All Questions

1
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1answer
78 views

Schrödinger Equation with Imaginary Potential

I am trying to solve the following equation (in 1D) and stuck in the middle of the way. Here's the equation: $$i\frac{\partial\psi}{\partial t}=C\cdot\frac{\partial^{2}\psi}{\partial x^{2}}+iD\cdot\...
0
votes
0answers
19 views

What happens when a photon hits a particle (radiative heat transfer, photoelectric effect)?

By relating temperature to particle motion, the kinetic theory of gases gives an intuitive explanation of conductive heat transfer; faster particles collide with slower ones to transfer kinetic energy....
0
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0answers
20 views

Applying law of Biot-Savàrt when magnetic field passes through different materials

Hi I'm trying to calculate the power of a magnetic field outside a coil winded around a electric steel core. The point I'm trying to measure is on the axis of the coil but 2 mm outside the electric ...
0
votes
0answers
13 views

Calculating the shielding required to protect against radiation at lunar orbit

I am attempting to calculate the thickness needed to protect the crew inside a space module at the Lunar Orbit with Lithium Hydride from X and Gamma Rays. How would I calculate the thickness of Li-H ...
2
votes
1answer
61 views

What is complex frequency? [on hold]

I am learning EE, and about complex frequencies, but what is its physical meaning? What is it used for? Why is it? And only happen in the laplace transform?
0
votes
1answer
20 views

How to calculate mass proportions of each compound in air?

We know average volume proportions between compounds in dry air. Here are the more important (in terms of proportions) ones: How can we calculate mass proportions between these gases? I'm ...
1
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0answers
41 views

Length Contraction of a rotating object

When observing an object, such as a spinning ring, what velocity is used to calculate its length contraction? I know it depends on the observer, but let's say theoretically an observer is just ...
0
votes
2answers
49 views

What happens to the energy of an absorbed photon?

Photons are electromagnetic wave fields that travel at the speed of light. When they are absorbed by an object, their momentum and energy is transferred to the absorbing object. What is that ...
0
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1answer
23 views

Thermal radiations

everything having temperature above 0 k emits radiation. But those radiations depend upon temperature of the body and not on nature of the body. Why thermal radiations are not material dependent?
-1
votes
1answer
50 views

Does the heat created by gravitational energy cause Infinite energy? [on hold]

As everyone knows there is this thing called geothermal energy. Many people in Iceland and such countries get their energy from geothermal plants. My question is since some of the heat in the earth is ...
1
vote
1answer
36 views

Proof of equipartition theorem for $i$ not equal to $j$

The generalized equipartition theorem (where variables need not be quadratic) states that if $x_i$ is a canonical variable (position or momentum variable), then $$\left\langle x_i \frac{∂H}{∂x_j}\...
2
votes
2answers
60 views

Resistance of an object with arbitrary shape

Suppose to have a conductor with a non-trivial geometry, like the one in the picture: The shape does not really matter for this question, as long as you suppose to have at least one "hole" in the $z-...
-4
votes
0answers
21 views

Quarterback Question [on hold]

Quarterback passes football at 8.00m/s at angle of 31.5 degrees above horizontal. How far does it travel horizontally (assuming it is caught at the same height it is thrown)?
3
votes
1answer
118 views

Is it possible to find dry ice crystals lying around the base in Antarctica?

Dry ice sublimates at -78.5°C, while the lowest temperature registered is about -89.2°C around the Vostok station in Antarctica. Imagine a person living on that station on that day (or night, since it ...
0
votes
1answer
6 views

Lateral (bending) stiffness of a helical compression spring

Does a helical compression spring have uniform lateral (bending) stiffness throughout its length? Suppose I exert a force radially along a certain height of the spring, and that force rotates along ...
-1
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0answers
10 views

Magnetic Dipole Moment of cylindrical current distribution [on hold]

In this attached image, i have to find dipole moment as it is part of my homework assignment
0
votes
1answer
17 views

How to calculate mass of a gas mixture knowing its volume, molar mass and pressure?

