0
votes
1answer
23 views

Period of small oscillations of rotational disk [on hold]

This is a question on a university physics exam paper, and it doesn't seem immediately intuitive how the problem works. The answer is given, but not any details of the working. Also, I'm not sure if ...
1
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0answers
20 views

What happens to the emf generated due to a change in magnetic flux in a coil?

When we move a magnet into a coil of wire (open circuit) and then out of it, we create a emf across the ends of the coil and another emf in the opposite direction. My question is what would happen to ...
1
vote
4answers
86 views

Gravitational force of a ring [on hold]

Given a ring with mass $m_1$, radius $R$ and a point mass $m_2$ with distance $x$ regarding the center of the ring. How can I calculate the gravitational force of this ring ? At first glance I'd say ...
0
votes
0answers
18 views

Timescales for isothermal processes

My understanding is that processes in ideal gases need to take place over relatively long timescales to be idealised as "isothermal" such that the gas temperature can be assumed not to change. For ...
0
votes
0answers
13 views

Planck's law versions: intensity vs energy density vs spectral radiance

Here it shows there are three (considering only the wavelenght or frequency cases) ways of writing Planck's law. I am trying to derive them from one another. I converted from spectral radiance ...
0
votes
0answers
30 views

Photons under pressure

Does it make sense for photons to be put under pressure, if so how would this be measured? I'm wondering because I would like to plug in $E = h\nu$ into the formula for enthalpy.
1
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0answers
32 views

Which technique is used to measure huge astronomical distances which are in terms of billions of light years? [duplicate]

I know what a "light year" means. However, I am very curious to know about the technique through which scientists are able to calculate the distance of various astronomical bodies from earth which are ...
0
votes
0answers
21 views

A circuit with a solenoid and no resistors

We have an electric circuit consisting only of a solenoid (its two ends are connected). Let's suppose that the total length of wire used is $l$ and the wire has a cross-section of area $S$ and ...
-2
votes
0answers
44 views

Special relativity revisited [on hold]

I had a query about Einstein's special relativity, particularly when it came to the notion of $c$ being the ultimate speed. I resolved such a query by treating an imaginary particle traveling at an ...
0
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0answers
13 views

Why must the deviations from equilibrium be small for zero difference in energy in this solenoid?

A long solenoid with a square cross-section is partially immersed in a magnetic, non-conductive liquid of permeability $\mu$. The solenoid's axis is parallel to the liquid's surface. ...
-1
votes
0answers
27 views

Derivation of Maxwell's equations [on hold]

I derived the equations of Maxwell in a current free medium, last year about this time (I need help editing this). I made use of complex quantities, and Cauchy-Riemann relations. In this derivation ...
2
votes
0answers
25 views

How come a current sheet of $J_s = J_0 \hat{x}$ produces plane wave solution?

Given in the picture. There is a current sheet $J_s = J_0 \hat{x}$. Supposedly Jo is not oscillating. So, how does this thing create a plane waves propagating away from the current sheet? Shouldn't ...
0
votes
1answer
43 views

Where does mass go when energy is converted in to photons?

If matter and anti-matter annihilate each other they emit a photon with the energy that corresponds to the mass, right? This is the best example I could think of matter/energy being converted directly ...
1
vote
1answer
54 views

Geometry of Hamilton-Jacobi Equation

I'm trying to understand the geometry of the Hamilton-Jacobi equation (working from Gelfand + Fomin), but I'm stuck. I know that: If we define the function $S(t,y;t_0, y_0)$ as: $$S(t,y;t_0,y_0) = ...
0
votes
0answers
19 views

How can i convert an audio into a waveframe? [on hold]

I'm interested in finding out how to convert a conversation, from it's audio form in a graphic script, audiowaves Thank you and have a blossom day!
1
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0answers
62 views

How to understand singularities in physics?

The question is probably two-folded and I will try not to make it too vague, but nonetheless the question remains general. First fold: In most physical laws, that we have analytic mathematical ...
1
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1answer
41 views

Redshift of supernova light curve

I am trying to understand how the width of a supernova light curve depends on the redshift of its component frequencies. Let us make the simple assumption that the light curve is Gaussian. The ...
3
votes
1answer
29 views

Air nozzle outlet profile efficiency, concave/convex

I need to design a contracting nozzle for air. The application is quite simple, consider it like an hair dryer but the flow speed is even lower. So the Mach number is very low and the flow laminar. If ...
1
vote
1answer
46 views

Units consistency

Does $^\circ\mathrm{C}^2$ have any physical consistency? I know that $\mathrm{K}^2$ is a valid units even if I don't know in which context it can be used. But I feel strange about $^\circ\mathrm{C}^2$ ...
0
votes
0answers
9 views

What is a re-entrant energy contour in a band structure?

