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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$\Delta T$, temperature units. How to use fahrenheit in this formula

To calculate the power in a fluid with a flow, the following formula is applied: $$P = \Delta T \rho c_p \times flow$$ $\Delta T$ can be entered as both Kelvin and Celsius. But what if I want to use ...
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56 views

An isolated Earth

It is known the fact that there is no way to extract energy (in any form) from any system without introducing some energy. The Earth for example, gets energy from the Sun, from nuclear fusion of ...
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95 views

Function describing an adiabatic process

I understand that an isothermic process, plotted on a PV diagram, can be described by a rectangular hyperbola. However, now I am wondering, what about an adiabatic process, what function best ...
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156 views

General Thermodynamic equation of state

I heard my professor saying that the equation $$ PV = \frac{2}{3}U $$ is valid for any non-relativistic gas, be it Ideal or Real gas(includes quantum ideal gases). Is this true, If it is how can we ...
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650 views

Is energy released during change of state?

When a substance changes state from solid to liquid, the temperature of the substance remains the same and the heat energy from the external source is converted to potential energy within the ...
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284 views

Why does the coefficient of performance need to be calculated with $W + Q$?

How much work must a heat pump with a COP of 2.50 do in order to extract 1.00 MJ of thermal energy from the outdoors (the cold reservoir)? The first formula that came into my mind after reading ...
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569 views

Temperature rate of change inside a cylinder

I was wondering about this today, mainly for baking a cylindrical cake. Say you have a solid cylinder which is at temperature T0 inside. Say you then move the ...
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299 views

Molar heat capacity of gas defined by relation $p=kV$

we have this problem where relation between Pressure($p$) , Volume($V$) is defined by relation $$p=kV$$ where $k$ is a constant and we have to find the molar heat capacity of the gas. Note:Ideal gas ...
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82 views

Microwaves and state of matter

Does the heating efficiency of a microwave oven depend on the state of matter that it heats? If yes, how?
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520 views

Why does the specific thrust of an ideal turbojet drop with increasing compressor pressure ratio?

As the pressure ratio increases in an ideal turbojet (fixed flight Mach number), the specific thrust, $\frac{F}{\dot{m_{air}}}$ rises, reaches a peak for small pressure ratios and then starts to ...
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154 views

Max temperature that can be obtained from radiation source when nonlinear interaction with matter is important?

Using a black body radiation as furnace it is usually said that the max achievable $T$ is limited to the T of the source. So a source of 3000K can not be used to heat a body above 3000K. A long ...
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970 views

Why do larger planets cool more slowly than smaller ones?

I learned it during my environment class. My professor introduced the concept--- ratio of surface area and volume. The numerator has connections with the radiative loss, while the denominator is ...
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659 views

What is the importance of state functions in physics?

I'm currently reading about the Carnot cycle and its significance on the formulation of entropy (because I want to try to understand the concept better), but I can't seem to answer the following ...
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4k views

Definition of “intensive” and “extensive” properties

Today I was asked what does it mean for a physical property of a system to be intensive. My first answer, loosely speaking, was: "It is a property that is local." I was specifically thinking ...
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485 views

What is meant by boiling off electrons in a heater coil?

In my electricity and magnetism course, we used a Thompson tube to produce an electron beam. There is a heating element at the back of the tube and the lab manual claims that "electrons are boiled ...
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98 views

Bug in linear thermal expansion, $L_0$ must be $0$

Assume we change the temperature of an object with negligible size in $2^{nd}$ and $3^{rd}$ dimensions from $T_0$ to $T_1$ to $T_2$, with all of them pairwise different. We choose a substance with ...
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1k views

Must a reversible engine be a carnot engine?

I have this homework question: "Show that any reversible engine operating between T1 and T2 is a carnot engine." I think I have a solution, but it feels very hand-wavy. We know that any process that ...
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185 views

What's the relationship between the energy density of a black-body and its radiant exitance?

Through a bit calculation we can derive that in a cavity, the energy density $$u(f,T)=\overline{E(f)}\times G(f)=\frac{8\pi h}{c^3}\frac{f^3}{e^{h\nu /kT}-1}$$ If we take the integral over all ...
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341 views

How does heating cause motion?

W.R.T. Newton's laws a force is required to change the state of rest of a body. Then how does heating cause a particular object's atoms and molecules to wiggle ? What is the force being applied when ...
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650 views

Difference between a quantum process and a thermal process?

I was reading an article online pertaining to quantum mechanics and I stumbled across these few sentences. A look at the corresponding energy regimes shows (Beck and Eccles 1992) that quantum ...
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220 views

How can I determine (measure?) if spraying my A/C condenser with water will make it operate more efficiently?

My brother had an idea for a DIY project and I am curious if the science works out well enough to try it. The idea is to collect rainwater then mist it onto the air conditioners condenser coils (the ...
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217 views

Dimensional analysis of magnetic energy: dimensions of µ0 and H

When calculating the energy difference between the normal and the superconducting state in a superconductor at zero magnetic field, the result is as follows: Now I'm quite confident of this result, ...
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799 views

How is the distribution probability in the canonical ensemble derived?

I'm confused by the derivation of the canonical ensemble, namely the origin of the probability density, that is the Boltzmann factor. Here's what I have: We have a system of particles with ...
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1k views

Minimization of energy and maximization of entropy

Are maximization of entropy and minimization of energy equivalent? Or are they contrary? Why should the thermodynamic potentials such as $G$, $A$, etc, be minimum at equilibrium? I am confused. ...
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595 views

What is tricritical point?

Critical point is the transition temperature of a second order phase transition. But what does tricritical point mean? WIki says that a tricritical point is a point in the phase diagram of a system at ...
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3k views

How is it possible to equate the internal energy at constant volume with the internal energy of an adiabatic process?

