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Question: <p>Concerning combustion of fuel droplets:</p>
<p>Why is the mass fraction of fuel on a fuel droplet surface slightly less than one?</p>
<p>It is known that the temperature is below the boiling point at the fuel droplet surface, so there is no evaporation at the surface and therefore my intuition tell me th... | https://physics.stackexchange.com/questions/66766/mass-fraction-of-fuel-on-a-fuel-droplet-surface |
Question: <p>I'm looking for a source where I can find the temperature coefficient of resistivity at different temperatures for pure metals. Tables are everywhere for 20$\,^{\circ}$C, but I'm having difficulties finding data for other temperatures.</p>
<p>One resource I looked at (<a href="http://www.physicsforums.co... | https://physics.stackexchange.com/questions/67977/is-there-a-source-that-provides-data-for-the-temperature-coefficient-of-resistiv |
Question: <p>In the demonstration of the Clausius theorem in classical thermodynamics my book uses the fact that $Q_{net}\le0$ is negative in a cyclic monotherm (meaning with one heat reservoir) transformation. This fact, however, left me a bit uneasy. Taking, as usual, a Carnot cycle as an example, and calling the adi... | https://physics.stackexchange.com/questions/69462/monotherm-cycle-negative-q-net |
Question: <p>Since a <a href="http://en.wikipedia.org/wiki/Pulse_tube_refrigerator" rel="nofollow">pulse tube cooler</a> is basically a Stirling engine without moving parts running "in reverse", does that imply that when I keep the cold end at ambient temperature and apply heat to the hot end, I get pressure oscillatio... | https://physics.stackexchange.com/questions/71000/can-i-run-a-pulse-tube-cooler-in-reverse-to-generate-pressure-oscillations |
Question: <p>In the compression stroke of a petrol engine, the mixture is compressed by the upward movement of the piston. From where does the piston get energy to compress the mixture?</p>
<p>Similarly, in the exhaust stroke, the piston again moves upward to expel the gases. Where does the piston get energy from?</p>... | https://physics.stackexchange.com/questions/72574/energy-provided-to-piston-in-compression-and-exhaust-stroke |
Question: <p>I know boiling point at vacuum is far below the room temperature. But I still wondering if the humidity reaches the saturated humidity (100% relative humidity), will the vapor condense to liquid, although it is probably going to evaporate again soon?</p>
Answer: <p>While dmckee points out your question is... | https://physics.stackexchange.com/questions/74490/can-water-exist-as-liquid-in-a-vacuum-chamber-at-room-temperature |
Question: <p>Why do water of water based liquids like sweat cool objects? The most clear example I have is the sweat on the skin. I learned that it absorbed heat because it evaporates, but this is something strange. I also read that by putting a little water on a can under the sun will cool the inside of the can, for t... | https://physics.stackexchange.com/questions/76367/water-coolso-object-by-heat-absorption |
Question: <p>Why does the stale smell disappears in a crowded room if you cool it via air-condition ? What's the physics ?</p>
Answer: <p>It doesn't have anything to do with thermodynamics – the stale smell is due to certain molecules or mould spores floating in the air. Putting fresh air into the room, and removing t... | https://physics.stackexchange.com/questions/78620/thermodynamics-in-a-closed-room-why-does-the-stale-smell-depend-on-temperature |
Question: <p>I know that molecules in ideal gas can move freely, and molecules in crystal are bonded to some specific location. But can I describe this in a more quantitative way? Do gas molecules have more degrees of freedom?</p>
Answer: <p>Yes, by examining the statistical distribution of distances between molecules... | https://physics.stackexchange.com/questions/82388/how-can-you-tell-between-gas-liquid-and-crystal-in-a-microscopic-way |
Question: <p>I'm not sure if this question belongs here, because I'm asking a question about experimental data rather than theoretic formula.</p>
<p>Anyway, I'm trying to figure out the time-temperature relation of the (hot) water in an ordinary sports bottle. Assume the bottle is full with 500mL of water in it. Do yo... | https://physics.stackexchange.com/questions/83956/experimental-heat-equation-for-a-bottle-of-water |
