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12 views

Manner of energy exchange between an accelerating charge and the velocity and acceleration fields it produce

The fields produced by a charged particle in accelerated motion produces an electric and magnetic field given by $${\vec E}(\vec r,t)=\frac{q}{4\pi\varepsilon_0}\left[\frac{(\hat{n}-{\vec \beta})}{\...
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1answer
37 views

Why does the answer here use $dS=Q/T$ even though this isn’t reversible?

This question for my thermo course ends up using $dS = Q_{\text{waste}} / T,$ but I was taught that $dS=Q/T$ is only valid if the process is reversible. The question makes it pretty clear it isn’t ...
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0answers
4 views

Is the buoyant force of air implicitly neglected for an object half-inmersed in water?

I saw in this answer that the atmospheric pressure is conveniently canceled mathematically when taking the atmospheric pressure at the level of the top of the object. However, when I was inventing ...
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2answers
53 views

Thought experiment : Does “ artificial gravity ” created in a spinning spaceship last forever?

We know, a body in uniform linear motion will continue to move with uniform velocity unless any external force acts on it. Similarly, a body rotating with uniform angular velocity will continue to ...
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0answers
11 views

Calculating heat transfer through a material when input temp, $K$ value and ambient temp known?

Ive got a chimney flue which will have heat up to 200c. The chimney flue will be wrapped in insulation with the thermal properties as per the screenshot of the table below. The ambient temperature of ...
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0answers
7 views

What is the best length ratio between 'tongue' element of the brick and brick wideness shown on this picture?

What is the best length ratio of 'tongue' element of the brick to brick wideness shown on the picture to resist an ertquake stres? Should the ratio be less than 1:2 as the tongue should feel higher ...
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0answers
33 views

How can I obtain the equation of state (EOS) of dense neutron star matter?

I am recently studying the equations of state of the neutron star. In the following paper,there are some tables and figs about energy density and pressure (I have attached tables 3 and fig 1 of the ...
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0answers
4 views

Pure rolling motion and different poles

Good evening dear forum users. My question concerns a highly rated topic in university physics courses: pure rolling motion. In particular, I would like to better understand the logic with which the ...
1
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1answer
416 views

Definition of creation and annihilation operators

An appropriately symmetrized (and normalized) $N$-particle physical ket can be expressed in the form: $$| \beta_{1}, \beta_{2}, \dots, \beta_{N} \rangle \equiv \frac{1}{\sqrt{N! \prod_{i=1}^{\infty}(...
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5answers
476 views

Acceleration in general relativity

Let's say that, from my point of view, another observer is accelerating. Now, from his point of view, he is standing still: all he feels is an overall fictitious force of gravity, which is just a ...
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1answer
47 views

Why does an electron or proton posses the property of a charge?

If seen, every property is caused due to some reason (eg: solids are hard due to strong force of attraction between its constituents particles), similarly what causes an electron or proton to posses ...
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0answers
44 views

Vacuum Energy in QFT under the Light of Divergence Invariance of the Lagrangian

The divergence invariance of the Lagrangian has been exploited many times, eg., for the purposes of obtaining a symmetric energy-momentum tensor --Belinfante-like-- consistent with GR. We know the ...
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0answers
35 views

Indistinguishability in statistical mechanics

I have two questions about using the concept of indistinguishability to determine the partition function in statistical mechanics, like for instance when determining the partition function of an ideal ...
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0answers
19 views

Gauge invariance prohibits the existence of other universes?

I'm only a student, so most likely misunderstood. The Wikipedia article on Relational quantum mechanics says: "The universe is the sum total of everything in existence with any possibility of ...
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1answer
19 views

Is the speed of an air bubble in a fluid equal to the fluid's speed?

The liquid (water) in a closed pipe system is pumped around. There are some air bubbles in the system. Do the air bubbles travel with the same speed as the fluid in the pipes?
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1answer
81 views
+50

Entropy and the brain

Maximum entropy is equivalent to minimum information in statistical mechanics and quantum mechanics and the universe as a whole is tending towards an equilibrium of minimum information/maximum entropy....
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1answer
282 views

Retarded time and corresponding position

EDIT: Added Clarification. By various methods, it's possible to determine that in the formula for Electric potential for the position of a charge in uniform motion, $V=\frac{q}{4\pi\epsilon_0\kappa \...
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1answer
42 views

What is “Fourier Transformation induced Spectroscopy” really? [closed]

With regard to "Conventional and Advanced Characterization techniques", what is meant by, "Fourier Transformation Induced Spectroscopy "? A detailed answer to this is most welcome. ...
11
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4answers
2k views

Why can no observer measure proper time here?

