Questions tagged [energy]

Energy is the conserved quantity associated to time-translation invariance and represents the work a system is capable of doing. Use this tag for questions about energy, and consider adding [tag:energy-conservation] if it is specifically about its conservation.

584 questions with no upvoted or accepted answers
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9
votes
2answers
640 views

The ADM energy of gravitational waves?

I have been looking for books about this question for several days. However, almost all books use Landau–Lifshitz pseudotensor to calculate the energy of gravitational waves. And they said the result ...
8
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2answers
169 views

Why is my solar panel more efficient as the temperature increases, rather than less efficient?

I have recently performed an experiment in which I placed a solar panel inside a closed box, together with a heater and a lamp (60W). I increased the temperature using a heater from 20ºC to 50ºC. The ...
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322 views

Could energy be stored into (not extracted from) the quantum zero point field (like a battery)?

In order to explain the question clearly, I will make a short introduction. In 1962, Josephson predicted that for a sufficiently thin insulating layer, it should be possible for Cooper pairs to ...
7
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1answer
185 views

Why alpha particles inestead of hydrogen or duetereum?

I know atoms undergoing alpha decay emit alpha particles, but I was wondering why specifically helium nuclei? If these atoms wanted to emit the smallest unit of matter (I'm talking about hadrons here, ...
6
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0answers
327 views

Free Energy Landscape - Construction and meaning?

I struggle to understand the concept of free-energy landscape. It seems to me the concept makes perfect sense for energies, but not for (canonical) free energies. In my actual, hopefully to be ...
5
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1answer
387 views

Sum of energy for 2 solids in rotation

I would like to compute the sum of energy of the following case: Two solids are turning (disks). Yellow solid is turning at $w_1$ radians per second around its center of gravity and blue solid is ...
5
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0answers
547 views

What is the link between free energy and lagrangian?

Free energy is a generalization of energy when the system exchanges heat with the environment. Energy, in its turn, can be extracted from lagrangian under the symmetry of time $(\frac{\partial L}{\...
5
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0answers
376 views

How efficient is the Crookes radiometer?

I remember many years ago, I think at 8th grade, seeing the teacher show us a Crookes radiometer. I remember it being very fascinating. Today I read the wiki article on it, after looking up what it ...
5
votes
1answer
81 views

How much energy is radiated when matter falls into a black hole

When a black hole consumes matter, it can form an accretion disc. Is there a relationship between the mass of the falling matter $m$, the mass of the black hole $M$, and the energy radiated during the ...
4
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2answers
152 views

Why the rubber ball bounced higher than the glass ball

For a teaching degree we did the following experiment: Drop a rubber and a glass ball of approx. same size from approx. same height onto laminate flooring. As we expected, the rubber ball bounced ...
4
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0answers
129 views

Why do electrons abide by Hund's rule?

Is the reason why Hund's rule exists, that when electrons are in different orbitals (such as 2px, 2py, or 2pz), they are most stable (lowest energy)? If the purpose is stability/lowest energy, ...
4
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2answers
251 views

Is energy $E$ in Schrödinger equation an observable/ Can $E$ be measured?

Take this quantum approach to estimate mean energy of a molecule: $$\langle\psi|H|\psi\rangle=\overline E$$ Question: Is $E$ an observable? How we can compare it to an experimental value? i.e how ...
4
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0answers
546 views

What is the third peak in the spectrum of Sodium-22?

I collected this spectrum from a sodium-22 sample in an instructional laboratory. The sample was set in front of a germanium detector which sends a signal into a pulse height analyzer and plots a ...
4
votes
1answer
476 views

Why the convexity of $E(S,V,N)$ implies that at thermodynamic equilibrium the energy is minimal?

I do understand that in the case of mechanics for example, if there is a soccer ball inside a "well", at mechanical equilibrium, the ball will be at the bottom of the well. ball http://electron6.phys....
4
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0answers
329 views

Energy of a particle as measured by an observer at infinity

I'm wondering if it is possible to make a definition for the energy of a particle as measured by an observer at infinity. I've looked through Wald for this but wasn't able to find anything - I may be ...
4
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1answer
163 views

Mutual capacitance upper limit

I am having trouble making an analog for mutual capacitance from mutual inductance. In circuits with magnetic coupling, there is an upper limit established on mutual inductance due to energy ...
4
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1answer
1k views

How to convert Richter magnitude scale to approximate TNT?

