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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Work done by introducing a spin in supersposition into a Magnetic Field

A spin is created in a superposition of up and down states. A magnet is moved very slowly, towards the spin. What is the work done by the magnet. It may be helpful to imagine that the magnet is ...
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6k views

How much work is needed to compress a certain volume of gas?

I want to know the formula (and what does the symbols stand for) for how much work is needed to compress a certain volume of gas?
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183 views

Does the molten salt used at projects such as Gemasolar need to be replaced after some cycles?

The project at Gemasolar uses molten salt to store heat. This heat is then used with water to drive steam turbines. Over time does this kind of repeated heat/cold cycle make the molten salt a less ...
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384 views

How does the entropy of a system change when the amount of substance changes?

I am thinking of a closed system consisting only of an ideal gas. Suddenly, the amount of substance of the gas changes. No other property of the system shall change. How does this affect the entropy ...
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171 views

Is a low-current electrical arc harmful to humans?

I've heard that electrical flux non-destructive particle testing machines are considered safe because they use less than 2 amps. I have seen an arc created between two objects do considerable damage, ...
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84 views

System moves away from equilibrium $\rightarrow$ it has energy added?

Suppose there is an isolated system $A$ at time $(-\infty, t_1)$, whose entropy is $S=S_{max}$, i.e. it is at thermodynamical equilibrium. Between moments $[t_1, t_2)$ the isolation is violated and ...
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366 views

Energy versus free-energy diagram

Energy versus free energy diagram. I haven't been able to find an adequate definition of these two terms in relation to each other. Could someone point me in the right direction, please? From Borrell ...
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642 views

Temperature change effected by electric heater [closed]

A 40-gallon electric water heater has a 10kW heating element. What will the water temperature be after 15 min of heating if the start temp is 50F degrees. There must be an equation. I can't find it ...
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823 views

Calculate time to heat my swimming pool

I have a swimming pool of 5300Liters. I have a heating element from a washing machine taking 1min17s to heat a bucket (10L) of water from 22 degrees to 30 degrees celcius. the water in my pool is 19 ...
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579 views

Heat & thermodynamics question based on heat loss [closed]

A Sphere A is placed on a smooth table.Another sphere B is suspended as shown in the figure.Both the spheres are identical in all respects.Equal quantity of heat is supplied to both spheres.All ...
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46 views

'Mechanical equilibrium does not necessarily mean that the pressure is same at all points of the system' - why?

If there are variations in pressure or elastic stress within the system,parts of the system may move, or expand or contract. Eventually these motions,expansions or contractions will cease, and when ...
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44 views

Does turning a light off save electricity in a room heated by an electric space heater?

Suppose I've got a basement that kept heated to 20 degrees Celsius using an electric space heater with thermostat. There are no windows in this basement (light is not escaping the room in any ...
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23 views

Explanation for Homogeneous Nucleation Temperature?

What is homogeneous nucleation temperature (for water this is listed as -42C); is it simply the lowest experimental temperature you can go before supercooled liquid turns into solid, or is it that ...
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24 views

Why does the equation for effectiveness of heat exchangers have $C_{\text{min}}$ in the denominator?

For an ideal heat exchanger of infinite length, $$ Q_{max}=m_{h}C_{h}\left[T_{h,i}-T_{o}\right]=m_{c}C_{c}\left[T_{o}-T_{c,i}\right] $$ \begin{eqnarray*} m_{h}C_{h}T_{h,i}+m_{c}C_{c}T_{c,i} & ...
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17 views

Is it possible to cool magnetic dipoles with a magnetic static field?

Suppose you have a bath of magnetic dipoles, with a common mean rotational kinetic energy. Now you apply a very strong magnetic field so that the dipoles align with the field, thus "losing" their ...
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35 views

compressibility of cold atoms in optical lattices

The compressibility of cold bosons in an optical lattice is defined as $\kappa = \frac{\partial \langle n\rangle}{\partial \mu}$, where $\langle n\rangle$ is the density and $\mu$ is the chemical ...
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20 views

Estimating the effect of radiant barrier on the radiant and conductive heat transfer through a metal roof

The basic question is -- Will a radiant reflective coating be more effective applied to the upper surface or the lower surface of a metal? Case 1: Imagine a metal roof subject to solar heating. The ...
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39 views

How can entropic effects be prevalent at low temperatures?