Question: <p>The concept of work is clear from mechanics, where $dW=F\cdot dx$, leading to $dW=PdV$. Also different forms of energy are defined in mechanics, e.g., $E=\frac{1}{2}m v^2$, etc. How are the energy and heat defined and measured in thermodynamics?</p>
<p>Because once we define them independently, we can sta... | https://physics.stackexchange.com/questions/87222/definition-and-measurment-of-energy-and-heat-in-thermodynamics |
Question: <p>As far as I understand it, the first principle of thermodynamics is a mere definition of the quantity “Heat”: $$\text d Q: = \text d L + \text d U.$$
This is somewhat the point of view taken in Fermi's introductory book "Thermodynamics": </p>
<blockquote>
<p>[...] $$\Delta U + L=0$$If the system is not ... | https://physics.stackexchange.com/questions/87080/what-are-the-experimental-observations-behind-the-first-principle-of-thermodynam |
Question: <p>I have a problem where, basically, in part (a) I correctly found a fundamental equation $$TdS = dE - 2\sigma l dx$$</p>
<p>Then the problem goes on to say that the only parameters of interest are $x$ and $T$, so I would assume we can write the relation $$dS =
\frac{\partial S}{\partial x} dx + \frac{\par... | https://physics.stackexchange.com/questions/88605/maxwell-relations-confused-on-how-the-solution-got-to-this-answer |
Question: <p>Australia's history has been littered with the problem of how to manage safety in bushfires. The local fire authority recommend consideration be given to preparing a bushfire management plan, deciding whether to stay and defend, or leave early.</p>
<p>A back- up plan is also suggested, which may include t... | https://physics.stackexchange.com/questions/87662/thermodynamics-and-wall-insulation |
Question: <ol>
<li><p>Please describe how a <a href="http://en.wikipedia.org/wiki/Vacuum_flask" rel="nofollow">vacuum flask/thermos</a> works. </p></li>
<li><p>How does the vacuum prevent convection/conduction/radiation? </p></li>
<li><p>How does the lid with the curvy lines prevent either of the aforementioned heat tr... | https://physics.stackexchange.com/questions/89411/please-describe-how-a-vacuum-flask-thermos-works |
Question: <p>If 700 J of work is applied onto a gas, and therefore the gas contracted 0.005 m^3 (from 0.01m^3), and the temperature stayed at a constant rate of 300 kelvin, then how come when pressure is added to the system (Not by adding more molecules, but instead by increasing the kinetic energy of the molecules by ... | https://physics.stackexchange.com/questions/89902/what-is-the-difference-between-heat-and-work |
Question: <p>I have the heat balance equation for a cooling case in the form:</p>
<p>$$\frac{dU(T(t))}{dt}=-J$$</p>
<p>with</p>
<ul>
<li>$U$: energy (J)</li>
<li>$T$: temperature (K)</li>
<li>$t$: time (s)</li>
<li>$J$: heat flux leaving the system (W)</li>
</ul>
<p>I have $U$ from experimental data; $U$ is a funct... | https://physics.stackexchange.com/questions/90683/heat-balance-how-to-obtain-tt-with-energy-in-the-form-utt |
Question: <p>In the steam bath at the health club, why is the "steam" thicker first thing in the morning before it has been used all day and the walls are "hotter"?</p>
Answer: <p>When you say it's "thicker" in the morning, do you mean it seems more foggy/cloudy when the bath is first turned on? I suspect someone more... | https://physics.stackexchange.com/questions/90797/steam-bath-physics |
Question: <p>I'm looking at <a href="http://books.google.ca/books?id=RN4_jLbVO3YC&pg=PA50&dq=Stirling+auto+engine+a+lot+of+progress,+but+Spirit&redir_esc=y#v=onepage&q&f=true" rel="nofollow">this</a> Stirling engine, which I believe is a variation of an alpha type. It was developed by Nasa back in t... | https://physics.stackexchange.com/questions/92642/how-does-this-stirling-engine-work |
Question: <p>I am studying thermocouples. In a text book, the author said that, the electromotive force can be written as</p>
<p>$$ E= \alpha \theta + \beta \theta^2 \tag{1}$$</p>
<p>where $\alpha$ and $\beta$ are constants and the thermocouple is connected at $0 \;\mathrm{°C}$ on one end and at $100 \;\mathrm{°C}$ ... | https://physics.stackexchange.com/questions/92045/thermo-couple-eelectroomotive-force |
