definition of Resultant of two forces acting in the same line from the book "A FIRST COURSE IN PHYSICS" one of whose authors is Robert Andrews Millikan: The resultant of two forces ...
2
votes
1answer
223 views

Spin tensor and Lorentz group operator in bispinor case

For infinisesimal bispinor transformations we have $$ \delta \Psi = \frac{1}{2}\omega^{\mu \nu}\eta_{\mu \nu}\Psi , \quad \delta \bar {\Psi} = -\frac{1}{2}\omega^{\mu \nu}\bar {\Psi}\eta_{\mu \nu}, \...
2
votes
2answers
239 views

Strange electrical circuit

This is a question I would like to have an explanation with: It's in this PDF, question 9. In that circuit, if switch 1 is closed, bulb A burns normally. If 2 is closed as well, do other lamps ...
4
votes
2answers
725 views

Will there be any force of attraction or repulsion between an electrified body and a non-electrified body?

Up to my knowledge an electrified (charged) body can attract a non-electrified (neutral) body. I thought this because, when we bring a charged (suppose negatively charged) body near a neutral one. ...
3
votes
1answer
236 views

Ghost Number Conservation

I've been reading about gauge theory quantization, and understand it mostly. The only thing I don't get is why people talk about "ghost number conservation". As far as I can tell, the ghost number is ...
2
votes
1answer
222 views

How to show that basis of space of Dirac gamma-matrices is given by following matrices?

How to show that 16 matrices $$ \mathbf E , \quad \gamma^{\mu}, \quad \gamma^{5} = \frac{i}{4}\gamma^{0}\gamma^{1}\gamma^{2}\gamma^{3}, \quad \eta^{\mu \nu} = -\frac{1}{4}\left(\gamma^{\mu}\gamma^{\nu}...
3
votes
0answers
111 views

Were fermions ever massless?

In a discussion of the Standard model and Higgs mechanism it was claimed that accordingly: "During an early phase of the cosmos all fermions were massless." I wonder whether this claim can be ...
2
votes
2answers
281 views

Infinitesimal volume using differentials

I don't understand why in some texts they put that infinitesimal volume $dV = dx dy dz$. If $ V = V(x,y, z)$ infinitesimal volume should be $$dV = \frac{\partial V}{\partial x} dx +\frac{\partial V}{\...
5
votes
0answers
535 views

Smallest minimum feature size possible for transistors printed by photolithography

I'm doing a project about Moore's Law, one of the subtopics I've come to is photolithography. The way I understand it is that the MOSFET transistors are currently printed on a silicon wafer by ...
2
votes
1answer
125 views

Why does taking a long step increase the chance of slipping?

Me and my friend were walking and it was raining. He didn't have any grip on the slippers so he took smaller steps to avoid slipping. We both were wondering why does taking a long step increase the ...
2
votes
2answers
558 views

twin paradox question

I'm trying to wrap my mind around the twin paradox, but I can't figure out this one problem from my textbook. It uses the relativistic Doppler effect to demonstrate how the paradox works. The first ...
2
votes
1answer
1k views

Calculate the latitude / longitude coordinates of the location where the Sun is at the zenith

There are plenty of resources showing how to calculate zenith and azimuth of the Sun when the time and the location are given. However, I need to calculate the location where the sun is at the ...
2
votes
3answers
567 views

Can I make a rod in the vertical plane move with its one end on the ground in a slanting position?

Consider a rod kept vertically on the ground. I keeps the rod in a slanting position making some angle with the horizontal. Can I now move this rod along the horizontal plane by applying a force at ...
0
votes
2answers
147 views

Length contraction as $v>c$

What would theoretically happen to an observed object's length (let it be a 5 meter line) moving at some speed greater than that of light in a straight path?
1
vote
1answer
310 views

Quantum Thrusters and Warp Drives [duplicate]

Any reservations about the potential of this (given in the link below/title above)? Does it seem like a helpless attempt or something which might have the potential of developing into something real? ...
1
vote
1answer
128 views

Accelerated charge inside sphere (again!)

Sorry to go on about this scenario again but I think something is going on here. Imagine a stationary charge $q$, with mass $m$, at the center of a stationary hollow spherical dielectric shell with ...
1
vote
1answer
265 views

Quantum randomness and brownian motion in biological systems, e.g., fertilization

I am looking for examples of physical indeterminacy impacting the macroscopic world. By physical indeterminacy, I mean physical sources of randomness such as quantum indeterminacy or brownian motion. ...
1
vote
0answers
100 views

EMF induced in a dynamo is by photons of permanent magnets?

i know little about the quantum field theory and also that the permanent magnets have there fields because of exchange of virtual photons across or around the ends. so when we take a dynamo and the ...
2
votes
2answers
603 views

Signs in proof of gravitation potential energy (GPE)

Proof of gravitational potential energy. Work done by gravity in bringing mass from infinity to a distance of $r$ between masses. When we use the integration formula and arrive at the answer we ...
-1
votes
3answers
1k views

In truth, only atoms and the void

I have a question about this motto used by Sean Carroll in his blog: In truth, only atoms and the void. Can you explain what this sentence means? My interpretation is that the sentence does ...
4
votes
4answers
2k views

Physical meaning of Impedance

So I have been thinking about the way impedance is defined for electrical systems, and the way it is derived. Even after looking through some websites, I cannot seem to grasp something, which every ...
3
votes
2answers
139 views

Why is charge $q$ symmetrically distributed?

