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

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If an Ising model is in contact with two thermal reservoirs, would it still experience a phase transition if one of the reservoirs is below Tc?

For example; Two reservoirs are at each end of a one dimensional or even two dimensional lattice. One of the reservoirs has the temperature T < Tc. Would the lattice site have a phase transition ...
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84 views

Will physics ever be able to answer the question: “What caused the universe to come into existance”? [closed]

Or is this just the flip side of a metaphysical question "why does the universe not exist", if the opposite was the case and nothing existed i.e. a universe devoid of all energy, matter forces, ...
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64 views

Thermodynamics equation that involves time? [closed]

There are principles in thermodynamics—e.g., that heat transfers from hot to cold—and equations like $$Q=mc\Delta T,$$ but is there any equation in thermodynamics related with time?
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26 views

Does less heat equals more reflexion? [duplicate]

Does colder metal reflect more if hotter metal reflect less? Why?
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74 views

Why is the derivative of the Fermi-Dirac distribution negative?

Why the derivative of Fermi-Dirac distribution function at absolute zero temperature becomes negative of Dirac_Delta function. The Fermi-Dirac distribution function is \begin{equation} ...
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36 views

Do liquids creep from cold to hot like gases?

Consider the U-tube water experiment below with the left red block at 10C and the right red block at 90C. I think the right level will become about 3% higher than the left level simply because hotter ...
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22 views

Internal energy of a body

I have a really fundamental question regarding the internal heat energy of a body. From textbooks, we know: $$\Delta Q = m \cdot c \cdot \Delta T$$ where $m$ is the mass of the body, $c$ its specific ...
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17 views

Comparing rates of cooling

There are 2 metallic spheres A and B. Mass of A is thrice the mass of B. Both the spheres are heated to the same high temperature from same initial temperature. The spheres are thermally insulated ...
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67 views

Is there a proof that adiabatic processes only occur in thermally isolated systems?

This question arose when I read somewhere that adiabatic processes can only be done in thermally isolated systems and isothermal processes can only be done in thermally non-isolated system. Now, ...
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49 views

¿How does pressure decrease in an isothermal process when heat is transfered?

Let's suppose there is a gas(ideal) inside a cilinder with a frictionless, massless piston. The gas is under a pressure $P_{1}$ and has volume $V_{1}$ at a temperature $T$. We carry out a isothermal ...
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54 views

Calculate thermal expansion from Helmholtz free energy

Is there a way to calculate the coefficient of thermal expansion ($\alpha$) from Helmholtz free energy (A) ? I use the definition $\alpha = \frac{1}{V}(\frac{\partial V}{ \partial T})_p$. With ...
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29 views

Does the aluminization of a Thermos flask matter?

Typically we have a double walled container with a vacuum between the walls which limits or stops conduction and convection heat transfer. They are also (usually) aluminized to minimize heat transfer ...
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114 views

If heat is energy, then why does cooling take energy when it should actually give energy?

Since everything around us isn't absolute zero temperature, and it has heat/energy, then we should be able to use that energy (without temp' difference I mean) and by using that energy (for example ...
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65 views

Understanding the definition of the internal energy

Internal energy is all the energy of a system that is associated with its microscopic components (atoms and molecules) when viewed from a reference frame at rest with respect to the center of mass of ...
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31 views

How does a nozzle behave differently at different velocities of flow?

A converging duct acts as a nozzle for subsonic flows while the same nozzle acts as a diffuser (decelerator) for supersonic flows? How does this actually work?
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57 views

Heating 2 sets of 1L water vs 1 set of 2L water [closed]

Can heating 2 sets of 1L water or 1 set of 2L water have a variation in terms of fuel efficiency? Can one be more fuel-efficient than the other? (migrated from chemistry site)
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49 views

Efficiency in a thermodynamic cycle

Question The area on a PV diagram within one thermodynamic cycle of a heat engine is 610J. THe total thermal energy transferred out of the gas in one cycle is 1300J. Determine the efficiency of ...
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1answer
25 views

Heat, Work and Internal energy in closed systems

This has been troubling me for a while now. I know that the performed work equals $P\Delta V$ for isobaric systems and I know that in isochoric systems no work is done, but how do I find the heat $Q$? ...
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106 views

Why is there a change in entropy in a irreversible isothermic process?

Suppose you have a irreversible isothermal process. The net change in entropy from the system to the surroundings should be 0 if the temperature does not change. So why is there an increase in ...
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31 views

Photon gas, recovering state function from empirical result

Given that for a photon gas the following is true: $$U=3pV$$ $$\mu=0$$ I want to recover a state function $U(S,V,N)$ (or $S(U,V,N)$ or $F(T,V,N)$ etc.) in the most direct, simple way. So far I got ...
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35 views

Black body in thermal equilibrium

In the answer of an exam said that a black body in thermal equilibrium with it's surroundings won't emit any energy, but I don't really understand why. My logic is that every object emits ...
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129 views

How is isothermal expansion/compression physically possible when it assumes heat flow between equally hot bodies?

An ideal Carnot engine is composed of two reservoirs and a working fluid. The hot Reservoir and the cold one have temperatures $T_1$ and $T_2$ respectively, with $T_1>T_2$. The working fluid is in ...
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2answers
124 views

Is air in the refrigerator dry? how much?

