New answers tagged

5

No, not really. The amount of entanglement and the amount of energy in a state are completely independent: entanglement (together with discord) is a property of the state itself and its relationship to a bipartite (or multipartite) structure of the Hilbert space in which it lives, whereas energy is a joint property of the state and the system's Hamiltonian....


0

At 100 dB, the sound pressure level is 2 Pa. At normal atmospheric pressure ($10^5~ \rm{Pa}$), that corresponds to a change in pressure of ±0.002%. If you have a "closed" head phone - that is, the total amount of air in the headphone is roughly constant - then you can translate the question into "how big of a displacement of a 3 cm piston will change the ...


1

You are totally confused in doing this computation. In your computation, you're plugging in the gravity of the Earth. That's not the relevant force acting on the car, which is friction, coming from both the air and the tires. It's easy to see what's going wrong when you draw a force diagram: gravity pulls the car down, but it's counteracted by a normal force....


1

$$g(E)=\text{number of states at energy E available to be occupied}$$ $$f(E)=\text{probability that a state with energy E is occupied}$$ so that $$g(E) \ f(E) = \text{average number of occupied states with energy E} \\ =\text{average number of particles with energy E} = N(E)$$ So that the total number of particles will be given by $$N=\int N(E) \ d E$$ ...


0

What you are saying does make sense, and ties in with some of the points made in What makes running so much less energy-efficient than bicycling? Although you mention "putting a lot of energy into making the Earth flat", I do not think you are making an economic argument. You are merely asking if the superior efficiency of cycling is due to the fact that we ...


0

If a body (substance) has zero kinetic energy then we should suppose that it is a perfect crystal at absolute zero and all motion is in the vibrational ground state if it is a molecule. If an atomic solid then only zero point motion in the lattice. So yes it has a temperature. The potential energy is that within and between the molecules or atoms. In your ...


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I've found that this design, called field coil alternator is widely used in automobile generators. So they must be efficient enough for industry.


2

Any quantised system has a ground state and excited states, and in any quantised system relaxing into the ground state requires energy to be shed in some fashion. In an isolated system like a hydrogen atom the energy is normally emitted as photons. However add other hydrogen atoms and this opens new routes for energy to be lost. For example an excited ...


1

I may be wrong, but I think Lenz's Law might provide an answer. The circuit with the straight wire takes in current i(suppose) once the switch is closed. The one with the looped wire, will having a changing flux through it once the switch is closed. Since any change is to be opposed, the current drawn this time will be less,(assuming the dimensions of the ...


2

For a general closed systems containing only a single chemical species, you have, if you express $U$ as a function of its natural variables $\{S,V,N\}$ $$U=U(S,V,N)=TS-PV+\mu N$$ from which we obtain $$d U = \frac{\partial U}{\partial S} dS + \frac{\partial U}{\partial V} dV + \frac{\partial U}{\partial N}dN=T dS - P dV + \mu dN$$ $U$ is a function of $\{...


1

Okay I'll have a go at answering this, although it may be a make belief scenario. Looking at where you got your inspiration from, he stated using a magnet as a core for an electromagnet, so your curiosity must have piqued from the idea that the wire carrying electric could itself be magnetic. Because of polarization and magnetization, all the magnetic ...


1

But for an ideal gas, internal energy is only a function of temperature and so internal energy remains constant here,no change in average kinetic energy of gas particles takes place, so where does the chaos come from to increase entropy of the system. 'Chaos' is not a very well defined term in context of statistical physics. It is not necessary to use it ...


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The chaos comes from by changing of volume or pressure of the system. The average kinetic energy doesn't change, but number of collisions increases (if pressure increase) or length of paths increases (if volume increases).


3

In simple terms the internal energy can be thought of as the sum of the kinetic energy and the potential energy of the molecules. The kinetic energy of the molecules depends on the temperature - a higher temperature means that the molecules have more kinetic energy. The potential energy of the molecules depends on the bonds (interactions) between them - ...


1

You say "rolling without slipping." But what do you think will happen in this situation? Do you think the large disk will "roll without slipping"? Can you do an experiment at home to find out? You can use whatever method gets you to the correct answer. You are given forces (F, weight) so try using forces. Try solving the equations lucas gives you. ...


1

Transmit the force $F$ to the center of mass and add its torque. Consider to the relative motion between disc and ground. Then you can recognize the correct direction of friction force (friction force opposes relative motion). Free body diagram of disc is as below. (See this answer to understand better.) Equations of motion are: $$F-F_f=ma$$ $$N=mg$$ $$...


