# Tag Info

## New answers tagged thermodynamics

0

Use heat pipes. They work in large lengths far better than anything else. They can transfer far more heat than anything else. It is a pipe with some sort of porous wick coating the inner surface of the pipe that transports the liquid back to the hot end. At the hot end the liquid evaporates and travels down the center of the pipe and condenses at the cold ...

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Empirically the Altitude/Pressure where sound stops propagating can be determined in a Hypobaric chamber. Simply place a sound emitting device in the chamber with a microphone. A mercury manometer on the chamber can determine the 'altitude' where sound stops being transmitted to the microphone.

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Thermally insulated tells you go for Stefan. Newton's law of cooling is for convection transfer. Don't confuse stuff. Maybe you missed the term "made of the same material", you should conclude the relation in their surface area.

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You misunderstood le chatlier principal. By saying that" its effect to reduce", it meant causal effect is to be reduce. So, here he meant on increasing pressure since volume decrease , here he meant to move from more volume towards that direction which has less volume, where increased pressure has less effect. He hasn't decreased volume , decrease in volume ...

1

When normalized, $A$ is just equal to $1,$ so that $f(E)$ varies between $0<f(E)<1.$ Addendum for the edited question: The prefactor $\frac{2}{(2\pi\hbar)^3}$ crops up in the volume integration of density of states performed in k-space for the computation of number of states $N$ (i.e. all available energy states up to a certain maximum (fermi level) ...

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The Second Law of Thermodynamics is an approximation, it has statistical or probabilistic validity. Statistical Mechanics corrects the plain flat out version of it that says entropy never decreases to the following. The overwhelming majority of the time, a sufficiently large system which is not a closed system (in the sense of mechanics: note that in ...

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The summation indices on $Z$ must match the summation indices on $\bar{E}$, because $Z$ is the normalization constant for the total probabilities of being in every state. The $n=0$ state has zero wavenumber and doesn't exist. You're right to discard the analogy with para hydrogen. In that case, the peak is caused by interaction of the nuclear spins of the ...

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The work being done on the surroundings is because the air parcel expands as the pressure decreases. There would be some heat transfer if the parcel of interest has a different temperature than the surrounding air. This effect is smaller because gases are poor conductors of heat, as mentioned by @gerrit. We take advantage of this with fiberglass and ...

1

You can circulate chilled water through the pipe which should distribute the temperature. Rate of circulation, along with the thermal properties of the pipe and embed media will control the precise temperature gradient - if thats even important for your application. Lastly, the problem of steady state temperature distribution in a metal rod is well ...

1

Newton's law of cooling is a corollary of Fourier's law of heat conduction: $$q=-\kappa \nabla T,$$ where $q$ is the heat flux, $\kappa$ the heat conductivity and $\nabla T$ the temperature gradient (in a single dimension $\nabla T=\frac{dT}{dx}$). In essence this law tells us that heat flows from hot to cold and that the heat flow is proportional to the ...

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When two quantities of water ($m_1$ and $m_2$) at different temperatures (resp. $T_1$ and $T_2$) are mixed in adiabatic conditions (no heat loss and no external heating during mixing) the temperature $T$ of the resulting mixture can be calculated from the heat balance (no heat is lost or added so the heat contained in both masses is found again in the ...

1

The color of an object says something about its emissivity/absorbance for visible radiation. But it has virtually no correlation to the behavior at IR wavelengths. A white object may reflect significantly more visible light than a black one, but may reflect identical amounts in IR. Since your roof will not be cooling via visible radiation, the color ...

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I'm fairly certain that the energy difference between the two is negligible. Any heat as a result of light absorbed is localized on the roof, with layers of insulation between the inside of your house and the additional heat generated. Most of the additional energy absorbed would heat up the air rather than the inside of your house. Additionally, the optical ...

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Actually the human body emits more than thermal radiation. The Czech military did a study on measuring the extreme low frequency radio band emitted by the nervous system. It can be found on www.measurement.sk by searching Human electromagnetic emission in the ELF band - Measurement ... www.measurement.sk › Lipkova This makes perfect sense when you consider ...

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Here's a heuristic answer that may help. Imagine that water is in contact with an extremely cold ice cube (so the molecules in the ice are barely moving). When a liquid molecule collides with an ice interface, it excites an ice molecule in the crystal structure, causing a small wave to propagate in the material, kind of like how a pulse propagates in ...

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Basically a "molecule" of water cannot heat up ice. I think what you are trying to say is, how does heat transfer take place on a molecular level? If that's the case, then its something like this. In the interface between water and ice, water molecules are moving, while ice molecules are static. on contact, some molecules of ice acquire velocity (due to no ...

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Heat, a measure of thermal energy, can be transferred from one point to another. Heat flows from the point of higher temperature to one of lower temperature. The heat content, Q, of an object depends upon its specific heat, c, and its mass, m. The Heat Transfer is the measurement of the thermal energy transferred when an object having a defined specific heat ...