Question: <p>A Stirling engine evidently functions by heating and cooling air, thus making the piston move up and down. What if the heated side of the cylinder were shaped as a sort of cone with a gentle slope, cut off before a point forms (I guess it would look like a trapezoid from the direct side), so that the surfa... | https://physics.stackexchange.com/questions/92273/would-a-cone-shaped-stirling-engine-work |
Question: <p>Lets say you have 1 liter of hydrogen in a sealed container, at 100 psi. If 50 cm^2 of the containers surface area is heated to a 1000 degree Celsius, will the psi increase over time? What would be the formula to figure this out in terms of the amount of pressure added and the time frame it takes? No need ... | https://physics.stackexchange.com/questions/93072/does-heat-increase-the-volume-of-a-gas-and-in-turn-its-pressure |
Question: <p>In my text book, it is given : </p>
<blockquote>
<p>One calorie is defined as the amount of heat required to raise the temperature of water from 14.5 °C to 15.5 °C.</p>
</blockquote>
<p>I found out in wikipedia that this is actually the definition of 15 °C calorie. </p>
<p>I want to know that as tempe... | https://physics.stackexchange.com/questions/95527/amount-of-heat-required-at-for-unit-rise-in-temperature-at-different-temperature |
Question: <p>I always get confused what exactly happens when two ideal gases mix.</p>
<p>Consider the initial situation where two gases are in a box, separated by a rigid and adiabatic wall between them. Now when the wall between them is removed, they come to equilibrium (of course assuming the process is done quasi-s... | https://physics.stackexchange.com/questions/96089/mixing-of-ideal-gas-thermodynamic-equilibrium |
Question: <p>The project at <a href="http://www.torresolenergy.com/EPORTAL_DOCS/GENERAL/SENERV2/DOC-cw4cb709fe34477/GEMASOLARPLANT.pdf" rel="nofollow">Gemasolar</a> 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 mo... | https://physics.stackexchange.com/questions/32018/does-the-molten-salt-used-at-projects-such-as-gemasolar-need-to-be-replaced-afte |
Question: <p>For a pure species, the equlibrium between liquid phase and vapour phase is given by the equality of molar Gibbs energy in both phase:</p>
<p>$$\underline{G}^l=\underline{G}^v$$</p>
<p>Where $\underline{G}$ with an underline represents molar Gibbs energy.</p>
<p>In a multicomponent system, the equilibri... | https://physics.stackexchange.com/questions/33499/multi-component-mixture-phase-equilibrium-criteria |
Question: <p>OKay my book just starts out talking about the vague definition we have for temperature and we ended up with the Zeroth law of Thermodynamics which states:</p>
<blockquote>
<p>Two systems are in thermal equilibrium if and only if they have the same
temperature.</p>
</blockquote>
<p>So does that mean,... | https://physics.stackexchange.com/questions/35898/do-i-have-the-meaning-of-the-property-temperature-correct |
Question: <p>Assume for purposes of discussion a closed container with a concentration of gas on one side and near-vacuum on the other. We could let the gas pressure equalise naturally, or we could construct a barrier with a turbine such that the gas moving from the concentrated side to the vacuum side spins the turbin... | https://physics.stackexchange.com/questions/38839/gas-pressure-equalisation-where-does-the-excess-energy-go |
Question: <p>Heating value of liquid-gas mixture was tested with primus which has gas burner. In the initial state aluminum container with lid protected from the wind has temperature of 0 celsius and in it 0,54 kg of water and 0,82 kg of ice cubes. Mixture was then heated to 100 celsius. During the heating 0,022 kg of... | https://physics.stackexchange.com/questions/39033/how-to-evaluate-heating-value-on-the-basis-on-these-data |
Question: <p>I did something very stupid tonight. I poured hot water into an polyethylene water bottle and it immediately contracted causing it to overflow and burn my hand and leg. I immediately wasted my hand and feet with cold water.</p>
<p>Now I am left with a useless bottle that resembles what you see at a modern... | https://physics.stackexchange.com/questions/38529/thermal-expansion-is-there-a-way-to-fix-my-bottle |
Question: <p>Is it true that the mass of air in normal atmospheric pressure over 1$m^2$ is 10326 $kg$?
