3
votes
1answer
96 views

What is $\phi$ as refered to in Guth 2007?

In this 2007 paper by Alan Guth discussing eternal cosmic inflation, he start's using a value $\phi$ on page 8. My understanding is that $\phi$ is the scalar field representing the dark energy of a ...
3
votes
2answers
659 views

Intro to Solid State Physics

I didn't see this listed on the books page so here it is. I'm currently in an introductory Solid State course, and we are using Kittel's book. I have been having a rough time with this book although I ...
5
votes
0answers
68 views

N=4 SYM in terms of N=1- SO(6) in the yukawa term

I'm trying to write N=4 SYM in terms of N=1 superfields. I have the lagrangian $$\mathcal{L}=\frac{1}{16 k} \int d^2 \sigma \text{Tr} \big[W^a W_a\big]+c.c+\int d^4\theta \text{Tr}\big[\bar{\Phi}^i ...
5
votes
0answers
45 views

Model for a thin metal/semiconductor junction?

Are there any books or articles that describe models for transport in a metal/semiconductor junction where the thickness of the semiconductor is less than the thickness of the depletion/accumulation ...
2
votes
1answer
199 views

Materials about S-matrix and S-matrix theory

What is the best book or paper to learn about analytical structures of S-matrix and S-matrix theory? I already know books as The Analytic S-matrix by RJ Eden, PV Landshoff, DI Olive, JC P and Quantum ...
1
vote
1answer
356 views

How fast does current flow? And the magnetic field? [closed]

A conductor carries 10 Amps, and generates a magnetic field $B$. How fast does it take for that current to flow from the wire throughout the entire circuit? And how fast does it take for the ...
0
votes
1answer
113 views

What is a “reference current”

Excuse me, I m not a physicist I am currently reading a paper about optimization on minimizing electrical energy in electrical vehicles. The paper talks about a "reference current" in a current ...
0
votes
0answers
407 views

Calculating Inertia Tensor with Parallel Axis Theorem

Say you have a solid you are approximating as n point masses at different points in a 3D space. Each point mass has a mass of 1. The origin is not the center of mass. All the points have location ...
2
votes
2answers
135 views

Is there anyway to use a scientific instrument to measure the density of electron around the atomic orbital?

Is there anyway to use a scientific instrument to measure the density of electron around the atomic orbital? Please list both old way and more modern ways.
1
vote
1answer
115 views

What kind of a particle has this mass?

I have a particle that has a mass around $(760\pm10)~MeV/c^2$ but I do not know what kind of particle it is. This links me to some tables that have data on all sorts of subatomic particles but it is ...
8
votes
3answers
618 views

Addition of spin angular momentum for massless particles

How do I add the spin angular momentum of massless particles, like photons, where only the transverse polarizations are allowed? If all three polarizations were allowed, this would be an easy ...
5
votes
1answer
400 views

What's the relation or difference between Lippmann-Schwinger equation and Dyson equation?

In quantum scattering theory, Green's Function is defined as [1] $$G_0(z)=(z-H_0)^{-1},$$ $$G(z)=(z-H)^{-1},$$ where $H_0$ and $H=H_0+V$ are separately non-interacting and interacting Hamiltonian. $V$ ...
1
vote
0answers
335 views

Block on block with friction [closed]

I couldn't find a similar question here - I'm guessing because it's kind of elementary. Lets say we have two blocks, $B_1$ and $B_2$, of mass $m_1$ and $m_2$ (respectively), where $B_1$ is directly ...
0
votes
0answers
111 views

More on the closed-form for a simple pendulum

I've learnt about the simple pendulum, and while the regular curriculum only uses the linear approximation of $\sin\theta$ to obtain $\ddot\theta+\omega_0^{2}\theta=0$. I tried to find out about a ...
2
votes
2answers
241 views

Acceleration of chairlift [closed]

So I'm struggling with this question, and am wondering if anyone can give me the right direction to go. For the sake of not cheating, I've changed the figures etc. I just need help on the approach. I ...
4
votes
2answers
768 views

Where is Strong Equivalence Principle stronger than Weak Equivalence Principle

In my note, the two equivalence principles are stated as follows Weak Equivalence Principle: Gravitational and inertial masses are equal. Strong Equivalence Principle: There is no observable ...
2
votes
1answer
6k views

Is radioactive decay spontaneous or random?

