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5

From the original assumptions: So far, my understanding of water evaporating is the following: The higher the temperature, the higher the vapor pressure, therefore the faster water vaporizes. The rate of water boiling, assuming a constant boiling temperature, is dependent on the rate of heat transfer to the water, not the vapor pressure. At sea level, ...


4

The answer is the same reason why a glass of water left out at room temperature will evaporate. Even though most of the particles will be below the boiling point, the equilibrium one expects is not entirely in the liquid phase. The occasional particularly energetic water molecule will vaporize, just as the occasional neutral hydrogen atom will be struck by a ...


3

Toasting not only browns the surface, it dries out and cooks the interior. Any method that applies heat to the surface and waits for it to diffuse into the interior is limited by the rate of diffusion. You can speed it up by a higher surface temperature, but this leads to uneven cooking. Radiation and particles can penetrate to the interior, and can be ...


3

The answers boils down to yes, the larger the rate of of heat (assuming you can transfer it at any rate you want), the larger the vaporization rate. The rate of change in internal energy at constant volume is $U=U_0+\dot Q\Delta t$, where $\Delta U$ is the total internal energy necessary to change the phase, and $\dot Q$ is the rate of heat transfer. Thus $\...


3

As a rough estimate: we can approximate the shape of the can with a cylinder of radius $R=3,2$ cm and height $h=15,5$ cm (those are the dimensions of a Cola can). Its total area can be found by using $$A_T=A_L+2A_B= 2\pi R h + 2\pi R^2$$ which gives us $A_T$=$375,8$ cm$^2$. Assuming that water vapor condensation forms a 1 mm thick, continuous sheet of ...


3

The noise from a fan is mostly the vibrations caused by the fan motor, and the rush of air past the fan blades. You can buy a quieter fan. It will cost more. Some new fans have no moving parts, no blades : http://electronics.howstuffworks.com/gadgets/home/dyson-bladeless-fan.htm The obvious easy way to create an air flow (cross-breeze) without creating ...


3

Your intuition that the same amount of fluid goes down and then up by the same amount is incomplete, you are forgetting what happens inside the fluid. It is easier to see using solid blocks as in the figure below: Here you can see that the effect of moving block 1 down is to shift block 2 to the right, and moving block 3 back up the same amount that ...


3

For a candle flame, following processes occur. 1. heat transfer (from flame to surrounding and to candle) 2. material transfer (wax vapor diffused outwards and oxygen diffused inwards) 3. heat generation (chemical reaction at stoichiometric mixture location) with gravity, the above will shift due to free convection flow. This will accelerate heat transfer, ...


3

I would like to answer with the words of L.D. Landau, from his book Statistical Physics (first edition $1958$):


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So far there have been quite a few insightful answers about statistical mechanical entropy, but so far the only mention of thermodynamic entropy has been made by CuriousOne in the comments, so I thought it would be useful to give a short general reminder about the subtle difference between the notion of entropy in thermodynamics and the formulas that come up ...


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Is this taken to be an additional (and apparently implicit) assumption? You are correct. Take two arbitrary points $A,B$ on the $PV$ (or any other) plane, and draw an arbitrary curve connecting them: you have just defined a reversible transformation connecting $A$ and $B$. This is because every point in the $PV$ (or any other) plane represents an ...


3

Entropy Demystified (The Second Law Reduced to Plain Common Sense) by Arieh Ben-Naim. Authored discussed not only the thermodynamics origin of entropy but also the same notion in the context of information theory developed by Claude Shannon.


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We have reached temperature as low as 0.00000001K in the lab and as high as millions of degrees in a nuclear bomb. We achieve such low temperatures by using different techniques. Laser cooling is one of them. In laser cooling, where we fire photons in a certain direction which are accepted and reemitted by atoms in such a way that they retain a component of ...


3

First get data lined up. It seems the container is not small :) volume of water: $4.80\times 10^{-4}~m^3$ heat transfer surface area (ignore wood supporting face): $0.038m^2$ mass of water: $0.48~kg$ heat capacity of water is 4.2kJ/kg-K calculate how much heat required for the water to reach room temperature. $$\bigtriangleup Q=m c (27-10)= 34.3kJ$$ ...


3

Yes. An equivalent way of saying this is that if an ice cube (or iceberg...) melts, the water level remains unchanged. (I.e.: the melted iceberg exactly fits in the 'hole' it creates underwater.) To see this, think of what is holding the ice up: it's buoyancy, which is the upward force due to the pressure of the surrounding water. This force is directly ...