I calculated it from pressure formula </p>
<p>$p=\frac{F}{A}$. </p>
<p>Let $m=?, A=1 m^2 and p=101300 Pa$. </p>
<p>$p=\frac{F}{A} \Leftrightarrow ...\Leftrightarrow
m= \frac{pA}{g}=\frac{101300 \cdot 1 }{9,81} = 10... | https://physics.stackexchange.com/questions/39553/is-it-true-that-the-mass-of-air-in-normal-atmospheric-pressure-over-1m2-is-10 |
Question: <p>Consider a desalination process where you enter sea water and receive fresh water and brine (or maybe pure salt).</p>
<p>How do I compute the least amount of energy per mass? I think this has something to do with the entropy of the different mixtures, mostly dependent on the salt concentration in the brin... | https://physics.stackexchange.com/questions/43955/whats-the-lower-limit-for-energy-usage-to-desalinate-water |
Question: <p>I was reading about <a href="http://it.wikipedia.org/wiki/Mulinello_di_Joule" rel="nofollow">the experiment of Joule</a> (Italian wiki page). I'm not sure how it's called in English, since there is only an Italian and French version. In any case, in the page it is stated that (my translation):</p>
<blockq... | https://physics.stackexchange.com/questions/45212/what-is-the-importance-of-joules-experiment |
Question: <p>I've produced experimental data over how the boiling point of water varies with pressure and temperature and plotted this in a PT graph. I would like to verify my results using theory. The <a href="http://en.wikipedia.org/wiki/Clausius-Clapeyron_relation" rel="nofollow">Clausius-Clapeyron equation</a> appe... | https://physics.stackexchange.com/questions/48302/calculating-the-fracdpdt-slope-using-clausis-clapeyron |
Question: <p>My Co-workers and I are trying to figure this out, but can't think of a logical answer. It's probably an easy one, but I'll ask anyway-
Ok, the heater is set at 73 degrees.
The a/c is set at 73 degrees.
Why does it feel warmer with the heat on if they're both 73 degrees?</p>
Answer: <p>1) Maybe it's you... | https://physics.stackexchange.com/questions/51739/heating-verses-air-conditioning |
Question: <blockquote>
<p>Health - Controversial New Idea: Nerves Transmit Sound, Not Electricity - By Robert Roy Britt, LiveScience Managing Editor
posted: 14 March, 2007 1:00 pm ET Rendering shows a biological membrane at its melting point. The green molecules are liquid, and the red are solid. Molecules of anest... | https://physics.stackexchange.com/questions/53447/the-physical-laws-of-thermodynamics-tell-us-that-electrical-impulses-must-produc |
Question: <p>I have a boiling pot of water that I am going to cook my Sponge Bob Noodles in. I am very hungry and want the noodles to cook faster, so I turn up the heat from medium to high.( Note, the water was already boiling at medium).What happens to the time it takes for my noodles to cook, and the temperature of... | https://physics.stackexchange.com/questions/54709/what-happens-to-the-time-it-takes-for-my-noodles-to-cook-and-the-temperature-of |
Question: <p>At what depth in the water atmospheric pressure is 100 times greater than on the ground?