I noticed that food gets dry in the refrigerator, so I would like to use this effect to dry some objects otherwise difficult to dry (more specifically: nylon filament for 3D printers, which would ...
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1answer
32 views

BEC in interacting systems

What is your thought on the following statement: "any system of (weak/ strong) interacting bosons, in liquid phase, will form a condensate at T=0". Any example or counter-example ? Will dimensionality ...
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180 views

About thermodynamic beta

First of all, I'm not majoring this part and just finding some answer about Arrhenius rate equation: $$ v \propto \exp\left(-\frac{E_a}{kT}\right) .$$ To derive this relation, I started with ...
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4answers
200 views

Boltzmann brain vs Actual universe probability actual calculations [closed]

I have been reading lots of physics lately about how universe came into being. One idea is that universe is long gone (thermal death) and it might not exist the way I feel it and I am a sequence of ...
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588 views

$ \Delta H = C_p \Delta T $

The definition of enthalpy as a function of heat capacity and temperature change. $ \Delta H = C_p \Delta T $. Does it only apply at constant pressure? In my discussions on this board and also with ...
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40 views

What the effect of thermal diffusivity on temperature rise during friction

If we have two material in friction wich metal will produce the temperature?the metal with lower diffusivity or with higher diffusivity will be the source of temperature
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123 views

Does work done require interaction between system and surrounding?

There's no work done for a person climbing upstairs because the energy is converted to PE within system only. The person is the system. How true is the above statement?
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423 views

How does the hot cup of tea cool down? [duplicate]

I am not sure about my answer. I think that the cup of tea cools down by the following modes: Radiation between the surface of the tea and the air molecules. Conduction between the tea and the cup ...
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111 views

Pressure and Temperature in a few-body system

This question is very much related to this other one, and the introduction is the same. If we want to define intensive properties for few-body systems it is not straightforward. I am referring ...
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57 views

Niagara Falls mist

I am at Niagara Falls and noticed that the mist increased significantly at night and in the early morning. I guess it is acting like a cooling tower. Why is this happening?
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1answer
63 views

Usage of the formula Pdv for irreversible thermodynamic processes

Why do we use the formula Pdv for calculating work done in a irreversible process ? As per my knowledge , the term P indicates the pressure of the surrounding , which infinitesimally differs for the ...
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1answer
99 views

Calorimetry - Emitted Joules [closed]

How can one calculate the total amount of emitted joules from an object with a temperature that isn't constant? A great start is this formula: ...
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630 views

How do I keep the temperature constant in a Boyle's Law experiment?

I'm trying to get a head start on our lab experiment next week about Boyle's Law. The set-up is we have an air chamber can immersed in a pot of boiling water (which is kept boiling over an electric ...
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37 views

Is heat conduction impeded at interfaces between dissimilar materials?

Sound in air essentially echoes off concrete walls, rather than penetrating them, because of the difference in the material properties of air and concrete. By analogy, are there pairs of solid ...
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66 views

Zeroth law of thermodynamics and related discrepancy?

Consider the case: Assume molecules to sphere and their |velocity| as an indication of their temperature. Now for head on elastic collision (i.e transfer of heat), assume the momentum is conserved ...
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88 views

Why do particles in a medium have different speeds?

If thermal conduction occurs because of particles colliding with each other and imparting kinetic energy to each other, won’t the particles of an isolated medium collide with each other until the ...
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About energy… created, destroyed?:/

Consider a dam, in that first the hydraulic energy due to gravitational force gets converted into mechanical energy by using turbine. Then those mechanical energy is converted into electrical energy ...
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specific enthalpy change during phase change

consider 1 kg of water in a sealed cylinder and piston, whic exert 1 atm pressure on the system. Also water is saturated liquid at T=100$^\circ$ C. Then we give the system heat, so part of the system ...
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82 views

What color does graphene glow when heated?

If you heat graphene hot enough, what color would it glow? Is the color within the visible range?
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49 views

Nature of system taken in thermodynamics

Why is thermodynamic system always taken as macroscopic ? What will be the changes if one considers the same as microscopic ?
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38 views

Is it true as entropy increases things become more symmetric?

Is it true that as entropy increases in a particular domain (say, the universe or a given box) so do the symmetries within this domain? Are there exceptions? Say I'm looking at a rotational symmetry. ...
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76 views

Isothermally Adding Heat

This makes absolutely no sense to me. My physics book states the following (University Physics 12th ed, Pg 650) Suppose we want to change the volume of a certain quantity of an ideal gas from 2.0 ...
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184 views

Calculate pressure with the ideal gas law or $\rho gh$?

In a container the pressure on the walls due to a gas can be calculated using the ideal gas law $\bigl(pV=NRT\bigr)$. However, for a column of water, or the pressure at earth's surface due to a ...
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141 views

How do I calculate the change in water temperature as a function of depth?

Let's say I have ground water at a depth of $3000m$ at $50^{o}C$. If I now pump this water up to the surface, the water pressure decreases from the $\pm 300 atm$ at that depth to $1 atm$ at the ...
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1answer
124 views

Will my induction hob be powerful enough? [closed]

I'm looking to buy an induction hob to heat some water and I would like to know if its going to be powerful enough. If so, can it be done in, say, 1 hour? Additionally, what power rating could I go ...
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62 views

Hot water from a faucet

Why does hot water come out of a faucet cloudy white? The cold water comes out clear, but if you turn the hot water tap on, it'll be clear until it gets hot and then turns a cloudy white colour. ...
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172 views

Gough-Joule effect in rubber band

When a stretched rubber band is heated, surprisingly, its tension will increase. What is the physics behind this?! Another thing. The Entropic spring model says, for a good specimen, that the ...
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30 views

Determining the final state of the gas in the tank

Suppose there is air of mass m1 in an insulated tank at temperature T1 and pressure P1. 0.25m1 of air is released through a valve attached to the tank. Find the final temperature, T2 and pressure ...