I have a gas mixture of volume $V$, molar mass $m$, pressure $P$. I need to calculate its mass $M$, but all formulas I found get in the loop as pressure formula requires density, which then ...
-3
votes
0answers
46 views

Is it 4-D or 11-D Universe? [on hold]

I know these are just theories, but I wish to know which of the two are the most used right now to speculate how many dimensions of space and time our universe has. I heard that in the standard ...
0
votes
0answers
12 views

Relationship between polarization charge density and free charge density

I have concluded that in a uniform dielectric, volume free charge density $\rho_0$ and volume polarization charge density $\rho'$ satisfy $$ \rho' = \frac{-(\epsilon - \epsilon_0)}{\epsilon}\rho_0 $$ ...
-1
votes
0answers
46 views

Suppose that we are living in an Anti de Sitter space: which open problems would be solved? [on hold]

It is often said that we live in a de Sitter (dS) universe. This is because the standard theory of cosmology is descibed in a four dimensional de Sitter space-time. On the other hand, there are some ...
1
vote
3answers
55 views

Inertial and non-inertial reference frames

My book states that: A reference frame attached to earth is not inertial because it is revolving around the sun and it is rotating about its own axis. Don't we need a specified observer's frame ...
2
votes
2answers
117 views

Curl and circulation of a vector field that is ill-defined at the origin: any interesting physical effects?

In the cylindrical polar $(\rho,\phi,z)$ coordinate, suppose the velocity field in a liquid is given by $$\vec{v}=\frac{K}{\rho}\hat{e}_{\phi}, \qquad K=\text{constant}.\tag{1}$$ It can be easily ...
0
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0answers
14 views

How to calculate the transition energy between $^2P$ to $^2S$ and $^2D$ to $^2S$ for sodium?

It's been known how to calculate the Zeeman effect. However how to calculate the transition energy between $^2P$ to $^2S$ and $^2D$ to $^2S$ for sodium($Z=11$)? ($^2P$ here meant term symbol ignored ...
0
votes
1answer
27 views

Doubt in the derivation of the relation between Young's modulus and Modulus of rigidity

Please refer to the image attached. My doubt is marked in red. What i don't understand in this part of the derivation is that how and why is the extension and compression is equivalent to a shear ...
3
votes
1answer
35 views

Divergence of $ \frac{1}{s}\hat{s}$ in cylindrical coordinates

In Griffiths' electrodynamics, the divergence of $\frac{1}{r^{2}}\hat{r}$ is evaluated in spherical coordinates to be $4\pi\delta(r)$. I encounter the same problem in case of $\frac{1}{s}\hat{s}$ ...
1
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0answers
14 views

Cast Caldeira-Leggett master equation to Lindblad form

Consider a Brownian motion particle, whose motion is described by $\frac{d}{dt}\rho_{S}=-\frac{i}{\hbar}[H_{S},\rho_{S}]+\sum_{i,j}a_{i,j}(F_{i}\rho_{S}F_{j}^{\dagger}-\frac{1}{2}\{F_{j}^{\dagger}F_{...
-1
votes
2answers
52 views

Relativity of Simultaneity Confusion [on hold]

An electron is emitted from a nucleus at a speed of $0.975c$ as observed in a laboratory frame of reference. The electron is detected at a distance of $0.800$ $m$ from the emitting nucleus as measured ...
0
votes
0answers
22 views

How much conduction, radiation and convection influence in a thermos flask?

It has been thoroughly repeated that thermos flasks prevent heat loss by minimizing heat conduction, radiation and convection from the bottle to its ambient. This has been answered in this SE. However,...
2
votes
0answers
25 views

Computation of Feynman integrals in terms of Chen Iterated integrals

One of the techniques used to compute Feynman integrals in dim-reg is the so-called "differential equations method". Exploiting integration-by-parts identities (linear functional relations between ...
0
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0answers
34 views

Einstein equations algoritms solutions [on hold]

My question is, is there an Einstein equation's calculation algorithm, and what is Einstein's 10 equation system?
1
vote
2answers
82 views

Relativity Confusion

In the time dilation formula $\Delta t=\gamma\Delta t_0$, I am confused about what $\Delta t$ and $\Delta t_0$ measure. If we have two people, Tom and Bob, moving at constant velocity relative to ...
0
votes
2answers
90 views

How propulsion in the “HELPING HAND” NetFlix episode works? *SPOILER*

I watched the "HELPING HAND" episode in NexFlix, and the protagonist is drift in space, every second she is more far from her ship, when her tank is out of oxygen, she throw her glove to make a ...
-2
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0answers
15 views

Fly wing velocity question [on hold]

A fly beats its wings at a frequency of 1200 Hz. if the expansion and contraction of the wing muscles of the fly exhibits simple harmonic motion, the angular displacement of each wing of the fly also ...
0
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0answers
42 views

Why does current not increase when the voltage increases in this case? [migrated]

When talking about BJT transistors, a very common graph is the one shown below, that plots (VCE,IC) as an ascending function. As far as I know, the BJT manages VCE so that IC is beta times IB, being ...
1
vote
0answers
17 views

What are dark excitons and how to find them?

