Questions tagged [thermodynamics]

Covers the study of (mostly homogeneous) macroscopic systems from a heat/energy/entropy point of view. Consider also using tag: [statistical-mechanics].

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How do I determine the relationship between initial and final volume in this case?

Some total volume contains two compartments separated by a wall that allows for mechanical and thermal interaction, each compartment having a different amount of an ideal gas. For the initial ...
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Understanding the derivation of the variational principle in classical density functional theory

I am trying to understand the derivation of the variational principle as presented in Bob Evan's 1979 work.[1]. The part that is tripping me up is when he presents the following result. He starts by ...
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Would water flow in the following system?

Would water flow in the following system?
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How do you make light?

We make light making a charge oscillate, or heating a body. Are there differences between the two processes? But, above all, are there other ways in which we can produce em radiation?
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What properties of a mixture can be calculated?

Some properties of a mixture can be calculated by using $X=\sum_{i=1}^n n_i X_i $, where X is a property of the mixture, $n_i$ and $X_i$ are mole fraction and property of the ith component. The ...
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$\rm CO_2$ Car Back Wheel Thickness [closed]

For my physics class I'm designing a $\rm CO_2$ car from scratch, and I was wondering why most cars pictured online have wider back wheels than front wheels, and I'm confused at why that is. My ...
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Does gas pressure impact the rate of evaporation?

As we know, evaporation occurs when a liquid molecule has a kinetic energy that is greater than the minimum amount of energy needed to overcome the intermolecular attractive forces holding it in the ...
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Do Maxwell's equations still apply in fluids?

Hi I am trying to build an electrical impedance tomography platform. The problem I'm facing mainly is to come up with an algorithm to calculate the variation of conductivity within the lung tissue ...
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Temperature of a rotating/charged black hole

How do you calculate the temperature of a rotating or charged black hole? How will rotation/charge affect the lifetime?
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In the Statistical Mechanics Mark E. Tuckerman 4.4.7

When deriving the energy fluctuations in the canonical ensemble, a step is made to approximate Cv≈N, why is this?
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Proof that minimum free energy corresponds to equilibrium

I've tried to derive the relation between free energy, $F$, and equilibrium of a closed system. From the derivation i've written below it seems that if $T$ is constant and the system can't exchange ...
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How best to maintain the temperature of a swim spa?

All the advice I have seen on the internet suggests that it is more economical to keep the thermostat of a hot-tub at its intended temperature, rather than turning down the thermostat when the tub is ...
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Is it possible for a thermoelectric generator to not have a heat source or heat sink?

Specifically, the type of thermoelectric generator I am suggesting makes use of the ExB drift effect. When electric and magnetic fields are perpendicular to one another, with infinite mobility of the ...
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Why do most metals have high thermal expansion coefficient although their thermal conductivity are generaly high?

the relationship between thermal conductivity and thermal expansion in metals. Why do most metals have high thermal expansion coefficient although their thermal conductivity are generaly high? Please ...
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Clearing up concepts regarding quasi-static processes

I have two main questions/problems: Most definitions I've seen about quasi-static processes talk about them being "infinitely slow processes", or "slow enough as for the system to ...
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Quantum versus Classical Partition Function

I am confused as to which partition functions are classical and which are quantum. I am interested in the canonical ensemble. Several places I have seen the "classical" partition function as:...
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Nuclear Propulsion System

In a fictional sci-fi setting , is it plausible to: Have a huge nuclear powered aircraft carrier to be propelled by H2-O2 rocket engine (size adjust) where you generate both from sea water on the fly ...
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How much can gases expand when heated? [closed]

When heated, how much can a gas expand when heated relative to Temperature? Is there any physical limitation to how much it can expand, at maximum? What if gas is contained in a sphere or cube, how ...
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An ideal gas expands into vacuum in an insulated rigid vessel. Which of the followings happens? [closed]

This question came in the Dhaka university admission exam 2018-19. An ideal gas expands into vacuum in an insulated rigid vessel. Which of the following happens? A. no change of internal energy B. a ...
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What law of thermodynamics is broken here? [closed]

This question came in the Dhaka university admission exam 18-19. A heat engine in each cycle does positive work and loses energy as heat with no heat energy input. Which law of thermodynamics does the ...
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Analogy between Curie's Law and the Ideal Gas Law

I've been trying to derive Curie's Law from the Ideal Gas Law for a while, since numerous sites on the internet state that they are analogous. However, if we apply the equivalences - $P \iff B$; $V \...
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Unable to make sense of - Heat, a form of energy [duplicate]

I have referred to some textbooks on Thermodynamics and they more or less explain heat in the following manner: Consider a system which has some energy content. In order to increase the energy content ...
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Where does all the energy in black holes go?

The temperature inside of a black hole is almost absolute zero, so particles inside a black hole have almost zero motion. So if they don't give out any heat or light, where does all the energy it ...
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Expected energy in micro-canonical and canonical distribution

Which relation $E(β)$ is required to ensure that he micro-canonical distribution and the canonical distribution have the same expected energy?
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Physics of the convection oven

I don't understand how convection ovens can cook food faster than radiant heat ovens. Guides to convection ovens claim that they cook food 25-30% faster than radiant heat ovens, but do not really ...
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In an isothermal process there is no change in internal energy, but why in an isobaric one?

In an isothermal process, the heat Q added (which increases the temperature and internal energy) is exactly cancelled out by the work W done by the gas in the environment (which lowers the temperature ...
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How can I model basic heat transfer in a partial vacuum?