I have a question involving band structure in solids. What does it mean to say that an energy contour in a band structure is re-entrant? Herbert Kromer uses this term in: H. Kromer, Phys. Rev. 109, ...
0
votes
1answer
16 views

Alpha particle in vacuum

Does the alpha particle travel in vacuum for ever and ever or can it undergo some transformation eg two protons get separated or the neutron decays etc.?
0
votes
1answer
32 views

Propagation of uncertainty - which formula? [duplicate]

Can someone explain to me when do I use this formula ...and when do I use this one?
0
votes
1answer
29 views

CMB anisotropy, temperature and doppler effect

How would you derive the following equation: $$ T' = T_{CMB} \left( \frac{\sqrt{1-v^2}}{1+v\cos{\theta}} \right) $$ which describes how the temperature of the CMB varies due to the speed $v$ of the ...
0
votes
0answers
15 views

Diffeomorphism invariant of renormalized operator insertions in curved worldsheet

In Polchinski's String Theory vol 1, eq 3.6.5, it is stated that the renormalized operator insertions in curved worldsheet (basically, the generalization of normal ordering in flat worldsheet) is ...
0
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0answers
45 views

1 + 2 + 3 … = -1/12 appears in bosonic string theory. Is this regularization method also used in superstring theories?

I found two previous posts on this, but no specific answer to my question. How does the sum of the series “1 + 2 + 3 + 4 + 5 + 6…” to infinity = “-1/12”? What areas of physics depend on the sum $1 + ...
0
votes
1answer
29 views

1D Ising model and degenerate states

I am studying the Ising model in 1D, in the absence of magnetic interaction but in presence of an external magnetic field. The Hamiltonian for an Ising chain with $n$ sites is hence described by $$H = ...
0
votes
0answers
12 views

Relativistic doppler effect in three dimensions

Consider a sphere that travels through space with a velocity $v$. I wish to investigate the relative intensities of the CMB on all points on the sphere. For the microwaves approaching from the direct ...
3
votes
1answer
47 views

Why does this proof show the gluon propagator comes from the first two terms?

I am reading the book "QCD: Renormalization for the Practitioner" and i am having trouble understanding something. In page 70 the gluon propagator is written as follows $$\begin{multline} ...
19
votes
4answers
4k views

Could I break the sound barrier using circular motion? (And potentially create a sonic boom?)

Ok, Lets say I get out my household vaccum cleaner, the typical RPM for a dyson vaccum cleaner reachers 104K RPM, Or 1.733K RPS. In theory, this disc would be travelling with a time period of ...
3
votes
2answers
75 views

How to count the number of modes/polarizations of a Gaussian field theory?

A Gaussian (free) field theory is described by a quadratic action of the field, e.g. $S=\int\psi^\dagger K\psi$ (or $S=\frac{1}{2}\int\phi^\intercal K\phi$ for real fields). Usually one just need to ...
0
votes
2answers
81 views

Help with high school physics [duplicate]

I am studying high school physics and it seems i have memorize the equation and use it mechanically in doing question and memorize lots of physical phenomena.I know a lot of physical phenomena can be ...
-1
votes
0answers
14 views

How much is the gain of this Op Amp? [migrated]

I have a circuit like this. I want to calculate the gain of this circuit. If there is no R4 then it is easy to calculate.But now I have a problem. If I have a input current I=0.5A, then what is the ...
1
vote
1answer
22 views

Energy for burning things!

I have a cylindrical lens & a surface that can be burned.( for example wood , sheet ,...) In a sunny day , I wanna burn the surface but I don't know the "Energy for burning surfaces" If the ...
1
vote
1answer
36 views

How to calculate the Hamiltonian from the Lagrangian for a non-relativistic charged point particle in an EM field?

