0
votes
0answers
33 views

Change without Work

Is it possible for the state of the universe to change without any work at all being done? Or, more specifically, is it possible for some physical change to occur without work being done? (Note that ...
0
votes
1answer
34 views

Is displacement in circular motion a chord or an arc?

When taking the displacement between two points along a circular path to calculate its velocity, do you take the length of a chord connecting the two points or do you take the length of the arc ...
0
votes
2answers
34 views

A car honking it's horn, how long until the car hears the sound reflected? [on hold]

A car is traveling with a constant speed v on a straight road which forms an angle α with nearby straight wall. When the car is at a distance l from the wall the driver presses the horn briefly. What ...
0
votes
0answers
9 views

Range of thermocouples

Why do thermocouples have a restricted range of temperature that can measure, say for example some go from –200 °C to +268 °C, what makes them to be useless below or above?, I know above may become ...
0
votes
0answers
25 views

Angular Speed and Normal Speed

The instantaneous speed of a point along a circular path is given by $v=\omega r$, where $\omega = \frac{\Delta \theta}{\Delta t}$, $s=\Delta \theta r$, and $v=\frac{s}{t}$. However, isn’t the ...
0
votes
1answer
20 views

Why is there longitudinal conductance in a partially-filled Landau level?

Suppose I consider an infinite, non-interacting (so no FQHE should happen) 2DEG in the magnetic field $\vec B=B\hat z$ with a non-integer filling factor, say 0.13 or whatever. Suppose I apply an ...
0
votes
1answer
23 views

Why does surface tension of water-ethanol binary mixture decrease with increasing concentration of ethanol?

I was thinking that it must be due to weaker hydrogen bonding in ethanol than in water. But then I learnt that Raman Spectroscopy and viscosity measurements suggest that upto a certain ethanol ...
0
votes
0answers
14 views

How do you calculate the electric tension between two charged entities?

If: 1) you know the coordinates and individual charge(in coulombs) of each object and 2) voltage is the difference in electric potential energy between two nodes How do you calculate the voltage in ...
0
votes
1answer
15 views

longitudinal magnification confusion in concave mirror

If you move a rod lying on the principal axis of any concave mirror, when the near end of the rod is at a distance equal to half it's own length from the mirror, then the instantaneous velocity of ...
0
votes
0answers
19 views

Centripetal Force Doubt

I have'nt understood the solution that has been provided: Question: Solution : I did'nt understand the part where they stated that for the water to not fall out of the bucket, N>= 0 I'm a high ...
0
votes
0answers
16 views

The induced electric field of an infinite current carrying wire

I am given, without motivation, that the induced electric field from an infinite, straight, current carrying wire is parallel to the wire itself. $$ \vec{I} \times \vec{E}_{\text{induced}} = ...
0
votes
1answer
35 views

Help with proving a relation

I am trying to see if the following relation, \begin{equation} \frac 12 g_{ij}\frac{d^2\eta}{du^2}+\frac 12 g_{ij}\frac{d\eta }{du}+\frac 12 \frac{\partial g_{ij}}{\partial x^j}\frac ...
0
votes
0answers
22 views

How is ampere defined for alternating current?

Both alternating current and direct current are measured in ampere. But how is ampere defined for alternating current? It cannot be defined from two mutual attraction of two parallel wires carrying ac ...
0
votes
0answers
8 views

Regarding IMU derivation of position/orientation

If you are familiar with IMUs (Inertial Measurement Unit) , you know that before the double integration to arrive at estimating the position, one has to subtract the gravity from the measured ...
0
votes
0answers
13 views

How do you calculate minimum speed for a mass to move vertically in a circle [on hold]

For part c) would you subtract the top and bottom tensions to find the minimum velocity. The answer should =2.7 m/s for part c).
0
votes
1answer
22 views

Light Spectrum - Sum of Waves or Collection of Waves

I'm wondering about the spectrum of light that is often shown pictorially as a distribution of power, say, from sunlight. My question is: does this indicate that each wave of light contains all of ...
0
votes
0answers
16 views

Laser Energy Level Transitions

I am new to Laser Physics. While looking at the Energy Levels diagram for the Laser Transition of ND:YAG laser, I see energy levels labeled like 4F(3/2), 4I(15/2),.. I did not come across such energy ...
0
votes
0answers
24 views

entropy balance equation in thermodynamics [on hold]

can any body help me to prove the following entropy balance equation. \begin{equation} T \frac{ds}{dt}=- div \mathbf{q} \end{equation} where $T$ is absolute temperature and $s$ is entropy $\mathbf{q}$ ...
0
votes
1answer
32 views

Fourier expansion and transform - what about the phase of the waves that i am adding?