This question comes from the fact that average pressure in Earth( 1000 mbar) is 100 times greater than in Mars( 7 mbar).</p>
Answer: <p>The atmospheric pressure at STP is 101325 N/m$^2$, so 100 times this is 1.01325 ... | https://physics.stackexchange.com/questions/53758/at-what-depth-in-the-water-atmospheric-pressure-is-100-times-greater-than-on-the |
Question: <p>Can I make a heat pump beat the Carnot efficiency? Why is the <a href="http://en.wikipedia.org/wiki/Carnot_cycle" rel="nofollow">Carnot process</a> the most efficient one?</p>
<p>If I have a heatpump that is sphere shaped, and cascaded in layers like a onion can I beat Carnot efficiency? Heat would be tra... | https://physics.stackexchange.com/questions/56576/most-efficient-type-of-heat-pump |
Question: <p>I once worked as a kitchen porter over a winter season.<br>
We had fun with thermal temperature guns (like <a href="http://www.amazon.co.uk/tag/infrared%20thermometer/products" rel="nofollow">these</a>) which I learned can be used for measuring the temperature of something a reasonable distance away (aside... | https://physics.stackexchange.com/questions/60115/how-does-a-thermal-temperature-gun-work |
Question: <p>I am designing a cooling system for my computer and had a few questions.</p>
<p>So I have a computer water cooling radiator and I want to cool it as much as I can.</p>
<p>My first two ideas were an old window A/C unit and blowing air over the cold radiator in there onto my radiator. Or put the whole radi... | https://physics.stackexchange.com/questions/60883/computer-cooling-with-dry-ice-ideas-and-question-thermodynamics |
Question: <p>Why do sublime solids sublimate in the first place? Is it that their melting point and their liquid's boiling point are the same so that they manage to magically skip the liquid phase? (if so, why does it have to be so?)And is the reverse possible?</p>
Answer: <p>$CO_2$ sublimates at atmospheric pressure,... | https://physics.stackexchange.com/questions/61801/phase-transition-by-sublimation |
Question: <p>I'm stuck on a problem that I found in a book (Modern Thermodynamic with Statistical Mechanics, Helrich S., problem 5.2).</p>
<p>The text of the problem is that:</p>
<blockquote>
<p>Consider a solid material for which:</p>
<p>$$
\frac{1}{\kappa_T} = \frac{\varepsilon}{2V_0}\left[\frac{2\Gamma c_v ... | https://physics.stackexchange.com/questions/62293/finding-equation-of-state-from-thermal-expansion-coefficient-and-isothermal-comp |
Question: <p>What is the work done by an ideal gas when final pressure and volume are both different from its initial pressure and volume or when both pressure and volume changes ?</p>
Answer: <p>The work done by the gas on the environment is $W = \int_{V_a}^{V_b} P(V)\text{d}V$, where $V_a$ and $V_b$ are the initial ... | https://physics.stackexchange.com/questions/62792/what-is-the-work-done-by-an-ideal-gas |
Question: <p>I was reading up on the Ideal Gas Equation in University Physics with Modern Physics by Young and Freeman when I chanced upon a seemingly illogical mathematical equation.</p>
<p>Can anyone rectify this error? Or is it misunderstanding on my part?</p>
<p>Here is the portion (Page 600, Chapter 18, Equation... | https://physics.stackexchange.com/questions/64026/error-in-sears-and-zemanskys-university-physics-with-modern-physics-13th-editi |
Question: <p>Goodday all, </p>
<p>I was recently reading up on a few projects that might be of interest to me when I found "CPU Bong water coolers", there isn't much online on them so I figure I would ask y'all.</p>
<p>If you do a quick google search you can see what this thing actually is. </p>
<p>They get a length... | https://physics.stackexchange.com/questions/64092/explain-to-me-how-this-water-cooler-works |
Question: <p>This is a two-part question...</p>
<p>Firstly, models of the specific heat capacity $C$ (i.e. Debye, Einstein) in relation to the temperature $T$ give $C$ as steadily increasing with $T$. I assume that the change in $C$ is due to the heat the system gains being stored in its degrees of freedom- so why doe... | https://physics.stackexchange.com/questions/6367/specific-heat-and-temperature |
Question: <p>Suppose you have two thermodynamical systems $X_1$ and $X_2$ (for example water and air) with different temperatures ($T_1 > T_2$). Now put them into thermal contact. Is there a formula which describes, how $T_1$ and $T_2$ changes with time?</p>
Answer: <p>In a simple heat conduction theory (no convection... | https://physics.stackexchange.com/questions/7764/time-dependence-of-temperature-equalization |