This is a relatively difficult question I found on a past exam (12% got it right): Two spacecraft travel in opposite directions, with spacecraft Ajax travelling at a speed of 0.5c and spacecraft ...
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0answers
17 views

Integral to obtain the current $I$ from the surface current density $\mathbf{K}$, Griffiths' Intro to Electrodynamics

I am reading the 4th Edition of Griffiths' "Introduction to Electrodynamics". It is not clear to me how to obtain the current $I$ from the surface current density $\mathbf{K}$. Griffiths ...
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1answer
174 views

Time-domain NMR or: When is the Fourier-Transformation not appropriate?

My question has two parts: One is general and has to do with the Fourier-Transformation, one has to do with Time-Domain NMR. Both parts are interlinked, of course. I tried to find out, why people do ...
5
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1answer
957 views

Do a floor tile or dry sand conduct electricity?

If you touch an electric wire while standing on a ground made of soil or floor tile, you will get electrocuted. So, electricity passes through it. Right? Shall I conduct an experiment by passing ...
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1answer
148 views

Doubt regarding proof of $pV = nRT$ [closed]

In my textbook, the proof for this formula is as follows: $$F \propto \text{Area}_{\text{wall}} \cdot \text{(number of density of particles I.e here m is const) I.e} \frac{n}{V} *\text{Average ...
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0answers
32 views

How can I get an unitary operator acting on the composed system from an unitary operator that acts on a subspace of the composed system?

In $S[42]$ in the supplemental material of this paper Vacancy-like dressed states in topological waveguide QED, the author wanted to construct an unitary operator $\widetilde{U}_S$ from another ...
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0answers
7 views

What is the name for the instrument to measure radiation consisting mainly out of a glass ball?

I remember vaguely a measurement instrument to protocol probably solar irradiance. The instrument mainly consisted out of a glass sphere and if I recall correctly, the sun was "writing" ...
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0answers
14 views

A problem on electrostatics and equilibrium of rigid bodies [closed]

Could someone help me solve this problem , I tried writing torque equations about an axis of rotation passing through any vertex of triangle and the centroid (centre of electrostatic force of ...
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0answers
14 views

Electricity IB Question [closed]

Where can the electric field be zero? a) position I b) position II c) position III d) positions I,II, and III. I'm really unsure about this question, and honestly don't know where to start.
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0answers
15 views

Please answer the following question [closed]

[![the given images contain the question][1]][1] The question is of statistical physics.we have to find the energy of system and possibility of finding system in state of negative absolute temperature
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0answers
39 views

Relative acceleration of fermions?

Let's say I want to know the relative acceleration between $2$ particles in quantum mechanics which obey the Hamiltonian $\hat H$: $$ \hat H = \frac{\hat p_1^2}{2m} +\frac{\hat p_2^2}{2m} + \hat V(...
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0answers
14 views

Lagrangian of a rotating disc with mass attached:

I have a slight question about finding the Lagrangian of a rotating disc of mass $M$ of radius $2R$ with a mass $m$ attached to a point on the rim. The disk is placed on its rim on a flat surface and ...
2
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4answers
48 views

Conceptual half-life Question

So I have this word problem and I’m a bit confused about it. I have the answer and explanation but I still don’t understand: The half-life of carbon-14 is approximately 5730 years, while the half-life ...
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0answers
7 views

Phase difference between electric and magnetic fields of EM wave in a conductor?

When an EM wave travels incide a conductor , we see that there is a phase difference between the Electric and magnetic fields within the conductor. The magnetic field lags behind the E field and this ...
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0answers
11 views

Soliton solutions of dispersionless systems

I am working on soliton theory. As a well known definition of soliton is that is appears due to a balance between nonlinearity and dispersion effect. I am not getting any satisfactory answer why ...
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1answer
51 views

Is $\mu$ the renormalization or factorization scale in the DGLAP equations?

The DGLAP equations read $$\frac{\partial f_i(x,\mu^2)}{\partial\ln\mu^2}=\sum_j\int^1_x\frac{dz}{z}P_{ij}(z,\alpha_s(\mu^2))f_j\left(\frac{x}{z},\mu^2\right),$$ where the $f_i$ are the parton ...
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3answers
51 views

When do I use the cosine and sine functions when graphing the components of a vector?

