Entropy Definition and 999 Threads

We physicists must be careful to insure that theories begin with correct principles. One basic principle is that all quantities must be capable of being observed or measured. If a theory uses a quantity that cannot be observed, then it is not a physics theory, but a hypothesis or a...

Hey, The entropy of a black hole is S = kB (4∏GM2)/(hbar c) S=Q/T T= Q/S T = Q (hbar c)/ (4∏GM2kB) The temperature derived from hawking radiation is: T = c3 hbar/ (8 pi G M kB) Which implies Q = (1/2)M c2 Is this true? I have found online that the heat should equal...

Homework Statement Using the expression for the entropy change of an ideal gas when the volume and temperature change and TV\gamma-1 = constant, show explicitly that the change in entropy is zero for a quasi-static adiabatic expansion from state V1T1 to state V2T2.Homework Equations TV\gamma-1...

Homework Statement Every second at Niagara Falls, some 5.0 10^3 m3 of water falls a distance of 50.0 m. What is the increase in entropy per second due to the falling water? Assume that the mass of the surroundings is so great that its temperature and that of the water stay nearly constant at...

Since the entropy increase in a system is a function of time, it would seem that for different observers, rates of entropy would move differently. I am struggling a little hear with putting this into a coherent question, as I am a layman, but the jist is: both the notion of a closed system and...

Assume we have an ideal gas of N particles inside a thermally isolated cylinder of volume V, and that the cylinder is equipped with a piston that can trap the air on one side. (Assume the piston occupies no volume in the cylinder.) Initially, the piston is fully withdrawn and the gas occupies a...

I have a question about the increasing behavior of entropy. Suppose we heat a metal (Take for instance Fe) till it radiates energy and then put it in space (No medium). So the metal radiates energy in electromagnetic waves which decreases the entropy of the metal (Due to decrease in internal...

Does entropy decrease when stars are created from a dust? Does etropy decrease when water freezes?

i want a deep clarification in entropy

Hi As I understand it there are several attmepts to explain the low entropy configuration of the universe at the big bang. Is seems to me the choices on the table that I am aware of are a mutliverse as in the Caroll/Chen model . A cyclic universe as in the CCC model or some hybrid of the two...

Homework Statement Okay, so I am having difficulties with understanding the concepts around entropy, take this question: What is the total entropy change for 7 kg of ice melting from -5 C° to 5 C° in room at 5 C°. Homework Equations dS=dQ/T Q =mΔH m*c*ln(tfinal/tinitial) c_ice=2 c_water=4...

Hello guys, I just registered on this forum, so I hope you can help me with some differential entropy stuff. So I have made the attached pdf file (it's a bit messy, sorry) that demonstrates a toy version of the problem I'm trying to solve. Thing is I'm quite new to information theory, so...

I am not sure if my work is correct so I need your help to confirm it. Question: Find the change in entropy when: n mol of ideal gas (ɣ=7/5) is reversibly compressed until the pressure is three times the ideal gas at constant temperature. My answer: S=n Cv ln(T2/T1) + nR ln(V2/V1)...

Homework Statement "In the following a<b<c are finite positive constants. One mole of an ideal monoatomic gas, initially at volume Vi and temperature 1000K, expands to a final volume cVi in 3 reversible steps: (1) isothermal expansion from Vi to aVi (2) adiabatic expansion from aVi to bVi (3)...

Hi All, I tried to find entropy of liquid nitrogen in various data books, using nitrogen's CAS number, MSDS, but I was able to get the entropy of nitrogen till only 100K, not below that. Does anyone know what's the entropy of liquid nitrogen or that where can I find it? Thanks!

In ordinary QM and QFT entropy is defined using a density operator for a generalized state: S = -\text{tr}\left(\rho\,\ln\rho\right) b/c for the gravitational field we do neither know the fundamental degrees of freedom nor the Hilbert space states, a definition like \rho =...

hi i am a little bit confused about the definition of entropy that says: dS=dQ_rev/T what does this dQ_rev mean? is this definition wrong, if we are talking about irreversible processes? My idea was that when you have an irreversible process like the isobaric expansion of a gas, then...

Homework Statement From Hill's "Introduction to Statistical Thermodynamics", question 3-4 reads: (note "STR" denotes the case of most probable distribution and should be read as C*) Homework Equations The most probable distribution for a system of independent indistinguishable...

What is the variation of entropy in an isobar transformation?

The Bekenstein-Hawking entropy is expected to be, and has been shown to be in some cases, derived from counting states. However, entropy is not defined for continuous probability densities, and so I have heard it said that relative entropy (of which the mutual information is a form) is more...

I have gotten to the thermodynamics portion of my physics class, and right now I'm reading about entropy. It is taking me forever to read the chapter though because I keep pondering so many questions. - How can life be possible with the concept of entropy? Cells must organize themselves in...

I have been having a discussion with a friend and I think we have reached the limit of our knowledge, so hopefully someone on here can help! Basically the question is if a photon is emitted it will travel forever providing it never hits anything. So let's say we are close to the edge of the...

Negative Changes in Entropy?? Perhaps this is not the right forum location, but I would like to ask some of the more experienced physicists here about the notion of negative changes in entropy in the universe. According to the text I am currently reviewing by Hill, the probability that a...

Hi everybody, I have a problem with this equation: it represents the motion of a gas in a duct with friction (Fanno flow). I need to plot this function in a T-s plot, do you have any ideas? the Mach number changes along the curve... R=constant S2-S1=R*(M2-1)*log(T2/T1)$

If in theory there was a very efficient and powerfull refrigerator. Is it possible that a plant/solar panel could turn that heat into usuable energy, faster then what the frige uses up?

