0
votes
0answers
14 views

thermodynamics first law sign convention based problem [on hold]

Consider a (frictionless) piston-cylinder system. Initially, one mole of an ideal gas is present in the cylinder. The pressure and temperature of the gas are 1 bar and 300 K. A stirrer slowly ...
0
votes
0answers
14 views

How to find solutions to the gravitational potential metric h

I'm working on a problem in which a star of mass M1, radius R1 is surrounded by a shell of mass M2, , radius R2. I want to find the solutions to the gravitational potential h in the regions in between ...
1
vote
0answers
47 views

Energy-Momentum Tensor under Lorentz Transformation

In relativity, the symmetric energy-momentum tensor is given by $$ T^{ij}, $$ where $T^{00}$ is the energy density and $\frac{1}{c}T^{10}$ is the momentum density. Thus: $$ \left(\frac{1}{c}T^{00}dV, ...
-3
votes
0answers
39 views

Gauss Law - Variable Electric Field Perpendicular to Sheet [on hold]

So imagine a square sheet parallel to the x-y plane that has a perpendicular electric field (in the z direction) flowing through it such that $$E=\gamma x$$ where $\gamma$ is a constant value (lets ...
3
votes
1answer
150 views

Angular momentum depends on origin?

The angular momentum of a particle rotating about a point is given by $\vec{L} = \vec{r} \times \vec{p}$. Imagine a particle tracing a circular path on a flat table. If I put the origin of my ...
2
votes
2answers
181 views

Why are we blind for the era before the recombination?

At recombination, Universe became transparent to electromagnetic radiation after universe expanded enough to cool down to form neutral atoms. Before that, the matter plasma was effectively opaque to ...
1
vote
1answer
53 views

Gauss' law question

It's actually a teaching conflict at my school. They said that $$\text{Flux}=\frac{q}{\varepsilon_0}.$$ Say for a point charge at the centre of the sphere and let's say we not put water into the ...
1
vote
1answer
32 views

Properties of 3D waves

I have a few questions about 3D waves: Are all 3D waves types of electromagnetic radiation? Are all 2D waves mechanical?
0
votes
0answers
23 views

Law of Gauss. Electrostatics

I have seen on the internet that many times people assert that inside a cylindric condenser the electrostatic field is null due to the fact that the Gauss flux inside is null. But I wanted to make ...
1
vote
0answers
23 views

Charge distribution inside a parallel plate capacitor

I'm having difficulty deriving a known expression for the magnitude of the Electric Field within a parallel plate capacitor with applied potential difference $V$ and an immobile charge distribution ...
1
vote
4answers
71 views

Can't virtual images be put on a screen?

Apparently the plane mirror makes virtual images, and virtual images cannot be projected onto a screen. If you look below, it is? If the eye is basically a screen of rods and cones, then everything ...
0
votes
0answers
25 views

Forces, symmetry, and asymmetry

The concept of symmetry is one of the most promising and misunderstood concepts in physics. If one consider Hermann Weyl ("Symmetry"; ISBN-13: 978-0691023748), "As far as I see, all a priori ...
0
votes
1answer
23 views

Fraunhofer Diffraction using lenses

I've come across a question that I don't know how to tackle: An alternative way of observing Fraunhofer diffraction uses lenses to provide appropriate conditions. Sketch an optical configuration ...
0
votes
1answer
35 views

How does the process of protein denaturatation work? [on hold]

I know it's the proteins that somehow change their properties at some temparature. But what kind of change, in terms of molecule-level structure?
0
votes
1answer
24 views

What is the difference between virtual object and virtual image? [duplicate]

What is the difference between virtual object and virtual image?
1
vote
1answer
34 views

Converting between (abstract) linear operators and their position representations

Just as we have an abstract state vector $|\psi\rangle$ and its position representation $\psi(\vec{x}) = \langle \vec{x} | \psi \rangle$, how do we transform between a linear operator, say $H$, that ...
2
votes
0answers
24 views

Some question about symplectic transformation

I read Arnold's book Mathematical Methods of Classical Mechanics and come across with three problems in page 229. 1.Let $\lambda$ and $\bar{\lambda}$ be simple (multiplicity 1) eigenvalues of a ...
0
votes
0answers
20 views

What determines the speed required to pull a table cloth?