2

To be honest, I believe this question is not really settled, or at least that there is not yet a consensus in the scientific community about what the answer is. My understanding of the relation is, I think, slightly different than knzhou, rob, or CuriousOne. My understanding is that thermodynamic entropy can be thought of as a particular application of ...


2

Water evaporates if it has a higher temperature and or if the humidity of the air isn't at 100%. This is a nonlinear process as the vapour pressure of water is nonlinear with temperature and the rate of evaporation is linear with partial pressure difference (the partial pressure in the water is equal to the vapour pressure). The evaporation reduces the ...


2

Work is always force times displacement in the direction of the force. The only place where the gas is doing work is at the bottom surface that is moving downward. The force it is exerting there is $PA$, where $P$ is the gas pressure and $A$ is the cross sectional area of the tube. If the lower surface moves downward a differential distance dx, the work ...


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This is the purpose of the Legendre transform, which lies at the core of hamiltonian mechanics. You have a function $E(V,S)$, which is convex for certain interval of $V$, and want to find $E'(P,S)$, where $P \equiv -\left.\frac{\partial E}{\partial V}\right|_S$. This function is given by the Legendre transform of $E$: $$E'(P,S) = PV + E(V,S)$$ for the ...


2

Because, dissipative forces convert some of the work to heat. If we want to have a reversible process we must be able to return system and its environment back to their initial states without any change in universe. For this purpose, we must extract heat from environment and convert whole of that to work and it is impossible due to the second law of ...


2

I will address your question on how the fan actually works and cools you. @sammy gerbil answered the other part about the noise. I can only add that you probably confuse the fan noise with the whistling in the ears when the wind is strong. Fan creates a flow of air — i.e., increases the speed of the particles in particular direction. Naively, this would ...


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Your intuition is correct: even though $N_2$ can never exceed $N_1$ as $T \to \infty$, something has to happen if we keep putting in more energy. What happens is that the temperature "overflows" and goes to $-\infty$. It then increases as we put more energy in, finally reaching $-0$ when $N_1 = 0$. The reason this looks unnatural is because temperature $T$ ...


2

The derivation by Pols is correct. Ryden makes the strange decision to plug the relativistic rest energy $\varepsilon = \rho c^2$ into the classical ideal gas law. Surely it makes more sense to define a classical kinetic energy $$ u = \frac{1}{2}\rho\langle v^2\rangle $$ so that $$ P = \frac{2kTu}{\mu\langle v^2\rangle} = \frac{2}{3}u. $$


2

My answer is based on our everyday experience. The simple answer is no. Suppose you have a hot pan, now put a drop of water over it and you will see that it will sustain for a while. This is because the steam makes a insulating layer between the pan and water drop. This phenomena is always present which (may not be the only reason) is one of the reasons ...


2

If water in some volume $V$ becomes gas (the attraction between water molecules is switched off instantly), then the pressure of this gas will be enormous. This is how explosive works.


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Evaporation depends on vapor pressure of environment. If vapor pressure inside the fridge is lower than saturated pressure of water at $4^\circ C$, then the water will vaporize.


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Reversible work is done by conservative forces and so doesn't depend on the path. Non-conservative forces like friction, generate irreversibility and in presence of those forces, we cannot have a reversible process. Hence, if we want to determine reversible work, we should remove all irreversibilities i.e. all non-conservative forces. In thermodynamics (and ...


2

This is a really deep question. My explanation will maybe be not so rigorous, but I hope it can help shed some light. Let's start by saying that reversible work is indeed path-dependent, so it is not a state function. Consider for example the two reversible transformations $A$ and $B$ in the picture: They both are composed by an isobaric and an ...


2

You are right that the universe formed atoms much earlier (at the temperature when photons can no longer ionize the atoms, i.e. at around $T = 150,000 K$ as you point out with your order of magnitude calculation). However, photons could still scatter off these atoms. Indeed this was quite likely considering the high density of matter in the universe. The ...


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This kind of question is more easily, quickly and reliably answered by doing an experiment, rather than a calculation. The calculation requires you to decide what are the most important mechanisms for heat loss, what formulas to use, how to take account of the shape of the container, then measure all dimensions, find the appropriate data (thermal ...



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