Say we have a wave on the surface of the water and we want to describe it as a sum of other waves. So we use Fourier expansion to add waves of different wavelengths. For simplicity, say we have to ...
0
votes
0answers
20 views

What came before the Big Bang? [duplicate]

Is it an inflating bubble in a space time foam? Some concluded that "whereof one cannot speak, thereof one must be silent"
0
votes
0answers
3 views

Water flow in salt solutions contemporary exposed to an electrical and constant magnetic field

When a permanent magnet is held motionless close to a salt solution which already has been exposed to an electrical field a flow in the water will be induced and can be detected by applying some ...
0
votes
0answers
14 views

Slope field of y'=x^2 - y^2 [migrated]

I don't know how I am supposed to go about creating a table with slope values for the graph so that I can sketch them. I knew how to do it when y' equations had y only or x only, but not when both are ...
0
votes
0answers
6 views

Diamagnetic Sphere Moving through Solenoid

I've seen the videos of frogs being levitated due to diamagnetism. What happens if the frog (or another diamagnetic object) enters a solenoid with an initial velocity? Specifically, consider a ...
0
votes
0answers
9 views

Can QKD nodes use a constantly evolving key?

In QKD we know that we can generate random secret keys using quantum entangled photons, measuring their qubits and then using noise reduction to negotiate probably similar bits between Alice and Bob. ...
0
votes
1answer
25 views

Good values for gravitational potential [on hold]

In the context of a project, I had to solve numerically Poisson equation with cylindrical coordinates. I put here results for z = 0 on a 3D mesh 256x256x256. Below 1 figure representing the final ...
0
votes
0answers
34 views

Can I Wick-contract terms with derivatives with terms without derivatives?

Consider for example the QCD three point vertex, can I contract a gluon field with the gluon field with a derivative in the vertex?
0
votes
1answer
46 views

Electric field inside two parallel lines of charge

At what force will a particle be subjected to inside two parallel line charges with the same length and charge density. I get that in the middle the forces will cancel, but will they cancel if the ...
0
votes
0answers
51 views

Can you have more than two entangled particles? [duplicate]

Given the diagram on the wikipedia page for Quantum Entanglement we a beam of photons hitting a crystal which splits the beam into to entangled particles. Is it possible to split the beam into four ...
0
votes
1answer
63 views

Do relativistic electrons have more charge?

Gauss's law tells us that the total electric flux out of a closed surface is equal to the charge enclosed divided by the permittivity. When a charged particle is moving close to the speed of light ...
0
votes
2answers
60 views

Does the frame of reference change the behavior of a particle

"Behavior" word in the title is not very correct. I'm in a train at a railway station and on the platform there is a glass case (the mass of case is 5 kg and if it gets hit with a velocity of 10 N ...
0
votes
1answer
42 views

Calculating output forces of bicycle wheels

Based on the force on the rear gear $F_t$ and the radii of the rear gear $R_g$ and rear wheel $R_w$ , how would you calculate the force the bicycle exerts on the ground when it is accelerating? I ...
0
votes
0answers
17 views

Using stellar spectroscopy to measure stellar parameters, why is it log g?

Stellar spectroscopy can in principle measure the stellar surface gravity, radii, effective temperature, and stellar rotation. Why is it that surface gravity g is ...
0
votes
0answers
24 views

Free fall and gravitational time dilation

An observer 'A' at rest in a gravitational field has some amount of time dilation relative to an observer 'B' far away from the gravitational field. Would the clock of an observer 'C' in free fall at ...
0
votes
1answer
25 views

Thermal expansion of metal spring

I am attempting to figure out why a laser layout tool I have is drifting over time. It was designed with a small adjustment mechanism that relies on a spring to apply pressure to a fulcrum that ...
0
votes
0answers
27 views