I know the Richter magnitude scale is often used for measuring the strength of earthquakes. At the same time, explosive/destructive releases of energy are often quoted in equivalent amounts of TNT. Is ...
3
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1answer
75 views

Significance of energy in a time dependent quantum box

The Hamiltonian for a particle in a finite box is $$H = \frac{p^2}{2m} + V(x)$$ which will give time evolution as $$ i\hbar d/dt|{\psi(t)}\rangle = H|{\psi(t)}\rangle \, .$$ However, if I do a ...
3
votes
1answer
79 views

Physical significance of free energy in canonical ensemble?

From macroscopic thermodynamics I understand that the free energy equals the total energy of the system minus the energy it would have cost a thermal reservoir to create it. So any energy in "excess" ...
3
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0answers
80 views

Integrated vs. Differential Form of the Enthalpy

I have been under the impression that the definition of enthalpy as $$H = U + PV$$ is purely mathematical, the result of taking the Legendre transform of the internal energy $U$, and merely provides ...
3
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0answers
106 views

Can the Taylor expansion of Energy/Intensity be explained more in-depth?

In reference to the question, "Why is energy in a wave proportional to amplitude?" Ben Crowell answered with the answer attached. The original post is linked here. I did not respond to the original ...
3
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1answer
100 views

Quantization of Klein-Gordon field between two boundaries

Consider a real scalar $\phi(x,t)$ with mass $m$ in $1+1$ dimensional spacetime, described by the 2d free Klein-Gordon action. $\phi(x,t)$ lives on an interval $0 \leq x \leq L$, and is subject to ...
3
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1answer
94 views

Shooting an electrically neutral ball vs. a charged ball

If we had two identical conductive spheres of masses $m$, one with $–q$ charge and one neutral, would it take the same amount of energy to accelerate each of them to a certain velocity $v$? Uncharged ...
3
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0answers
142 views

Constant work function although changing Fermi energy

I'm working with the following book “Interfacial Electrochemistry” (2nd Edition) written by Wolfgang Schmickler and Elizabeth Santos and I'm trying to understand the process described in section "...
3
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2answers
86 views

Does shortening the path length of an excited etalon do work? What about LIGO?

Start with a high-Q etalon excited on-resonance with a laser for a time long enough that it has built up an essentially stable standing wave. There is a constant outwards-directed force on each mirror,...
3
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3answers
660 views

Dissipation and first law of thermodynamics

Consider the following situation: a certain gas is contained in a well-insulated cylinder with a well-insulated piston head. Now, in this case the piston is not frictionless. In order for the piston ...
3
votes
2answers
43 views

How to efficiently cool down simulated gas by time-dependent potential?

I'm trying to simulate condensation of a highly diluted gas (a model gas, not any real one). For simplicity I restrict the simulation to 2 dimensions. To setup the simulation I take some interparticle ...
3
votes
1answer
556 views

Entropy: Disorder or energy dispersal?

The first definition of entropy given by Clausius is I believe this $$S=Q/T$$ It is as I understand a common fact to understand entropy and maybe often teach it as a measure of disorder through the ...
3
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0answers
164 views

What role did the Higgs boson play in the Big Bang?

Scientists say that inflation stopped when a very peculiar energy was mobilized, did Higgs boson play any role in this? What is it's relation to the Big Bang? Some physicists, such as Michio Kaku, ...
3
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0answers
2k views

How do I determine the Internal Energy of ammonia at a pressure in temperature when the steam table doesn't say it

I just bought a steam table for my thermodynamics class since they don't allow use to use the one from the book for the tests. This one is different from the one in my textbook as it doesn't give the ...
3
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0answers
570 views

Maxwell's Demon - laser cooling

There’s an interesting article on Scientific American that tells how to cool individual atoms to within a very tiny fraction of Absolute Zero. It uses two laser beams acting on a very cold rarified ...
3
votes
1answer
100 views

Quantum flux tubes possible shapes

If given energy, can flux tubes be any shape as long as all quarks are connected and the amount of energy is insufficient to form a quark-antiquark pair, or will the shape of the flux tubes be a ...
3
votes
1answer
2k views

Is Energy attracted to Energy?