I have a vector $F_e$ and I would like to graph it to its corresponding $X$ and $Y$ components. I know that the $i_y$ component is negative, and there is no $i_x$ component. $\vec{F_e} = F_x\vec{i_x} +...
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1answer
83 views

What is the work done by friction on a body which is rolling with slipping?

A hollow sphere is released from the top of an inclined plane of inclination $\theta$. (a) What should be the minimum coefficient of friction between the sphere and the plane to prevent sliding? (b) ...
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0answers
25 views

Moment of inertia of cylinder drilled with conical hole

I want to find the moment of inertia of the following solid: Cylinder drilled with a conical hole. It is given that density is constant $\rho_0$. So, what I did: $${I_z} = {\rho_0}\int\limits_U {\...
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0answers
22 views

Invariance of spin-polarized Kohn-Sham Hamiltonian with respect to spin rotations

In collinear density functional theory, Kohn-Sham equation for spin-dependent wave functions is $$ \left[\left(-\frac{\hbar^{2}}{2 m} \nabla^{2}+\int \frac{n\left(\mathbf{r}^{\prime}\right)}{\left|\...
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0answers
4 views

Axis to take when finding time period of oscillation after perturbing a dipole in an external electric field

Suppose I have sum of forces is zero, this means that torque is independent of the origin I take the torques around, but then there is a problem here, the inertia about any particular point is ...
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4answers
284 views
+50

Free-body diagram of a rack of blocks revisited a.k.a. if it were on top of lava, which block would you choose to stand on?

This question is a follow up to the following question asked by esdoublelef Free body diagram on a rack of wooden blocks To repeat, consider a rack of blocks (each block is a cube), that are held up ...
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1answer
103 views

Ising model: How is $|\langle\sigma\rangle|^{2}=\lim _{r \rightarrow \infty} G^{(2)}(r)$?

In the book of Statistical Field Theory by Giuseppe Mussardo, on page 51, it is given while talking about Ising model that One arrives to the same conclusion by analysing the possibility of a non-...
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1answer
15 views

Current flowing in a circuit made up of ideal conducting wires

Taking a simple circuit with a battery to provide a potential difference and some resistance across, also our circuit is made up of an ideal conducting material so $\sigma$ is infinity. Now I have ...
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0answers
9 views

What are the basic principles of experimental electromagnetism? [closed]

I want to learn about experimental physics in the context of electrodynamics and electrostatics. Basically I'd like to know how we are able to measure different quantities in this field (electric ...
5
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6answers
692 views

Can acceleration depend linearly on velocity?

Is it possible that acceleration may vary linearly with velocity. Is it practically possible, if so is there a practical example of it? By integration I was able to verify that for the above case to ...
2
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1answer
55 views

A Doubt on Hawking Radiation: What Birrell wants to say here?

Well, I know basic General Relativity but I still learning the basics of Quantum Field Theory (therefore without mentions on curved spacetimes). But, I'm trying once and a while to become more used to ...
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2answers
27 views

Gravitational potential energy in a system of two particles

if we have $m_1$ and $m_2$ as two particles separated by a distance $r$, then gravitational potential energy of this system is $-Gm1m2/r $. why do we not add their gravitational potential energies ...
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0answers
4 views

DPDT relay and H-bridge [closed]

I am trying to make a circuit so I can use an arduino to change the rotation of a dc motor , so I am thinking about using an H-bridge made of a DPDT relay connected to the arduino. Would it work? Also ...
8
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6answers
532 views

How to find the falling time of an object when acceleration is not a constant? [closed]

Let's say we are throwing an object from the surface of the earth, this object reaches 70,000km with initial velocity of $10713 \mathrm{m}/\mathrm{s}$ until it reaches the peak high , the g value at ...
2
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1answer
401 views

What is the refractive index for partially ionized plasma (mixture of electrons, ions and atoms)?

I asked a question earlier, why ions are not included in the refractive index of plasma . What I do not understand is how a refractive index of plasma can be formed mathematically for plasma that is ...
12
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3answers
198 views

To what extent can one recover plane waves from the Airy eigenfunctions of a linear potential as the field is turned off?

Consider a single massive particle in one dimension under the action of a static linear potential, with the hamiltonian $$ \hat H=\frac{\hat p^2}{2}+\hat{x}F_0. $$ The eigenstate at energy $E$ is, ...

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