I read in a book that at low temperature the hydrophobic effect (for example) is entropic but at high temperatures it is enthalpic. I thought that entropy should decrease at very low temperatures. ...
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63 views

Helmholtz free energy from a relation for entropy

The Legendre transformation defines the helmholtz free energy (at least according to my lectures) as: $F(T,V,N)=E-TS$ It also says to start with $E(S,V,N)$ and $T=\frac{\partial{E}}{\partial{S}}$ ...
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40 views

Temperature change: boiling pasta in a lot of water or a little

SeriousEats gives a not-very-scientific representation of what looks like a thermodynamics calculation: Want to hear something even more interesting? Folks will occasionally say that "using a ...
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32 views

Showing the thermal expansion coefficient is the sum of the linear expansion coefficients

Given that the thermal expansion coefficient is defined as: $$ \beta=\frac{\frac{\Delta V}{V}}{\Delta T} $$ and the linear thermal expansion coefficient is defined as: $$ \alpha = \frac{\frac{\Delta ...
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59 views

If you dig a deep tunnel, will the rock sublimate?

If a tunnel is dug deep inside the crust (but before reaching places where the rock is liquid), how will the enormous downwards pressure manifest itself? Will the difference in pressure ...
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53 views

Dark Matter as possible an explanation for Coronal Heating

It's my understanding that the mechanism behind Coronal Heating - why the Corona is so much hotter (> 1,000,000 K) than the surface of the Sun (6,000 K), and the mechanism by which the energy gets ...
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57 views

Efficiency of reversible engines

I'm a little confused about something. All reversible engines have the same efficiency, or one could drive the other to move more heat in the reverse direction. Also, no engine has an efficiency ...
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59 views

How to define the thermodynamic temperature

I've been reading derivations of the thermodynamic temperature scale. I'm assuming these are using Kelvin's method. I follow the math and the conclusion of the argument, but I don't understand how it ...
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97 views

Can statistical mechanics explain the second law completely? [duplicate]

Statistical mechanics is restricted to the postulate of the equal a priori probability, but this postulate does not need to be considered for thermodynamics, so the valid ranges of statistical ...
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50 views

Thermal Velocity

What is thermal velocity? What is it's physical significance? Wikipedia says: The thermal velocity or thermal speed is a typical velocity of the thermal motion of particles which make up a gas, ...
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34 views

Macro-Level Explanation of Fluid Heat Transfer

Here's something I've been struggling with for a while. Say you have a hot fluid and cold surface (or the reverse, so long as there is a temperature difference) where the fluid flows over the ...
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43 views

Energy comparison, evaporate water vs compress air, same mass

I would like to compare the energy requirements of the 2 following tasks: Total energy to evaporate 1 litre of water at normal atmospheric pressure at normal temperature? Total energy to compress ...
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68 views

conducting heat to infinity

I am modeling a situation in which an object that is a small object that is spherical in shape is receiving heat at a constant rate and then conducting it away into a medium that can be model as ...
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31 views

How many state configurations are possible for $N$ particles in completely different states?

How many state configurations are possible for $N$ particles in completely different states? I cannot remember if the total number of state configurations for $N$ particles in completely different ...
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3answers
110 views

Does the entropy of an adiabatically isolated system stays the same after we decrease/increase the pressure?

Even if the system is isolated and there is no heat exchange with surroundings, shouldn't the decrease/increase of pressure result in increase/decrease of entropy? Does this property of an ...
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83 views

Gibbs equation and third law of thermodynamics

I have seen a discussion of what would happen for an ideal gas expands irreversibly and adiabatically until absolute zero degree K. The entropy change is like that: Δs=Cv ln(T2/T1)+R ln(V2/V1) It is ...
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52 views

Does stew lose more liquid if stirred as it cools?