When the count rate of a radioactive isotope is measured, the readings fluctuate. Do the fluctuations demonstrate the random nature of the decay or the spontaneous nature? (This question was asked in ...
1
vote
0answers
113 views

The temperature dependence of the electron-hole (or particle-hole) continuum

In the theory of the electron gas, the particle-hole pairs are possible elementary excitations. I would like to know how the temperature T affects the particle-hole continuum which defines the domain ...
0
votes
1answer
124 views

What are the the characteristics of a standing wave? [closed]

May someone explain #24 from this picture? B is apparently the correct answer. Can any of the other answers be correct here? Isn't D also correct?
2
votes
2answers
2k views

Relative angular velocity and acceleration

Background: (Irodov 1.55) Two bodies rotate around intersecting perpendicular axes with angular velocities $\hat\omega_1,\hat\omega_2$. Relative to one body, what is the angular-velocity and ...
1
vote
2answers
446 views

Why does a microphone membrane only measure pressure and not particle velocity?

Microphones (e.g. condenser microphone) are assumed to have a voltage output proportional to the sound pressure at the diaphragm. If the operating principle is that the voltage output is proportional ...
0
votes
0answers
16 views

friction on a solid body due to another solid body

Suppose we have a block A and is moving on a rough horizontal surface with a velocity 60 m/s and another block B of same mass moving with velocity 5 m/s on same horizontal surface and suppose they ...
2
votes
1answer
259 views

Continuity and Blood Flow

Consider a tube with two different diameters (one section wider than the other). Because what comes in must go out (conservation of mass), the flow rate in the wider section must be the same as the ...
1
vote
2answers
168 views

Direction of future time cone inside Schwarzschild horizon

Following is the picture copied from enter link description here, illustrating the future time cone inside the Schwarzschild horizon. My question is, on the left side of $r=2M$, why must the time ...
1
vote
0answers
119 views

Momentum and position operators in Schrödinger representation

I was going through some intro notes on path integral (for QFT), and am stuck with this equation for position and momentum in Schrödinger (position) representation, $$ \hat{1} =\int ...
3
votes
1answer
334 views

Can a gravitational field be diluted or shielded? [duplicate]

An electromagnetic field can be diluted in a volume by using a dielectric. The polarization of the dielectric material results in the field decreasing in magnitude. Can a gravitational field be ...
2
votes
2answers
485 views

Electromagnetism duality theorem

Concerning Electromagnetism, textbooks often refer to the Duality Theorem. Sometimes it is presented like this: «Consider the Maxwell's Equations (with phasors) and a known field $\mathbf{E}_1$, ...
0
votes
1answer
299 views

How does a ducted fan suck in air?

I am thinking of a simple ducted fan with a single set of rotating blades, no stator vanes behind. If the effect of the fan is to raise the pressure of the air, how is there flow into the fan against ...
3
votes
2answers
70 views

Does Coriolis effect affect snowing?

Right now, outside is snowing. No matter what window I look from, the snow constantly for last few hours tends to fall to the right close to the window, and to the left close to the building across ...
5
votes
1answer
179 views

Where and how exactly does string theory and Q.E.D. use zeta function regularization?

In the video they mention it being used in many fields of physics inclusing String and QED theory. https://www.youtube.com/watch?v=w-I6XTVZXww But I remember reading somewhere that 1+2+3..=-1/12 is ...
0
votes
1answer
152 views

How to Extend Relaxation Methods for 2D Laplace Equation given in Jackson E&M to 3D?

In Jackson (3 ed) chapter 1.13 an outline is given for using relaxation to solve laplace equation in 2D. The general procedure in 3D involves minimizing the quantity $$I[\Psi]=\frac{1}{2}\int_V ...
1
vote
2answers
171 views

Visualising the magnetic field [closed]

How can we visualise the magnetic field?How to visualise magnetic field due to current carrying conductor having poles(like north and south for ordinary magnetic). Can we determine the north and the ...
7
votes
2answers
581 views

How can photons interact with anything?