If we imagine an object in a vacuum chamber being heated, how can this be modelled? There would be three heat flows to the object: (1) by convection/conduction of the air, (2) by radiant heat from the ...
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Enthalpy, why is work only partially done?

If a system with const. pressure can change it's volume free, a heat transfer into the System results in a partial work done, which gives back the inner energy addet partial back to the environment. (...
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Why is it so much harder to keep the same room cool than to keep it warm?

I have read this question: Let me offer a different perspective on this. Cooling is not universally harder than heating. Why is cooling much harder than heating? Now I have noticed that whenever in ...
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Is there a temperature difference when I change the volume instantaneously? [duplicate]

If I were to instantaneously remove the wall as drawn above, then there is no loss of molecular velocities --> T1 = T2. But I have a problem imagining that there really is no change in temperature. ...
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Lifting force and rope tension in the elevator [closed]

İn the beginning T1 = 10N and T2 = 10N. If the elevator starts to move downwards with acceleration a = 2m/s², what values ​​do the tensions in the ropes take T1 and T2, respectively? (The answer is A ...
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A generator needs to heat up water to make steam. Should this generator be in denser atmosphere or less dense? [closed]

I was thinking about in the future. We can have underwater geothermal plants that use a metal rod stuck deep into the earth to conduct the heat from lava which will heat up water into steam and power ...
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Do microwaves make polar molecules spin or vibrate? [duplicate]

I’ve been reading about how microwave ovens heat up your food and I keep finding conflicting answers (some say it vibrates, others say it spins). On the one hand, I’ve also read that heat is the ...
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What is the time required to heat a fluid inside a cylindrical container? [closed]

. There is a container of total volume 36000 liters, which is meant to store fluid in it. The fluid must be maintained at a certain temperature for which steam is used to heat the fluid but the ...
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How can we prove each energy in different condition become minimum when thermal equilibrium

My question is like the title. We know in condition : const volume, entropy -> internal energy(U) reach minimum when thermal equilibrium. condition : const pressure, entropy -> enthalpy(H) ...
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Would a grounded copper heat sink located near a room's ceiling be an effective way to reduce a room's temperature?

I am thinking about a cheap but effective way to reduce the temperature of my bedroom in my apartment during hot summer nights. I live in an old apartment building and the air conditioner located in ...
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In order to explain a reversible change in thermodynamics, why is the following description irreversible?

I have a book that explains reversible processes as follows: A reversible change in thermodynamics is a change that can be reversed by an infinitesimal modification of a variable. [...] Suppose a gas ...
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Do I have enough information to figure out the pressure in this problem? [closed]

The problem goes as follows: A 20 L volume of air isothermally compresses itself until it reaches a volume of 4 L. The temperature is $T=293.15 \ \mathrm{K}$. The initial relative humidity is 60%. ...
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How to find external surface temperature with unknown heat transfer coefficient?

I am trying to calculate the thickness of insulation required for a certain design. The known properties are the inside temperature, target surface temperature and thermal conductivity. From what I ...
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During the breathing process, inhale 3 L of air at a temperature of 0 ° C [closed]

During the breathing process, inhale 3 L of air at a temperature of 0 ° C. Assuming that the pressure in our lungs is p = p atm, determine the amount of heat the body must provide to keep the air warm ...
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What is the meaning that net result is weight has lifted and we can use it to lift other things in the last lines of this paragraph [closed]

Consider weight-lifting machines—machines which have the property that they lift one weight by lowering another. Let us also make a hypothesis: that there is no such thing as perpetual motion with ...
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Is this area a proper visualisation of the heat and internal energy change in a $P,V$-diagram?

The area under the curve in a $P,V$ diagram is the $W$ work done by the system, i.e.: Where the yellow area is the work done by the system in going from point A to B. The internal energy of an ideal ...
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Net force exerted by pressure

Why do the net force $K$ exerted by the pressure of a hard sphere gas according to the Maxwellian distribution on the walls of the container $A \subset R^3$ vanishes? (In the absence of external ...
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Slope of constant pressure line on $T$-$S$ plot

Is slope of constant pressure line is same or di in liquid region and super heated region for pure substance on $T$-$S$ diagram?
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Does statistical mechanics imply that the universe is probabilistic?

Statistical mechanics says that a system will evolve to a state of higher entropy (i.e. states with higher number of microstates) simply because it is overwhelmingly more probable than evolving to a ...
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How is the Big Bang compatible with the preservation of quantum information?

As detailed at https://en.wikipedia.org/wiki/No-hiding_theorem , in the quantum world, information cannot be created or destroyed. The Bekenstein bound limits the amount of information that can be ...
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Magnetization and thermodynamics [closed]

A magnetic needle is placed such that the magnetic field is parallel to its axis. I need to prove the following relation between the specific capacities where $M$ is the magnetization and H the ...
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Why are my pavers still wet? [duplicate]

I sprinkled salt on my pavers to stop the weeds growing but now they stay wet a lot longer. I expected the opposite because Adding salt to water makes it boil faster. Adding salt to icy roads melts ...
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Where does an electromagnetic wave's energy come from?

tldr; doing work on a neutron would only increase kinetic energy, but doing work on a proton would increase kinetic energy as well as emit energy in the form of EM waves. How does that work? I know ...
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Is 'heat has only sources, no sinks' an equivalent formulation of the second law?

I was thinking about it and in a sense heat is an interesting quantity that can only be created and not destroyed. In comparison with the first law this means that ultimately for a closed system all ...
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