Suppose I cook a stew or soup and then take it off of the stove and leave it uncovered to cool. Of course, it will cool faster if I stir it (more surface area), but it will, eventually, cool to room ...
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61 views

Electromagnetic radiation and health issue

A lots of article even wiki tells that Cell phone radiation is very dangerous for health. Some people tell that it can be reason for brain cancer. A article Mobile phone subsides man’s sperms! ...
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19 views

Perfect Ideal Gas Modelization of Air

I'm solving a Thermodynamic problem. I have Air at temperature of 293.15 K, and pressure of 20 MPa. I would understand if is possible to consider this an Ideal Gas or not (and if is possible which are ...
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34 views

Thermodynamic potentials and approach to equilibrium

I have seen some material which tries to show that when approaching equilibrium upon different constraints, the changes in some thermodynamic potential is always positive or negative (for example, ...
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166 views

Heat equation : boundary conditions?

Say we have a bar centered at $x=0$, that is heated. We have the 1D Heat equation which we can solve to find a parabolic temperature profile : $$\kappa \frac{d^2 T}{d x^2}=-\frac{Q}{L S}$$ with ...
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29 views

Does a surface in front of a radiator (not in contact) have a significant effect on the room's temperature or heating rate?

Does a surface in front of a radiator (not in contact) have a significant effect on the room's temperature or heating rate? Some time ago I had a discussion about it, and despite none of us knowing ...
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36 views

Can the thermal energy in an object be aligned, creating a thermal jerk?

Thermal energy is related to the speed at which atoms vibrate, therefor thermal energy is a form of motion. In a stationary object, all of these vibrating atoms 'impact' each other in such a way that ...
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71 views

Steady state average of physical quantities

Consider the following Hamiltonian: $$ H = \sum_n \left[\dfrac{p_n^2}{2m_n} + U(x_l) + V(x_{l+1} - x_l) \right], $$ that corresponds to a 1-D system of particles with nearest-neighbor interactions ...
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56 views

How can I calculate the speed at which water evaporates when held at 100 degrees Celsius?

If I have a mixture of some higher bp solvents and water, and I heat it to 100 degrees celcius so that the water in the mixture begins to boil, how can I calculate the rate at which water leaves the ...
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44 views

Chemical potential in terms of temperature and pressure

For part (a), I know how to take the partial derivatives of S to get chemical potential, pressure. But there seems that I still need one equation to correctly express chemical potential in terms of ...
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40 views

Thermal Physics, Specific Question [closed]

Question: The melting point of copper is 1080 degrees Celsius and its heat of fusion is 200 kJ/kg. If a copper coin at this temperature is completely melted by the absorption of 2000 J of heat, what ...
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106 views

Do reversible processes exist in Nature?

Classical thermodynamics always discusses entropy in the light of reversible processes, and it lies at the heart of the definition of entropy. But do these reversible processes exist in Nature, or are ...
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102 views

How hot does the upstairs need to be before it will heat the basement through convection?

During the winter we keep the basement door closed so that the cold air from upstairs won't flow into the basement. Then we heat the basement and the upstairs gets heated partially by conduction ...
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107 views

Information or Matter or Energy

Which one is the most fundamental of the universe? What it is made of? Physicists are searching for unique and fundamental form. The question is , information is more fundamental than energy ? ...
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201 views

What does 1/k represent regarding Newtons Law of Cooling?

What does 1/k represent regarding Newtons Law of Cooling? I know k represents the cooling constant. I think the inverse of k is the time taken for the liquid to cool from its maximum temperture to ...
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2answers
179 views

Isobaric expansion work, W = p(V2-V1) [closed]

Isobaric process, so $W = p\Delta V$ according to my book. We have 10 kg of saturated steam at $x = 0.9$, P = 200 kPa. We add work at a rate of $700 W$ and we're interested in the time it takes. We ...
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53 views

Thermodynamic entropy vs. quantum mechanical entropy

Is there a fundamental difference in the definition of entropy when considering the classical thermodynamic picture vs. the quantum mechanical picture, or are they both fundamentally equivalent?