I read photons do not age because they move at the speed of light. So when a photon interacts with my eyes, aren't they apart in space-time by the difference of the time in the frame of reference of ...
7
votes
1answer
645 views

Some conceptual questions on the renormalization group

I recently followed courses on QFT and the subject of renormalization was discussed in some detail, largely following Peskin and Schroeder's book. However, the chapter on the renomalization group is ...
5
votes
1answer
724 views

Direction of X-rays from x-ray tube

Typically anode of X-ray tube is at angle of ~45 degrees. Many images show that emitted X-rays are mostly perpendicular to electron direction. Is that correct? I had an impression that x-rays will ...
4
votes
1answer
660 views

Three integrals in Peskin's Textbook

Peskin's QFT textbook 1.page 14 $$\int_0 ^\infty \mathrm{d}p\ p \sin px \ e^{-it\sqrt{p^2 +m^2}}$$ when $x^2\gg t^2$, how do I apply the method of stationary phase to get the book's answer. ...
2
votes
0answers
151 views

How symmetry is related to the degeneracy?

I have several questions about symmetry in quantum mechanics. It is often said that the degeneracy is the dimension of irreducible representation. I can understand that if the Hamiltonian has a ...
1
vote
2answers
1k views

Simultaneous Charging and Discharging Capacitor

sorry if I sound little noobish. Though I have a fairly good understanding of physics, I sometimes don't understand the electrical aspects. Say there is a capacitor. This capacitor is expected to act ...
0
votes
0answers
50 views

Practical Resonance Derivation?

To my understanding, practical resonance occurs when the amplitude is at a maximum. Is this correct? Also I have looked all over for a derivation of the formula for angular frequency of practical ...
2
votes
0answers
64 views

Metric to describe an expanding spacetime from coordinates reflecting the perspective of a local observer

The FLRW metric describes the metric expansion of spacetime from the perspective of comoving coordinates. Given the way this metric is usually formulated, comoving distances stay constant, and the ...
2
votes
0answers
125 views

Is there any connection between “Lagrangian and Eulerian formalism of fluid” and “Heisenberg and Shrodinger picture”

Is there any connection between "Lagrangian and Eulerian formalism of fluid" and "Heisenberg and Shrodinger picture of Quantum mechanics"? Thanks!
1
vote
0answers
126 views

Does nonlocal theory violate causality?

Let's talk about two kinds of nonlocal theories. The first one frequently derives from integrating out part of the degrees of freedom to obtain a kind of effective theory. Probably, we get an integral ...
0
votes
0answers
29 views

Good First year physics lecture notes [duplicate]

My course textbook is Halliday fundamental of physics, this book is huge and since each week, they cover a lot of material in lectures (something about 6 chapters of the textbook), I find it hard to ...
1
vote
1answer
142 views

Does the transmission axis matter for sending polarized light through polarized glass?

If I have polarized light and I send through only one polarized glass plane, does the transmission axis matter, or will the intensity be halved no matter what.
0
votes
1answer
99 views

Could a super conductor actually be used to repel gravity? [duplicate]

I've always been interested in anti-gravity and how you could do it. I know that it would make space travel easier because less fuel would be required, but is it possible?
3
votes
1answer
82 views

Correct formula to express the potential generated by a single layer charge distribution

Assume that the closed surface $S$ encircles a volume $V$, and that a surface charge with density $\sigma$ ("single layer") is distributed over $S$. My question regards the electrostatic potential ...
4
votes
3answers
502 views

Thought experiment using quantum entanglement in position and its effects

Consider we have two atoms $a$ and $b$. They are entangled with each other in position and momentum, with some wavefuction describing them in position space that is $\Psi(x_a, x_b)$. This ...
3
votes
1answer
599 views

Biot-Savart Law from linear to volume current distribution

Biot-Savart law for a linear current distribution is: $\displaystyle \vec{B}=\frac{\mu I}{4\pi}\int\frac{\vec{dl}\times \vec{r}}{r^{3}}$. In the book that my professor uses says that if we have ...
1
vote
1answer
43 views

When is the speed specified for an object experiencing an exponential force?

So this is the question given in my text book: A particle of mass m is at rest at the origin at time $t = 0$. It is subjected to a force $F (t) = F_0e^{–bt}$ in the $x$ direction. Its speed ...
2
votes
1answer
77 views

Solving the 1-d time-independent Schroedinger's equation with an infinite boundary

In my introductory modern physics class we have examined time-independent solutions to the Schrödinger equation in 1 dimension. We looked at a few cases without finite boundary, e.g., free particles ...

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