I hope my question makes sense. My problem is that, I have read through numerous textbooks that $$nCdT = -PdV$$ (where $NC$ is constant volume) when deriving the relationship between $T$ and $V$ for ...
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60 views

What is the coefficient $\mu_\text{air}$?

I am answering some exercises in thermodynamics, and I am still in trouble with some values and constants. In the exercise, it is given: $\mu_\text{air}=1.8\cdot10^{-5}~\text{kg/m s}$. What for is ...
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240 views

What is the term for heat generation by a flowing fluid?

I would like to know more about the heat distribution over time in a flowing liquid. To this end, I consider the Navier-Stokes equation (where the coefficients may be temperature dependent) and the ...
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3k views

How does a thermal temperature gun work?

I once worked as a kitchen porter over a winter season. We had fun with thermal temperature guns (like these) which I learned can be used for measuring the temperature of something a reasonable ...
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2k views

What's the physical difference between a convective heater and an infrared heater?

Could someone please explain why there are 2 types of space heaters-- one that is convective and one that is infrared? Why does the first one not radiate and why does the second one not heat the air? ...
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231 views

Calculating outside temperature based on indoor measurements

If I take three consecutive measurements $T_0$, $T_1$, $T_2$ at equal intervals, I can end up with two (Newton’s law of cooling) equations where the $e^{-kt}$ term is the same. $$T_{n+1} = ...
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195 views

Why can we not reduce the size of a system below the correlation length without qualitatively changing its properties?

This question is posed in the context of thermodynamics/statistical mechanics. Suppose we define the correlation length as the $\xi$ in the exponential factor $e^{-r/\xi}$ that appears in the ...
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334 views

An explanation for the Landauer's principle

Has anyone understood the Landauer's principle? What is the current status? In specific, is there a theoretical derivation of the Landauer's Principle?(not the heuristic one based on Salizard's ...
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1k views

Does the volume of a thermodynamic system always have to change for it to do work?

Does the volume of a thermodynamic system always have to change for it to do work? If yes,could you explain why? And if no, could you provide the example of a system, where it is not neccesary.
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Adiabatic expansion [closed]

I'll start off by saying this is homework, but I ask because I don't understand how the math should work (I don't just want an answer, I'd like an explanation if possible). I understand if this is ...
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11k views

What makes water boil?

Basically how boiling takes place? Also like to know... What makes boiling point alter at various altitudes? Why bubbles rise through boiling water?
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219 views

Double internal energy, how much will the entropy change?

Approaching the following question Imagine we have a collection of $N = 100$ simple harmonic oscillators. The total internal energy is $U = q \epsilon$ where $q$ is the number of energy ...
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691 views

Calculating temperature of water in the freezer

Assuming water volume ($V$), initial water temperature ($T_0$) and environment temperature ($T_e$) are known, what is the easiest way to calculate temperature of water in given time ($T$)? For the ...
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2k views

Thermal Energy from Friction on a Rope

Question: A capstan is a rotating drum or cylinder over which a rope or cord slides to provide a great amplification of the rope's tension while keeping both ends free. Since the added tension in the ...
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2answers
2k views

What is the physical or mathematical meaning of the Gibbs-Duhem equation?

The Gibbs-Duhem equation states $$0~=~SdT-VdP+\sum(N_i d\mu_i),$$ where $\mu$ is the chemical potential. Does it have any mathematical (about intensive parameters) or physical meaning?
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841 views

Heat absorbed by a room

How can one calculate the amount of heat absorbed inside a room in a single day using the temperature readings of the day? If the temperature has to be reduced from 30C to 20C how much heat should be ...
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In the Niagara Falls, which factors prevent rise of T H2O falling a certain height?

I need some ideas on a problem. The first part says: Whats the posible rise in the temperature of the water falling 49.4 m in the Niagara Falls? That one was easy, with answer 0.112 Kelvin. ($\Delta ...
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1k views

Finding coefficients of volumetric expandtion from a know coefficient of linear expandtion

Starting from a homework problem: An aluminum cup of $100 cm^3$ capacity is completely filled with glycerin at $22°C$. How much glycerin, if any, will spill out of the cup if the temperature ...
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3k views

When a gas expands against an external pressure of 0, must the stopper on the cylinder be massless?

Basically, I need to conceptually understand why the work a gas does is the integral $\int p_\mathrm{external}dv$ and is 0 when pressure external is 0. I understand why $\mathrm{d}w = - ...
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630 views

Given two boiling temperatures and pressures, how can I find the latent heat?

I am given the fact that at a certain pressure a liquid boils at a corresponding temperature, at a different pressure it boils at a different temperature, and then I am asked to find the latent heat ...
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148 views

How does the period of a temperature fluctuation affect the depth to which the ground freezes?

On account of the annual fluctuation of temperature the ground at the town of Ν freezes to a depth of 2 metres. To what depth would it freeze on account of a daily fluctuation of the same amplitude? ...
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124 views

Is there a timeline in urban area night temperature?

Fact: We all know that during the day concrete absorbs heat and releases it during the night, making urban areas hotter than rural areas. I observed that after sunset the ambient temperature is going ...
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1k views

Work for constant volume compression by adding moles of gas

I often see the expression $W = V \Delta P$ for the work of a constant volume compression where there are a fixed number of moles and the compression is caused by heating. Is this the work equation ...
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221 views

Cooling via the quantum vacuum?

Suppose you had an isolated cloud of gas at a low temperature in a vacuum with no external sources of radiation (e.g. no CMB). The gas would clearly cool via the emission of low-energy photons. But ...