Question: <p>To maintain the surface tension which formed our original bubble (in order to keep the bubble from breaking), we may change the temperature/pressure of air on both sides of the bubble varyingly, with different rates.</p>
<p>Is such a configuration possible? Examples of any such system?</p>
Answer: <p>The... | https://physics.stackexchange.com/questions/7780/can-a-water-bubble-be-frozen-into-ice-bubble |
Question: <p>As compared to when the coffee is just hot from brewing. I suspect it has something to do with the way the microwaves are affecting the molecules of the coffee.</p>
Answer: | https://physics.stackexchange.com/questions/8542/why-is-it-when-you-microwave-cold-coffee-and-then-add-milk-it-creates-a-foam-hea |
Question: <p>I was doing some reading on wikipedia and found it interesting that one page says the Grand Canonical Ensemble does not allow for exchange of particles, however another page says it does. So I went on google books and tried to look for a more trust worthy source, again the same happens one source says it a... | https://physics.stackexchange.com/questions/8714/does-the-grand-canonical-ensemble-allow-for-exchange-of-particles-or-not |
Question: <p>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 for a constant volume, isothermal process where the pressure is increased by adding moles of a gas?</p>
Ans... | https://physics.stackexchange.com/questions/9189/work-for-constant-volume-compression-by-adding-moles-of-gas |
Question: <p>My question is mainly an engineering question. Assume I have a turbine in which I adiabatically expand compressed air. The air cools down and does work to its surroundings, which is captured by the blades of the turbine and then is transformed into rotational energy/electricity. </p>
<p>When instead I let... | https://physics.stackexchange.com/questions/9494/free-adiabatic-expansion |
Question: <p>If a fan that is using 50 watts is moving 1 m³/min of air. Lets say the walls are the same temperature as the air so there’s no heat dissipation there. How do I know if the fan is putting in more energy in to the room than its dissipating?</p>
<p>If the walls are 10 deg cooler than the air will this be su... | https://physics.stackexchange.com/questions/11428/a-fan-in-a-hot-room-at-what-point-does-it-put-in-more-energy-that-it-dissipates |
Question: <p>In the Wikipedia article on <a href="http://en.wikipedia.org/wiki/Maxwell%E2%80%93Boltzmann_statistics" rel="noreferrer">Maxwell–Boltzmann statistics</a>, there is a point in the derivation that stumps me. When I get to where</p>
<p>$\displaystyle W=N!\prod\frac{g^{N_i}}{N_i!}$</p>
<p>is quoted as a cou... | https://physics.stackexchange.com/questions/15129/trying-to-understand-a-step-in-deriving-maxwell-boltzman-statistics |
Question: <p>In more detail:
If i have two soda cans, both are cooled to exactly 4 degrees celsius,
And i put one in a 25 degrees room, and the other next to an AC vent set to 16 degrees.
After three minutes, which one should be colder than the other and why?</p>
<p>Edit: To clarify - if I have a cold soda can, should... | https://physics.stackexchange.com/questions/16076/is-the-cooling-rate-of-a-very-cold-object-sitting-next-to-an-ac-higher-or-low |
Question: <p>There is a closed system that is just a windmill attached to a rotating shaft that can mechanically power something. I know the system produces work on the surroundings from the rotating shaft and this is positive work, but is there also a negative work input from the wind pushing the blades of the windmil... | https://physics.stackexchange.com/questions/16976/thermodynamic-system-windmill |
Question: <p>My native language is not English and I am having hard time understanding the meaning of the following statements which are to explain the laws of thermodynamics. </p>
<ol>
<li><p>The 1st law: you cannot win (meaning that I cannot make a profit?)</p></li>
<li><p>The 2nd law: you cannot break even (I looke... | https://physics.stackexchange.com/questions/17383/meaning-of-what-c-p-snow-said-about-the-laws-of-thermodynamics |
Question: <p>Is there an equation I can use to calculate the heat required (as a function of time) to sustain water at some specif temperature?</p>
<p>I already know how much heat I need to reach the desired temparature using the formula Q=m*cp *(T2-T1). My question is how much heat do I need to keep 30,000lts of wate... | https://physics.stackexchange.com/questions/17686/how-much-heat-i-need-to-reach-constant-temperature |