2

It is not true that the same force has to create the same change in kinetic energy. For instance, if two equal forces of opposite directions are applied on a body, the body does not change its energy. Thus each force makes zero work, or zero change in kinetic energy. You could tell that both forces create kinetic energies in different directions and that ...


2

Energy is force times distance. You haven't specified a distance, so you can't say how much energy that force delivers. If you allow the force to rotate the sphere, the application point will accelerate faster than it would if the sphere does not rotate. So a constant force will deliver energy to the sphere faster than it would in the non-rotating case. ...


4

There was a lot of hype $10$ to $15$ years ago over the hydrogen economy. It was of course rather odd that anyone could take this seriously. How much free hydrogen gas is available? Answer: virtually none. The problem is that you have to either put electrical energy into water to split it into $H_2$ and $O_2$, or if you chemically condition methane $CH_4$ ...


1

$f(E)$ is the probability that a quantum state of energy $E$ is occupied. There are two quantum states (for two spin states) at each energy. The probability cannot be doubled, since that could then exceed 1. All that happens for a spin $1/2$ particle is that the number of available quantum states is doubled.


1

Your confusion arises from the fact that you are confusing scalars and vectors. Scalars, are like numbers, and they have only magnitude. Vectors on the other hand have direction in addition to magnitude. In your question, you mention the wave vector, which, as its name suggests, is a vector. Typically vectors are written in bold or with an arrow over them; ...


1

The values of $E_c$ and $E_v$ in the band diagram depend on the point of reference. So yes they can have negative values if you chose your reference that way. Keep in mind that their difference $E_g$ stays constant nonetheless. Electrons are fermions and therefore governed by Fermi-Dirac statistics. That means that they have to comply with the Pauli ...


0

The term van der Waals force is a catchall for several different kinds of forces. However all of the forces are due to electric dipoles, and the strength of the force is related to the dipole moments of the interacting molecules. The strongest interaction is when both interacting molecules have a permanent electric dipole. For example water molecules have a ...


0

actually you got it wrong work energy theorem states that the net work done is equal to change in k.e here you have to concentrate on the word net .. because net work done work done by you and work done by frictional force is zero......


3

In theory there is no lower limit on the amount of energy that must be exchanged to make a measurement, at least directly. But you are constrained by Landauer's principle when you initialize the memory you need to record the measurement. Effectively the measurement is the replication of information about the measured system's state in the measurement system'...


0

There are two kinds of energy to keep track of: potential energy and kinetic energy. Work can be thought of as the change in energy (because of the "work-energy theorem"). And the key question to ask while the weightlifter keeps his weight in the air is: is there a change in energy? Kinetic energy is a function of movement. If there's no change in ...


0

When the weightlifter lifts the mass he does work and transfers some energy to the mass which is stored* in the mass as potential energy. Once the bob has been lifted the weightlifter applies a force to keep the bob lifted (to counter the force exerted by the mass downwards i.e. mg) but does no work as the force does not cause any displacement. Edit: *No ...


0

From the wiki article on the sun's radiation: Solar irradiance spectrum above atmosphere and at surface. Extreme UV and X-rays are produced (at left of wavelength range shown) but comprise very small amounts of the Sun's total output power. You ask: My Question is, why exactly does the intensity vanish below 240 nm ? If i look at the plank's law, ...


-2

Yes, any constant should be ignored.


2

This is known as the "Heat Death" of the Universe which is based on the Second Law of Thermodynamics which says that Entropy will increase in an isolated system (and, we assume the Universe is isolated). So, as Entropy increases over time then ultimately every part of the Universe will be at the same temperature and same level of maximum Entropy such that ...


6

In many cases, you can see laser cooled atoms in a MOT with the naked eye. They look like a little fuzzy glowing dot at about the same color as the trapping laser. So there are indeed lots of photons leaving the system. This spontaneously emitted light is what ultimately carries away the entropy and make cooling possible. You could try to capture this ...


2

Laser cooling works by irradiating a e.g. an ensemble of gas atoms with light that has slightly less energy than a excitable transition in the atom. If the frequency is chosen right, the transition is only addressable by a 2nd order process which will consume kinetic energy from the atom. If I understood your question right, you are asking what is happening ...


-2

Kinetic energy and photon absorption Particles - when moving into a magnetic field - have gained before kinetic energy. As GRB wrote: Every time a charged particle has to be accelerated, a photon has to be involved. If you want to linearly accelerate a charged particle, you have to shoot photons at its back. To be precise this one of the possibilities ...