Simple question: Why is charge $q$ outside symmetrically distributed? The material is a conductor.
4
votes
2answers
965 views

Is there scale by size of all discovered particles?

Atom: Neutron: Elementary particles: Is there scale by size of all discovered particles? From neutron and proton to electron and to boson? Compare to each other, like this I have found ...
1
vote
1answer
112 views

Obtaining a measurement very indirectly [closed]

While answering a question I came to reflect on the fact that in science experimental setups measure things indirectly. Example: the setup of the Pound-Rebka experiment. The amount of absorption was ...
13
votes
2answers
547 views

Can we quantize Aristotelian physics?

Aristotelian physics, shorn of whatever the historical Aristotle actually believed, is pretty similar to Newtonian physics. Instead of "An object in motion stays in motion unless acted on by an ...
0
votes
0answers
44 views

Factors defining interaction between atoms and molecules

Let's say we have a stuff that consists only of hydrogen (H), then we add a single atom of oxygen (O) and they interfere - we get a water molecule where atoms are arranged in a particular way. Then we ...
3
votes
1answer
518 views

Deriving Virasoro algebra question

I'm reading a book Lie groups, Lie algebras, cohomology and some applications in physics by Azcarraga and Izquierdo, and on page 347, when deriving the exact form of the central extension term I came ...
4
votes
2answers
343 views

How to understand the entanglement in a lattice fermion system?

Topological insulator is a fermion system with only short-ranged entanglement, what does the entanglement mean here? For example, the Hilbert space $V_s$ of a lattice $N$ spin-1/2 system is $V_s=V_1\...
1
vote
1answer
147 views

What confines atmosphere around earth?

Exactly the title. There needs to be a pressure to prevent gases from perpetually expanding, right? Bear with me, I'm not a physicist or studying to be one.
1
vote
2answers
515 views

naive question on Boltzmann equation and conservation laws

The Boltzmann equation in absence of external force reads: $\frac{\partial f}{\partial t} + \vec{v} \cdot \frac{\partial f}{\partial \vec{r}} = \left( \frac{\partial f}{\partial t}\right)_{coll}$ ...
4
votes
1answer
857 views

Why don't couple forces violate Newton's First Law?

If you have some random object at rest and you apply a couple to it, the net force acting on it is zero. However because a moment acts on it, it starts to rotate. So you had an object at rest, a net ...
1
vote
1answer
2k views

Calculating torque in 3D?

Say you have a sphere, and you have several torque vectors acting on it, all at different points. Say you have the vector (6i + 3j + 5k) originating from point A, and the vector (3i + 1j + 9k) ...
1
vote
1answer
426 views

Why does moment equilibrium at one point of an object mean the moment is at equilibrium for the whole system?

In class my prof said that when showing a system is at equilibrium it suffices to show that the moment at one point is zero. Why? Why does showing the moment at a point is zero imply the moment of the ...
2
votes
2answers
723 views

Why is moment dependent on the distance from the point of rotation to the force?

The formula for moment is: $$M = Fd$$ Where F is the force applied on the object and d is the perpendicular distance from the point of rotation to the line of action of the force. Why? Intuitively, ...
5
votes
3answers
746 views

Beam splitters and Mach-Zender interferometers

I have a question (my very first here) related to 50/50 beam splitters as used in the Mach-Zehnder interferometers (see for example the Wikipedia page). Let's concentrate on the input beam splitter: ...
1
vote
0answers
216 views

How to derive the Bethe stopping power formula

I need the derivation of Bethe formula for stopping power, but I can't see the corresponding paper to this matter. Application of Ordinary Space-Time Concepts in Collision Problems and Relation of ...
0
votes
0answers
131 views

why boundary condition in steady electric current?

when we electric field between two conductors in certain direction the current density should pass in its direction why current density direction change at boundary although the direction of electric ...
0
votes
1answer
69 views

Abstract vector form for integral of wavefunctions in subspace

In Landau, Lifshitz "Quantum mechanics (non-relativistic theory)" density matrix is given in the form $$\rho(x,x^\prime)=\int\Psi(q,x)\Psi^\ast(q,x^\prime)\text{d}q,$$ where $x$ is set of coordinates ...
2
votes
2answers
550 views

Why would mode-hopping occur as the current is changed?

If some diode laser is given an input current, why should we see mode-hopping if the current is changed?

15 30 50 per page