Difficulty in understanding Maxwell Boltzmann distribution in case on ions in a field

I learned that the velocity of molecules obey Maxwell Boltzmann (MB) distribution at a Temperature T. If I have ions of mass 'M' accelerated to 2eV in a specific region. As the ions are not ...
0
votes
0answers
30 views

change in free energy at natural state

I am styding a book on thermoelasticity, here free energy $f(e_{ij},T)$ is expended into taylor series in the vicinity of the natural state (when $e_{ij}=0$,$T=T_0$) and entropy s such that ...
0
votes
1answer
59 views

Children of entangled particles

Theres a photo on the wikipedia page Quantum Entanglement there's a image of a photon being split into two entangled photons via crystal. I used this picture to demonstrate the scenario below. ...
0
votes
0answers
4 views

redistribution of charge between plates

How is charge redistributed when a charged conducting plate is placed between two identical wire-connected uncharged plates?
0
votes
1answer
60 views

is there an operator which measures the mass of particles?

When I studied a spin, the textbook said spin is an intrinsic quantity like mass. However, while we can calculate just expectation values $ \langle \textrm{S}^2\rangle $ or $ \langle S_z\rangle $, the ...
0
votes
0answers
32 views

QED+Classical Background Renormalization

I would like to ask a question related to quantum corrections and renormalization in QED. We have the QED vertex $\overline{\psi}[-ie \gamma^{\mu}(B_{\mu}+A_{\mu})]\psi,$ being $B_{\mu}$ a classical ...
0
votes
0answers
19 views

Electric field radiation with moving charge and observation point

I've been working on Chapter 34 of the first volume of the Feynman Lectures on Physics http://www.feynmanlectures.caltech.edu/I_34.html#Ch34-S1. In Fig. 34–3 (reproduced above) Prof. Feynman shows ...
0
votes
1answer
28 views

How does rainbow stay for such long time even it is caused due to raindrops?

Rainbow forms when light rays pass through a raindrop (usually, it can be a watet droplet also) and it undergoes several phenomenon like refraction , reflection , dispersion , But after the rainbow is ...
0
votes
0answers
27 views

How M theory or String theory explains fundamental forces and Quantum mechanical phenomena? [on hold]

How M theory explains fundamental forces gravity,strong,weak and electromagnetic? And how does M theory explains phenomena of light like reflection,refraction,diffraction,interference etc?
0
votes
0answers
12 views

Question related to charged concentric conducting shells

There is a charged conducting spherical shell given a certain positive charge.Another larger spherical shell is given the same negative charge.The first shell is now placed inside the second shell so ...
0
votes
0answers
44 views

Why should physical theories always have a Lagrangian formalism? [duplicate]

I've often heard that every physical theory has some kind of Lagrangian formalism, or a formalism in terms of a principle of stationary action. The Standard Model has one, General Relativity has one, ...
0
votes
0answers
61 views

Klein-Gordon Field Angular Momentum Operator in Terms of Creation and Annihilation Operators

I am computing the angular momentum operator for real Klein-Gordon field (essentially question six of here (though please note this is not a homework question, I am following through Tong's course via ...
0
votes
1answer
29 views

How to produce a given entangled state of two quantum bits?

I was watching Leonard Susskind's video series on quantum entanglement, where he looks at the spins of two electrons. In particular, there are entangled states of the form $$\alpha\left|\uparrow ...
0
votes
0answers
16 views

If we considered chiral perturbation theory with coplex $\phi$-s, wold the next lo leading order renormalization $\gamma$-s change?

The Lagrangian of chiral perturbation theory (with two quark flavors) is written using the following matrix $U$ $$U=e^{i\sigma^i\phi_i/f}$$ where $\sigma^i$ are the Pauli matrices, $\phi_i$ are three ...
0
votes
1answer
15 views

How to get a better handle on Spectral Irradiance conversion?

I'm using a computer program to simulate a lightsource. I can feed my own spectral irradiance values into the program to simulate color rendering accuracy. The program takes values in electron volt ...
0
votes
1answer
27 views

RF disturbances produced by transmission power lines

I need a book or paper that contains "the effects of transmission lines on the radio frequency transmission and disturbances". Could you help me find a useful textbook? Thank you

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