Question: <p>I need some ideas on a problem. </p>
<p>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. ($\Delta T = \frac{g*h}{c_{H_2 O}}$)</p>
<p>The second part asks what factors tend to prevent that rise in ... | https://physics.stackexchange.com/questions/21395/in-the-niagara-falls-which-factors-prevent-rise-of-t-h2o-falling-a-certain-heig |
Question: <p>This is a somewhat philosophical question. Given that even after person A's death, there's a non-zero chance that a brain fluctuates into existence with exactly the same structure and memories as A's brain, does that imply that A is immortal as given enough time, even if for each fluctuation, it survives f... | https://physics.stackexchange.com/questions/23013/boltzmann-brain-immortality |
Question: <p>Suppose I have a ceiling and its dimension are given in $Z \times C \times Y$, and a it's got a thermal conductivity $k$. Now, I want to know H, or the heat rate. It's given by $ H =\frac{kA(T_h -T_c)}{L}$. Where $T_h \ and \ T_c$ are the hot and cold temperature difference. How do I use the given dimensi... | https://physics.stackexchange.com/questions/28074/about-heat-rate-and-dimensions-convention |
Question: <p>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.</p>
<p>How does this affect the entropy of the system? How can I calculate the change in entropy?</p>
Answer: <p>Entropy is an <a href="htt... | https://physics.stackexchange.com/questions/30039/how-does-the-entropy-of-a-system-change-when-the-amount-of-substance-changes |
Question: <p>Assume you have a reasonably well thermally insulated box of air which you want to keep warm. It has at least one heat source, and it has at least one heat sink. One of the options available to you is to attach a second volume to the first, on the bottom of it, hoping to rely on the idea that the coldest a... | https://physics.stackexchange.com/questions/413865/how-does-a-lower-elevation-volume-affect-the-temperature-of-the-volume-above-it |
Question: <p>Why must the material of heating element of an electric heater habe high resistivity ? I mean, more resistivity, more resistance and hence less current and current is directly proportional to heating effect. And ive read that it is because if current is increased then resistance will decrease but heating e... | https://physics.stackexchange.com/questions/414968/heating-effect-of-current |
Question: <p>Consider a system having spherical symmetry filled with gas. If it expands or compress, there is some work done by system or surroundings, respectively, according to the equation $W=nRT\log(v_2/v_1)$. But the coordinates of centre of mass of system is same at the centre of sphere, so according to original ... | https://physics.stackexchange.com/questions/419911/understanding-the-meaning-of-thermodynamic-work-more-clearly |
Question: <p>When co2 is released from the cartridges. Is the gas get cold too or just the cartridge itself only ? And will be releasing it slowly will effect the temper drop ? Thanks you</p>
Answer: <p>It is an imprecise question. But then, once we know exactly what question to ask, we almost always have the answer ... | https://physics.stackexchange.com/questions/420278/co2-cartridge-questions |
Question: <p>In my book,it is given that hot bar placed under a running tap loses heat by conduction. My question is that why it can't be convection as the movement of water molecules is involved.</p>
Answer: <p>The cooling here obviously involves the movement of material, so, by definition, it is a form of convection... | https://physics.stackexchange.com/questions/424157/a-hot-bar-under-tap-water-loses-its-heat-by |
Question: <p>I should determine the spontaneous magnetization of an ferromagnet below its critical temperature <span class="math-container">$T_{c}$</span> by only knowing the derivatives:</p>
<p><span class="math-container">$$
\left ( \frac{\partial M}{\partial H } \right )_{T}=\frac{a}{1-T/T_c}+3bH^{2}
$$</span>
wher... | https://physics.stackexchange.com/questions/432120/obtain-magnetization-from-derivatives |
Question: <p>In the first law of thermodynamics, We write the change in internal energy in terms of heat exchanged and work done. The answer to the above question doesn't matter if our final aim is to find the change in internal energy. However, When calculating the efficiency of an irreversible cycle, We always write ... | https://physics.stackexchange.com/questions/434405/is-the-work-done-by-friction-considered-as-heat |
Question: <p>Isn't thermal expansion and laws of thermodynamics contradictory?