0

Just take the derivative of the equation of state which is the ideal gas law. $(\frac{\partial V}{\partial P})_T=-\frac{RT}{P^2}$. Now substitute into the original expression for compressibility: $\kappa_T=\frac{1}{V}(\frac{RT}{P^2})$

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From a practical standpoint, some processes can be considered adiabatic because they happen so quickly that there isn't time for any substantial heat transfer. The best common example of this is the process inside the cylinders of your auto engine when the spark plug ignites the air-fuel mixture. The resulting combustion, compression, and expansion work ...

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No. A low entropy "initial state" could be the result of a so-called anthropic fluctuation in a (past) eternal universe. Fluctuations about equilibrium could, fortuitously, create the initial conditions for life as we know it. This was proposed by Boltzmann and his assistant Schutz in the late 19th century, though ultimately deemed unsatisfactory by a ...

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At the classical framework , i.e. no General relativity and astrophysical observations of the 18th century , this is a valid question. When talking of a "Universe" one must have a model , and the model depends on the state of physics knowledge at the time of the model. The second law states that entropy always increases or stays the same. One can make a ...

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Hamurabi, I assume you are asking for the order of the wave equation. Try thinking about intramolecular vs. intermolecular forces. A wave equation is necessary to describe the energy of any quantum occurrence, so far as I recall. It may take an approximation for any non-ideal system, but exact or not the wave equation describes the moment in time when the ...

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Nuclear rocket motors work by heating a gas and allowing it to expand out of the exhaust. To get the most thrust from your gas you want the momentum of the gas molecules to be as high as possible, because the force is equal to the rate of change of momentum of the gas molecules. Suppose the nuclear reactor heats the gas to a temperature $T$, then the ...

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As rockets have finite fuel capacity and important parameter is how much rocket velocity can be achieved in a given situation per unit of fuel mass consumed. The higher the exhaust velocity the more effectively the fuel mass is utilised. Issues such as energy required are also important but generally exhaust velocity or "specific impulse" is amongst the most ...

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The minimal counterexample seems to me to be the following: Take two materials, placed next to each other: ____________________ | | | | Material|Material | | 1 | 2 | ____________________ E1 _ _ _ E0 _ _ They have energy levels as indicated above- both have states at E0 and E1, but one has two excited states. ...

0

The best representative of a black body curve is the cosmic microwave background radiation. Graph of cosmic microwave background spectrum measured by the FIRAS instrument on the COBE, the most precisely measured black body spectrum in nature. The error bars are too small to be seen even in an enlarged image, and it is impossible to distinguish the ...

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Is the Sun absorbing energy from it's surroundings? No, of course not in a net sense. The Sun loses far more energy than it absorbs from its surroundings. It is not in thermal equilibrium. The Sun is also not a blackbody at a single temperature, even though it most definitely absorbs nearly all radiation that is incident upon it. That is because the Sun is ...

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Ultimately, Newton's law of cooling is a simplification that can be obtained from the full heat equation, i.e. $$\rho c\frac{\partial T}{\partial t} = - \kappa \nabla \cdot T.$$ The heat equation itself can be derived from first principles, assuming Fourier's law for heat flow, namely that it is proportional microscopically to the difference in temperature ...

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How do we know that the rate at which a body loses heat is proportional to the difference between its temperature and that of its environment? In classical physics this is a law. "Fourier's law The law of heat conduction, also known as Fourier's law, states that the time rate of heat transfer through a material is proportional to the negative ...

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It appears Newton himself did some experimentation, but failed to divulge exactly what he did - though he said "he used a linseed oil thermometer" and the resulting data. Source: History of Newton's Law of Cooling

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The temperature is really only negative in the sense of the classical definition of temperature. What is actually happening in a population inversion is the particles aren't following Boltzmann distribution of energies anymore. Comparing the temperature of a Boltzmann distributed system to a non-Boltzmann system might not be meaningful at all. People say ...

0

One way to define temperature is via statistical physics. It is a quantity used to describe an equilibrium distribution of possible states via Boltzmann factor. Given a total energy of a classical system $$E(x_1,\ldots,x_N, p_1, \ldots p_N)$$, where $x_1 \ldots x_N$ are the position coordinates, and $p_1 \ldots p_N$ are the momentum coordinates. The ...

-1

Total entropy of the universe is equal to the total area of the space boundary, according to holographic principle. Our universe is expanding, asymptotically approaching de Sitter space. In de Sutter space the radius of the cosmic horizon is constant and equal to the Hubble radius - the distance at which cosmological red shift becomes infinite. For ...

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You've touched on a very important point - "negative temperature" is a misnomer. Start with a simple thought experiment. Physics tells us that temperature changes happen continuously. In order to change from 10K to 20K, we must first pass through 11K, 12K, and all other intermediate temperatures. In order to achieve a "negative temperature," you would need ...