I was watching this show "Street Genius" on National Geographic and the host Tim Shaw demonstrated an experiment about Inertia, What he did was, He tied one end of a table cloth to a car through a ...
0
votes
0answers
20 views

how do you work out the direction of an eddy current

I find it very difficult to work out the direction of the eddy current, can someone please explain the steps in working out the direction of it? there is a following question; I dont understand how ...
0
votes
0answers
16 views

How to find out the electric field intensity between the plates of this Capacitor? [on hold]

I am preparing for my final and it seems that i cannot get the answer to this question, any tip will be really helpful thanks. Prove that the electric field intensity between the plates of Capacitor ...
0
votes
1answer
27 views

What is the relevance of potential energy as a concept?

As far as i understand, for an object to have a fixed quantity of potential energy, it must be in current equilibrium and have no net force applied to it (otherwise the potential would convert to ...
2
votes
1answer
37 views

An identity for spinor helicity formalism

I have a question about the spinor helicity formalism from arXiv:1308.1697 Denote the massless spin-1/2 fermions as Eqs. (2.10)-(2.11) in that paper $$v_+(p)= \begin{pmatrix} |p]_a \\ 0 ...
2
votes
1answer
39 views

What are threshold corrections?

As the title goes, what are threshold corrections in quantum field theory? In particular, I would be glad if a good reference is provided. Standard QFT books such as Peskin, Weinberg, etc seem to ...
1
vote
1answer
39 views

Branch cuts in two-point function

The propagator of a QFT is known to have a branch cut as a function of the (complex) external momentum. The branch point (as done by, say, Peskin & Schroeder in eqn.7.19 section 7.1) is ...
0
votes
0answers
69 views

How come that an Infinite universe will collapse under gravity?

In this PSE post the issue is about the stability of an infinite universe under Newtonian gravity. Here I'will drop the Newtonian constraint because we know of the finite speed of interactions and I ...
-2
votes
0answers
24 views

Calculating power [on hold]

I need some help and explanation with solving this question: What is the power required to give a body of mass m a forward acceleration of a when it is moving with velocity v up a frictionless ...
1
vote
1answer
46 views

Is cosmic background radiation absolute [duplicate]

Now that we don't have permeating Ether anymore, why don't we consider the omnipresent Cosmic background radiation in place of it? and measure Speeds with respect to the CMBR? In that way an object ...
1
vote
1answer
21 views

Is work done by sound wave on air particles?

Is it possible for sound wave to do net work on air particles? As in can a sound wave make the air move in one direction so that it can for example move a sail boat ? I think since molecules gyrate ...
-2
votes
0answers
172 views

How long would it take to get to Kepler 189f? [on hold]

I just read a news story about a planet that might be Earth-like called Kepler 189f. It is 500 light years away. How long would it take to travel there in a space ship, from the travelers reference ...
0
votes
1answer
45 views

Kronecker delta in inertial tensor

I feel confused in (11.9) how does the book prove the following identity: $$\sum\limits_{i} w_{i}x_{\alpha,i} \sum\limits_{j} w_{j}x_{\alpha,j} = ...
1
vote
0answers
28 views

What is the meaning of space-time curvature?

What is the difference between the Space-time curvature and Space curvature ?
3
votes
1answer
52 views

What does energy represent in $E= mc^2$?

Due to energy-mass equivalence, any object with mass can be said to have a corresponding amount of energy. So in a 5kg object there are 450,000,000,000 joules. A joule as i understand it is the ...
4
votes
0answers
38 views

Is $\overline{\psi_{L}^{c}}\psi_{R}^{c}=\overline{\psi_{R}}\psi_{L}$ true for two different spin 1/2 fermions?

In the context of seesaw mechanism or Dirac and Majorana mass terms, one often see the following identity $$ \overline{\psi_{L}^{c}}\psi_{R}^{c}=\overline{\psi_{R}}\psi_{L}. $$ Here, I am using 4 ...
0
votes
1answer
32 views

Is there any significance to the negative sign on this speed?