1

First, let's pick a field to work with, because particles act differently in different vector fields. Let's say we're dealing with a charged particle in an electrostatic field. EM fields can be seen as a deformity in spacetime, the field is warping the space in which it is defined. In fact, for advanced EM we use tensors to describe electromagnetic ...


1

First of all, we must be talking about a field that would affect (exert a force on) the object (like a charge in an electric field or an object with mass in a gravitational field). Now, what does potential energy mean? It is a measure of "stored energy" in the system. That means, if you released it, this energy would be released. Put a book on a shelf and ...


0

It is important to note, that you are totally skipping the kinetic Energy $T$ part. The total energy of a system is given by $E=T+U$. There are several examples of systems which build up potential Energy over time. Some examples are: The mass of a pendulum is constantly cycling the total energy between kinetic and potential energy Objects orbiting a center ...


-8

Since no nuclear bomb has been used since since Nagasaki we can and indeed do only infer "applications" if you are talking about dropping a nuclear weapon on a human population. These estimates based upon the criteria you have given appear very effective as no theronuclear weapon has been detonated on a population center since Nagasaki, Japan in 1945. I ...


24

The so-called TNT equivalent of a nuclear weapon is an unambiguous way of quantifying how much energy is released by the nuclear weapon. There's nothing 'wrong' about it. The only caveat is that the damage caused by, say, Little Boy versus 15 kilotons of TNT would not be identical despite having an equivalent yield (for various practical reasons). ...


1

In order to input in your terms 500rpm you are required to input the actual shaft rpm Plus 500 you seek to add. You must charge your input to the systems energy level. So to answer your question yes your input of 500rpm would slow down the shaft rpm.


0

I know the final kinetic energy is 0.1566J How did you find the final kinetic energy? To find the final state of the system you have to assume that there are no external torques acting on the system and that angular momentum is conserved.


3

Considering to your question and comments below it, I think that you have been confused about some assumptions. For example, when we assume that there is no friction, you should be able to imagine a situation that there is no friction in that. You shouldn’t imagine real life for that assumption, because in your common daily life, you cannot find a perfect ...


2

To put this simply, the work-energy theorem states that The work performed by a force $\mathbf F$ over a distance $\Delta \mathbf r$, $W=\mathbf F\cdot\Delta \mathbf r$, is equal to the change in kinetic energy $\Delta E_\mathrm{kin}$ of the relevant object. If the inner product $\mathbf F\cdot\Delta \mathbf r$ is negative, the force is acting in the ...


-1

No, we can't. I assume that you are talking about a moving object and therefore kinetic energy. You Can apply a resistive force, therefore slowing the object and reducing its energy. But as soon as the object reaches zero energy (read: kinetic energy), the body will be at rest. If you continue to apply the same force, from Newton's 2nd principle, the body ...


0

there are two types of vacuum in physics. one with and one without radiation (radiation being any kind of electromagnetic interaction, or photons). Sloppy scientist call a matterless volume vacuum, although it still has radiation (and therefor contains energy). You can imagine that it is very hard to achieve a true vacuum in which only the vacuumfluctuation ...


0

I like the following explanation. Although mostly mathematical, it illustrates a point Feynman tried to convey in his lectures. Energy is always conserved, and whenever it seems like it isn't you just need to look harder. Let's recall that in the context of classical particle mechanics one defines the energy of the system of $n$ particles as the sum of the ...


0

The lower level of laser transition is above the ground state,this means that the fast non-radiative transfer from the lower laser level to ground state keeps a reasonable population in the upper laser level(3rd) which is fundamental for lasing.Hence its more effective than 3-level system


1

Tl,dr: Entropy is the right definition, because it's incredibly useful in the description of statistical and thermodynamic systems. Whether or not it quantifies "disorder" in whatever sense of the word is completely irrelevant - it just so happens that it can be interpreted that way. Entropy is not a measure of disorder. At least not really. Then again, ...


3

Possibly you are mixing different concepts together. A short answer is the following: indeed, for a single photon, the energy is proportional to its frequency. That is \begin{align} E_{singlephoton}=h\nu. \end{align} However, for a wave package or an electromagnetic wave, the total energy is proportional to the photon number, $n_{photon}$, as well. That is \...


0

Actually, it depends on the theory you use. In nature, however, all bound states, except for ground states, have natural width, so, strictly speaking, they belong to continuous spectrum. As for theories, the same is true for quantum electrodynamics.


0

Why a free particle gives rise to Continuous Spectrum energy eigenvalues where particle in the Bound States provide the quantization? The real answer is , because that is what has been observed experimentally. Because of the observation of the photoelectric effect, the spectrum of light from specific elements, ( and black body radiation) it became ...



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