Newton taught us that bodies with mass attract each other according to the universal law of gravitation (mass-mass attraction) and Einstein taught us that mass and energy are equivalent though his ...
2
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0answers
24 views

A Spontaneous Reaction with greater ordering

I wanted to ask a question regarding entropy in a reaction. I was given the reaction $2H_{2}$ (g) + $O_{2}$ (g) $\rightarrow$ $2H_{2}O$ (l) and asked: the overall process is spontaneous but ...
2
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0answers
45 views

Are conservation of mass and conservation of energy *independent* constraints for physical systems?

I'm modeling fluid systems and want to use conservation of mass (aka 'continuity') and conservation of energy as constraints to help solve for certain system parameters. But it occurred to me that the ...
2
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0answers
31 views

How much energy does it take to magnetize a neodymium magnet?

I read somewhere that when neodymium magnets are made they are subjected to intense magnetic fields in order to magnetize them. So lets say we have a cubic neodymium magnet that is .5 by .5 by .5 ...
2
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1answer
53 views

What is the information concept and how can it be measured,…?

According to the Wikipedia, ""Information of an entity is that which resolves the uncertainty of its properties"" source: Wikipedia, physical information Information contained in a physical ...
2
votes
1answer
48 views

contradiction between total photon energy in the universe and early matter antimatter ratio

When looking at the energy count in the Universe, on one hand we are told dark energy 68%, dark matter 27%, regular matter 5%, neutrinos and photons a very small fraction (trace like). https://en....
2
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0answers
59 views

Hamiltonian directly expressed in $(q,\dot{q})$ : how to find what is $p$?

I am reading a book about non relativistic quantization of E.M field. But first we do classical field theory. We directly wrote the Hamiltonian of our study, and a part of our Hamiltonian is the ...
2
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0answers
46 views

Questions about the energy density and momentum density in linear media

Precisely which energies are accounted for in the energy density of a linear medium given by $$u = \frac{1}{2}\left(\epsilon E^2 + \frac{1}{\mu}B^2\right)?$$ For example, is there a kinetic energy ...
2
votes
2answers
89 views

Is there a connection between the energy distribution and time dilation?

Can anyone please help me understand what is descibed bellow? Scenario 1. We have a pair of atomic clocks. Let's call them clock A and clock B. We switch both of them on at the same time. Clock A ...
2
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0answers
44 views

How can I draw the energy bands for the first and second zones of Brillouin? Is it conductor or insulator?

I want to draw the energy ($E$) diagrams for a simple cubic cell of parameter $a$, where each atom provides two electrons for the almost free electron levels for planes [100], [110] and [111]. I ...
2
votes
1answer
66 views

What happens to the gravitational potential energy of the objects at the singularity of a black hole?

As they are 0 distance from the center of the gravitational body, do they have no potential energy? Does this mean that the singularity is at the lowest energy state possible? Sorry if this sounds ...
2
votes
3answers
80 views

Does a spring's $k$ affect the acceleration of a coupled mass?

Suppose I have a spring of spring constant $k$ attached to a mass $m$, with a constant force $F$ applied to the free end of the spring thus accelerating the mass. What happens to the acceleration of ...
2
votes
1answer
348 views

On Joule's free expansion experiment

While reading through an introductory textbook in Thermodynamics, I've come across a series of arguments that seem somewhat arbitrary/vague, on which I'd like some clarification. To begin with, the ...
2
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0answers
101 views

Percentage increase in wavelength leads to percentage decrease in energy. (Compton effect)

In this question: What percentage increase in wavelength leads to a 75% loss of photon energy in a photon-free electron collision? My understanding of this question is that $0.25\times E_i = E_f$, ...
2
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0answers
50 views

Hydrogen energy state transition times and probabilites

How correlated is the energy absorbed to the later energy emitted, and hence to the transition type? What is the scale of time it takes to make a downward transition in energy level? In a very cold ...
2
votes
2answers
89 views

Partitioning the kinetic energy into components in relativity

In classic physics, kinetic energy is defined as $$ KE = \frac{1}{2}m v_x^2 + \frac{1}{2}m v_y^2 + \frac{1}{2}m v_z^2 $$ So, by defining $ KE_x = \frac{1}{2} m v_x^2 $ , $ KE_y = \frac{1}{2} m v_y^2 $...
2
votes
0answers
228 views

Does an electron have a frequency (and hence an energy)?

The formulation is provocative, the question is similar to the question here. There I can follow the question, but not the answers, which for me imply that an electron in a momentum eigenstate does ...