I was given the equation of the Lagrangian: \begin{equation} L~=~\frac{1}{2}m \dot{x}^2+\frac{e}{c}\vec{\dot{x}}\cdot \vec{A}(\vec{x},t)-e\phi (\vec{x},t). \end{equation} I proceeded to use the ...
0
votes
1answer
57 views

What exactly is quantum spin? [duplicate]

What is "spin" as it relates to subatomic particles? I've heard that it's similar to angular momentum but I've also heard that's not completely the case.
0
votes
0answers
26 views

Landau theory of phase transation

In his article http://www.ujp.bitp.kiev.ua/files/journals/53/si/53SI08p.pdf, Landau defines probability distribution $\rho$ which is related to symmetry of crystal. If crystal has certain symmetry ...
0
votes
0answers
25 views

How to calculate liquid pressure regardless of the gravity?

Assume we have a balloon in a tank filled with a liquid , without any gravitational forces: We just know the Temperature, V0 and V1 I want to calculate the pressure exerted from the liquid on the ...
1
vote
1answer
37 views

Work done in raising a rope at constant kinetic energy?

Usually the question I had was work done in raising a rope at constant speed. Obviously as you raise the rope, the mass changes over time. It'll be a simple integral. But what about work done in ...
-1
votes
0answers
22 views

Do all the emitted electron in photoelectric effect have same K.E [duplicate]

we calculate Max K.E of emitted electron.why max?
1
vote
2answers
130 views

Is the Wikipedia version of the Heisenberg equation of motion correct?

Back in 2011, this question asked about the Wikipedia version of the Heisenberg equation of motion for an operator $A$: \begin{equation*} \frac{d}{dt} A(t) = \frac{i}{\hbar} \left[ A(t) ,H \right] + ...
0
votes
3answers
54 views

Why is the total energy of an orbiting system negative?

Assume it's an circular orbit. Object A orbits around object B. Take object B as frame of reference. .$E=KE_a + GPE$ .$E=\frac 12m_av_a^2 +(-\frac {GM_bm_A}r)$ .$E=\frac 12m_a(GM_br)+(-\frac ...
0
votes
2answers
27 views

When I change the rpm of a turntable, how long does the turntable to get to the new rpm?

If the turntable was rotating at 16 rpm and I switched it to 30 rpm, is the change in speed pretty much instantaneous, or is their a period of acceleration? When I did it, the change appeared to be ...
1
vote
0answers
26 views

How does non-constant conductivity change surface charge on a wire?

Current density is equal to conductivity times electric field. Therefore flux through a cross section of a wire is equal to current over conductivity. Current has to be constant along a wire. This ...
2
votes
0answers
32 views

Where can I find a table for NIST standards on temperature and pressure?

The Wikipedia article Standard conditions for temperature and pressure notes that IUPAC and NIST are two of the most common standards for temperature and pressure in use. Even if I could have gotten ...
0
votes
1answer
57 views

Earth's direction in space

After watching videos about the rotation of the planets being helical and not heliocentric, I wondered, as Earth travels through space, which part of Earth is the forefront?
1
vote
2answers
64 views

Spin in magnetic field and eigenvalues

We have some arbitrary quantum state, lets say $$\vert\Psi\rangle=\alpha_{1}\vert\uparrow\rangle+\alpha_{2}\vert\downarrow\rangle= \begin{pmatrix} \alpha_{1} \\ \alpha_{2} \\ \end{pmatrix}$$. And ...
0
votes
1answer
39 views

Smallest Black hole nessesary to devour Earth?

While looking into black holes I can across the idea of hawking radiation, and the fact that microscopic black holes would near instantaneously evaporate before doing any damage. However larger black ...
2
votes
1answer
54 views

effective field theory of the projective semion model

The "projective semion" model was considered in http://arxiv.org/abs/1403.6491 (page 2). It is a symmetry enriched topological (SET) phase. There is one non-trivial anyon, a semion $s$ which induces a ...
5
votes
1answer
40 views

What's the next big goal of the Large Hadron Collider?

Obviously, physics lovers everywhere were excited at the announcement that the LHC had verified the existence of the Higgs Boson. As a non-physicist, I like to keep up with what I can regarding the ...
1
vote
1answer
54 views

How to motivate this approach on Special Relativity?

One of the most common approaches to Special Relativity is that based on the two Einstein's postulates: The laws of Physics are invariant in every inertial reference frame The speed of light ...

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