I am reading about excitons and I encountered a few times the term "dark exciton" but I have a hard time finding a good definition. I tried to google it but I only find scientific articles where the ...
1
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0answers
21 views

What exactly sets the scale in Fusion power plants?

In fusion power plants, larger devices are said to achieve fusion more easily, next step tokamaks like DEMO are even larger than ITER. In a quantitative way, what exactly isn't scale invariant in a ...
0
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0answers
21 views

The ideal shape of a plano-convex lens

What's the type of the ideal shape of a surface of a plano-convex lens to focus a parallel beam at the point? Considering the lens turned its flat side to a beam. Surely it must be aspheric: ...
0
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0answers
7 views

What is the twist 2 sector of nucleonic parton distributions?

I am on the evolution of transversity distributions in QCD. And in the papers everyone talks about twist 2 sector and leading twist corrections. I can't find anything about twist. Do they talk about ...
0
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0answers
41 views

Assumptions and limitations for ideal gas

Assumption: In the assumption for ideal gas law, it is stated:"The time it takes to collide is negligible compared with the time between collisions." For, this assumption, can i just say there is only ...
1
vote
1answer
57 views

Could a trajectory around a large mass ever deflect by more than 180 degrees due to general relativistic effects?

Possible mechanisms that could be an answer to the question What natural mechanisms could lead to the unlikely case of the same rogue asteroid or planet passing through our solar system twice? include ...
3
votes
0answers
24 views

Torque contacts

I experienced yesterday that when the slotted screw driver head was exact fit to the slotted screw, it was easier to turn the screw. I'd like to understand the physics of it. Is the bottom easier to ...
0
votes
0answers
20 views

How does the momentum conservation law hold for gravitational interactions in special relativity with Newton's third law being invalid?

Griffiths' argument that Newton's third law is invalid in special relativity The selected answer to the post above talked about momentum conservation in electrodynamics – Newton's third law ...
8
votes
2answers
589 views

Probabilities in non-stationary states

I'm confusing myself. Let's represent some state in the eigenbasis for Hydrogen: $$|\psi\rangle = \sum_{n,l,m}|n,l,m\rangle\langle n,l,m|\psi\rangle.$$ Now denote the initial state by $\psi(t=0)\...
1
vote
1answer
35 views

Counterterms in quantum brownian motion

In the part "Quantum Brownian motion" of the book, The theroy of open quantum systems written by Breuer, the author investigates on the Caldeira-Leggett model: The Hamiltonian of the particle is $H_{...
1
vote
3answers
90 views

Why doesn't a force perpendicular to the direction of motion change the speed?

It changes direction but not speed and this is proved in experiments. But is there any more "deep" reason as that space has isotropy and energy must be conserved per example?
0
votes
1answer
21 views

How to simulate plane Poiseuille flow using Molecular Dynamics? [on hold]

I want to simulate 2D plane Poiseuille flow using molecular dynamics (velocity verlet algorithm) but not able to understand exactly to how to do this. Boundary condition is fine, I am confused about ...
0
votes
1answer
17 views

How to perform an isothermal reversible expansion?

Take the case of an isothermal reversible expansion of a piston to lift a weight. As the piston expands, the temperature remains constant, but the volume increases. This volume increase implies a ...
-3
votes
0answers
20 views

How to find Kinetic energy of the block of mass M?Please provide a detailed solution [on hold]

(https://i.stack.imgur.com/FcsvD.jpg)(https://i.stack.imgur.com/W0BE0.jpg) The spring of force constant k2 just touches the wall and is not attached to the wall.The natural lengths of the strings are ...
-6
votes
0answers
53 views

Is there any reliable place where i can put my theory of universe (it explained/predicted the behavior of almost everything i came across) [on hold]

Is there any reliable place where i can put my theory of universe (it explained/predicted the behavior of almost everything i came across), so that people can ask question and i can try and explain ...
0
votes
0answers
10 views

Gauge fixing in Ginzburg-Landau simulation

I am developing a computer simulation of the Ginzburg-Landau model of superconductivity. In a few words, I have discretized the domain with finite differences and I am using Nonlinear Conjugate ...

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