A girl is riding a bicycle along a straight road at constant speed, and passes a friend standing at a bus stop (event #$1$). At a time of $60$ s later the friend catches a bus (event #$2$) If the ...
1
vote
1answer
21 views

What's the total Cosmic Microwave Background energy?

This is a part of my wider attempts at accounting matter in the observable universe. The total light ever emitted by stars and other space objects is capped around 1% of baryonic mass (in energy ...
2
votes
0answers
15 views

Off-diagonal terms of the Husimi $Q$ function?

The Husimi $Q$ function of a quantum state $\rho $ is defined as $ Q (\alpha)=\langle \alpha \vert \rho \vert \alpha \rangle $, where $\alpha = (x, p) $ is a phase space coordinate and $\vert \alpha ...
0
votes
0answers
14 views

Does dark energy bring both universe curvature and expansion?

These are Basic questions . 1,Does dark energy bring universe curvature for both sides of the Minkowski space's future and past to shape the de-sitter space ? or just the single side curve ? What it ...
-1
votes
0answers
25 views

2nd Law of Thermodynamics and Cosmology

Does the 2nd law definitely show the universe had a beginning and refute the idea of an eternal universe?
0
votes
0answers
18 views

Will it ever be possible to observe the cosmic neutrino background?

Is there any foreseeable technology which would facilitate the direct observation of the cosmic neutrino background? Would the ability to warp spacetime have any application here?
0
votes
0answers
8 views

Friction in Water - Conservation of Energy [on hold]

A 57.0 kg diver dives from a height of 15.0 m. She reaches a speed of 14.0 m/s just before entering the water. What is the force of friction underwater if she reaches a depth of 2.5 m before ...
0
votes
1answer
19 views

Conservation of Energy - A Golfer Question [on hold]

A golfer strikes a ball in a parabolic arc at and elevated green (3.5 m above launch). The ball leaves the player's club at 37 m/s and an angle of 40 degrees. The mass of he ball is 0.043 kg. ...
11
votes
6answers
955 views

Why are sine/cosine always used to describe oscillations?

What I am really asking is are there other functions that, like $\sin()$ and $\cos()$ are bounded from above and below, and periodic? If there are, why are they never used to describe oscillations in ...
2
votes
1answer
43 views

Goldstone couple to conserved current

The Goldstone in spontaneous symmetry breaking problem couples naturally to the associated conserved current of the broken symmetry. How can I see a rigorous (mathematical) derivation for that?
0
votes
2answers
55 views

When pressure is exerted on parallel hydraulic pistons, do they start extending at the same time?

If there are two hydraulic cylinders connected in parallel, each with a different load (shown in the picture below), will they start extending at the same time? I'm having a disagreement with my ...
0
votes
1answer
79 views

Can “state” be considered a 5th dimension?

I searched for an answer to this question on Google but just found articles that mention either string theory or a 5th dimension in passing (such as Maxwell equations as they relate to Riemann ...
0
votes
1answer
45 views

Studying Quantum Electrodynamics?

As an electrical/computer engineer, I already have a relatively thorough understanding of classical electromagnetism. From what I understand though, classical EM is only an approximation to quantum ...
1
vote
1answer
41 views

What is the electric field between and outside infinite parallel plates?

I know that Gauss's law says $$\oint_S {\vec{E} \cdot d\vec{A} = \frac{q_{enc}}{{\epsilon _0 }}}$$ and that because $\vec{E}$ is always parallel to $d\vec{A}$ in this case, and $\vec{E}$ is a ...
0
votes
1answer
16 views

Simulating electrical sublimation of aluminium foil

When i apply high voltage (through a capacitor bank) across an aluminium foil, it gets converted into plasma. I want to simulate this process and study the properties of the plasma produced ...
0
votes
1answer
8 views

Thermal resistance of thermal interface materials?

Thermal conductivity are often used for surfaces between the computer chip and the heat sink to increase heat transfer and they want high thermal conductivity to decrease the thermal resistance. By ...
0
votes
1answer
45 views

Does all information in the universe come from the observer?

In absence of the observer any system undergoes unitary evolution, that is reversible evolution without entropy change. It is believed that the initial state of the universe had very low entropy, ...

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