Homework Statement Hello, I'm studying for my final exam on statistical physics, and I found an exercise of which I think it is really easy but I'm unsure of how to do it! So now I wonder if I actually don't understand what I'm doing at all! The question is as follows: Calculate for...

Given that heat capacity is a ratio of change of energy over change of temperature, while entropy is a change of energy over absolute temperature... I was wondering if there is any basis for the idea that energy will tend to flow from media having low heat capacity to media having high heat...

Roughly speaking, I want to know how badly Shannon can fail in the one-shot setting. The standard ideas of asymptotic information theory give a precise meaning to the entropy of a given probability distribution in terms of best achievable compression with vanishing error in the limit of many...

How can you acuratley measure this? I can't see how you can give randomness a number? I've seen in some places that S = ln(the number of possible arangments) Is this true in all cases? But how can you measure the number of possible arangements?, it seems imposible to calculate the entropy for a...

On the atomic level, what is entropy? how can I visualise it? Thanks

I'm trying to understand entropy, because I have no clue what it is. Iv seen questions like this posted in other places on the web, but there seems to be a disagreement over the answer. Some people say it is the randomness and chaos of a system, and other people say it is how close it is to...

Just a quick question of something I found in my textbook but can't get how they produced it. C_p =(∂Q/∂T)_p that is the definition of heat capacity at a constant pressure p. Q is heat and T is temperature. This equation is fine and I know how to derive it. Now it is the next line which...

I would like to make a stand regarding the topic of entropy reversal. Entropy CAN in fact be reduced in a closed system, and this happens spontaneously according to the fluctuation theorem. Its been published in a well known scientific journal over a decade ago, and beforehand has been...

I measured the heat capacity of a sample under various magnetic fields. When I calculated the magnetic entropy as a function of temperature, I found the magnetic entropy measured at 0.5 Tesla is higher than that measured at 0 T. As far as I know, the magnetic field will try to allign the...

This isn't a homework question per se, but more of a coursework question. Specifically, I'm a bit at a loss as to how to go about learning a particular section of the coursework for a physical chemistry (i.e. thermochemistry) class I am taking. The section in question is that pertaining to...

Hey there. We are struggling with a problem from an old exam about statistical mechanics. I hope you can help us or give any clues. Here is the problem. Homework Statement A chamber is divided by a wall into two sections of equal volume. One section of the chamber is initially filled by an...

I suppose the meta-question is: Where do I read about this? Engineering major, not physics. Worked through Penrose's book until the tensor calculus on manifolds chapter and then sank without a trace. The popularized descriptions of quantum physics are hopelessly incomplete and as Feynman...

I'm having trouble understanding well what exactly is entropy. I know it involves an irreversible process in a closed system, but for some reason I just can't grasp well the concept. About the second Law, it involves entropy heavily so I am sure I won't understand it without understanding...

Homework Statement Mercury is a silvery liquid at room temperature. The freezing point is -38.9 degrees celcius at atmospheric pressure and the enthalpy change when the mercury metls is 2.29 kJ/mol. Wat is the entropy change of the mercury if 50.0 g of mercury freezes at these conditions? The...

what rules, energy or entropy?? any physical system goes to a state of maximum entropy or minimum energy, they don`t imply each other, by my understanding 1>third law s->0 as e->0 2>system tends to be in a state of least energy how??

We currently have a thread about logarithmic corrections to the basic black hole entropy formula. I was thinking about attempts to relate the magnitude of dark energy to the area of the cosmological horizon, and about the various analogies made between the cosmological horizon and the horizons...

Ashoke Sen has written a paper http://arxiv.org/abs/1205.0971 which uses path integrals in Euclidean gravity to compute "Logarithmic Corrections to Schwarzschild and Other Non-extremal Black Hole Entropy in Different Dimensions". Sen starts by listing several varieties of extremal black...

To show that entropy is not the same thing as disorder (what people intuitively accept as disorder) my textbook gives an example of crystallization in a supersaturated solution. And it argues that since both temprature and disorder decrease the entropy must decrease also, but it does not. Hence...

It seems that dna is constantly taking on damage - entropy. Why doesn't this damage accumulate over time? It appears that the amount of genetic damage that should accumulate would significantly outweigh the amount of ordering produced from the basic mechanisms of evolution. How is DNA ordering...

Hi guys! I'm new to the forum and had several questions about entropy. I am a bit of a physics newbie by a lot of standards but I understand a lot of it and love physics. I can understand the basics of entropy that it is (correct me if I'm wrong) basically just disorder, that it is always...

Homework Statement Two large reservoirs, H and C, are available: if H is at 900 K and C is at 300 K, what is the entropy change of the Universe if 100 J of heat are taken from H and added to C? Homework Equations ΔS=∫dQ/T ΔS_universe = ΔS_surroundings + ΔS_system The Attempt at a...

Homework Statement The following is from a book: "Terrestrial radiation, T=255 K. Emitted flux ≈ 240 W m-2. Energy density for cavity radiation ≈ 3x10-6 J m-3. Entropy for cavity radiation ≈ 1.7x10-8 J K-1 m-3." I can't understand how they have calculated the Entropy.The Attempt at a...

Hi all, Sorry if this is posted in the wrong place, I'm new here. I have a thermodynamics question. Why is the temperature change 0 in the case of a partitioned tank containing an ideal gas when the partition is removed? This seems to run counter to the idea of an aerosol spray can...

Gamma (Cp/Cv) of a gas Homework Statement An experimenter adds 980 J of heat to 1.75 mols of an ideal gas to heat it from 10.0 C to 25.0 C at constant pressure. The gas does 234 J of work during the expansion. Calculate gamma (Cp/Cv) for the gas. Homework Equations Cv=Cp-nR Gamma...