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It's simple. You can think of temperature as being the standard deviation of KE among all components (atoms) of a mass. This is significant because KE is a relative quantity, but temperature is absolute, and this relationship makes that possible. If all atoms are moving uniformly in the same direction, then the temperature would be 0.

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You are correct. The temperature is usually defined in terms of random motion of the atoms. This announcement from NIST talks of an atomic beam cooled to $30 \mu K$, so there is very little random energy. It doesn't give the speed of the beam, but that could be very high if the atoms are all moving in the same direction.

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I think you are right. A perhaps more precise relation between temperature and velocity is the Maxwell–Boltzmann distribution: \begin{equation*} P(\textbf{v}) = \left( \frac{m}{2\pi k_B T} \right)^{3/2} \text{exp} \left[-\frac{m ( \textbf{v} - \textbf{v}_0)^2}{2 k_B T} \right]. \end{equation*} where you see that the mean velocity $\textbf{v}_0$ and the ...

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I think your view is correct, and you can think about the following real word example. In labs here on earth, we can use laser cooling techniques to cool atoms to $\mu$K scales in the lab frame. But the lab is on earth, and the earth is moving very fast around the sun, and the sun is moving very fast around the galactic center and so on. We don't take ...

-1

I don't think it is wrong to think entropy is correlated to disorder specifically for the example your teacher gave provided there should not be any ambiguity in defining disorder. There is an increase in entropy when you shook the marbles in the jar, but it is really, really, really negligible. However, energy dispersal method is far more intuitive & ...

0

Isobaric processes usually occur when a system is put in contact with a pressure reservoir, i.e. a system with a given pressure that imposes its pressure on all the other systems in contact with it. A common example of pressure reservoir is the Earth atmosphere: if you put your system in contact with the atmosphere it will acquire its pressure ($1$ atm); ...

2

In this case you are taking energy from a body, of finite heat capacity(its not a heat reservior) ,doing some work and dumping the remaining heat energy into a heat sink, say the atmosphere, at temperature ${T_0}$ (which can be assumed as an ideal heat sink with infinite heat capacity). Since temperature of water is changing , carnot engine changes its ...

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Without more details, we can't find a specific case that will match what you are doing. However, I did find a decent example to show you what to look for to answer your question. Data for a nearly-sonic round jet can be found in this paper. If you look at Figure 5(a), you'll see how the normalized centerline velocity from several experiments collapses ...

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Making the total entropy tend to zero, makes the efficiency tend to the carnot efficiency, which is indeed the maximum efficiency for a cyclic process , according to carnot's theorem

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The answer lies in changes in Gibbs Free Energy: $$\Delta G= \Delta H -T \Delta S,$$ where $G$ is Gibbs Free Energy, $H$ is Enthalpy, $S$ is Entropy and $T$ absolute temperature. When we stretch the rubber band it heats up due to viscous friction of the molecules sliding over each other as we stretch the object. It as nothing to do with with adiabatic ...

2

Therefore, when we say, for example, that the energy of the ideal gas at temperature T is E=32NkBT, we should really be saying "the energy of the ideal gas immersed in a heat bath at temperature T"? Is this reasoning valid? This is true. What is also true is that you can also say that the temperature of the (completely isolated) gas of energy E is T=2/3 ...

0

OK, sorry for the confusion, only now maybe I really understand your question. The answer is probably as simple as this: when you stretch the band, the molecules of the rubber band actually move (or fluctuate) faster. Why they move faster? You can think of a string, one end is fixed to the wall, the other is at your hand. In the middle of the string you have ...

0

No, they will cool at different rates Newton's law of cooling states that $$\frac{dQ}{dt} \propto T-T_{env}$$ where $T$ is the temperature of the water and $T_{env}$ is the temperature of the environment. As you can see, the larger the temperature difference, the more quickly the water will lose heat. We can assume that the specific heat of water will ...

1

I don't believe that the thermal conductivity of most metals is very sensitive to magnetic fields. Yes, there will be some field-induced band shifting in the case of an itinerant ferromagnet which, in principle, leads to a change in the density of states at the Fermi level, but that will typically be a very small effect. If the magnetic field induced ...

2

Magnetic fields certainly can influence thermal conductivity. This shows up, not surprisingly, when there is a strong influence of the magnetic field on other properties, particularly electronic ones. One (non-metal) example is 'Thermal conductivity tensor in YBa$_{2}$Cu$_{3}$O$_{7-x}$: Effects of a planar magnetic field' by R. Ocana and P. Esquinazi, Phys ...

1

Answer 1. As its isothermal so the temperature remains constant. So the change in internal energy is 0. Answer 2. Its formula is $W = -nRT$ $log_e(P_i/P_f)$ Putting the values we get $W = -4012.6497831$ Here $W$ is work done on the system

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