Gas expands when heated, but after expansion it cools down.</p>
Answer: <p>One of the first things to learn in thermodynamics is the importance of explicitly stating the conditions of a transformation. Speaking of thermal expansion and coo... | https://physics.stackexchange.com/questions/441481/thermal-expansion-and-thermodynamics |
Question: <p>So my book claims that under constant-pressure conditions, the change in enthalpy is given by <span class="math-container">$dH=Q$</span>. However, if we look at the thermodynamic identity and first law of thermodynamics, we see that
<span class="math-container">$$
dU=TdS-PdV+\sum_i\mu_idN_i=Q+W.
$$</span>
... | https://physics.stackexchange.com/questions/446187/why-isnt-dh-q-sum-i-mu-idn-i-constant-pressure |
Question: <p>I'm currently trying to reproduce a specific derivation of the caloric equation of state for the Van der Waals gas, which I saw a couple of months ago in a Thermodynamics lecture. I'm well aware of the fact that there are already multiple derivations on this site and online (see <a href="https://physics.st... | https://physics.stackexchange.com/questions/453594/caloric-equation-of-state-for-the-van-der-waals-gas |
Question: <p>Suppose that we have 2 objects and both of them reached thermal equilibrium. Do the particles of the two objects still collide with each other? If so, do any of the collisions result in the transfer of energy between the two objects? Explain.</p>
Answer: <p>Microscopically the particles of the two bodies ... | https://physics.stackexchange.com/questions/453691/will-the-particles-from-2-objects-in-thermal-equilibirum-still-collide |
Question: <p>We are told by our chemistry teacher that all chemical reactions take place as reactants (that have bigger potential) change into products (that have smaller potential) hence unstable substances change into more stable ones. But doesn't this mean "all reactions are exothermic"? I am in need of a clarificat... | https://physics.stackexchange.com/questions/455551/how-do-all-chemical-reactions-result-in-a-product-whose-potential-is-less-than-t |
Question: <p>Taking an adiabatic process as example , from the first law of thermodynamics <span class="math-container">$$\Delta U=-W... (1)$$</span> .Now if I pull up the piston applying force from my side , the work is done by me on the system so the sign is negative, so from (1) , <span class="math-container">$\Delt... | https://physics.stackexchange.com/questions/459600/why-would-the-gas-do-work-when-the-piston-is-pulled-by-external-force |
Question: <p>In the proof of :</p>
<p><span class="math-container">$$dU=C_v dT - \left[T \left( \frac{\partial P}{\partial T} \right)_V - P\right] dV$$</span></p>
<p>on wikipedia <a href="https://en.wikipedia.org/wiki/Internal_energy" rel="nofollow noreferrer">https://en.wikipedia.org/wiki/Internal_energy</a>, they u... | https://physics.stackexchange.com/questions/463100/how-to-know-the-dependances-of-thermodynamic-variables |
Question: <p>Consider a metal rod between two bodies of different temperature.How do you explain the occurrence of steady-state when heat Is transferring by conduction through the rod. I mean why should there exist a point called steady-state in the first place, meaning why the temperature of the rod at a point become ... | https://physics.stackexchange.com/questions/477612/heat-transfer-and-steady-state |
Question: <p>The Joule-Thomson coefficient is given by
<span class="math-container">$$\mu_{JT} = \left(\frac{\partial T}{\partial P}\right)_{H} = \frac{V}{C_{P}}(\beta T - 1),$$</span>
where <span class="math-container">$\beta$</span> is the coefficient of thermal expansion. If the inversion temperature is defined by ... | https://physics.stackexchange.com/questions/483132/joule-thomson-effect-why-does-a-gas-cool-if-its-below-the-inversion-temperatur |
Question: <p>In isothermal process if the internal energy is not increasing then how does the pressure change?</p>
<p>I come to the question because in isobaric process the pressure remains unchanged because the change of volume and temperature . But in isothermal process the the temperature is not changed but pressur... | https://physics.stackexchange.com/questions/484915/change-of-pressure-in-isothermal-process |
Question: <p>Recently I saw a question where there was a specific p-v relation for a process, but it was stated that it's not a quasi-static process. Hence, we can not calculate the work done by integration of pdv work. </p>
Answer: <p>You can can calculate the work done by integrating <span class="math-container">$pd... | https://physics.stackexchange.com/questions/485814/can-a-non-quasi-static-process-have-an-equation-of-the-path-which-it-has-followe |
Question: <p>I came across this definition of the first law of thermodynamics in <a href="https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Thermodynamics/Energies_and_Potentials/Differential_Forms_of_Fundamental_Equations"... | https://physics.stackexchange.com/questions/489305/how-can-heat-be-a-inexact-differntial-in-thermodynamics |
Question: <p>A thermodynamic question: is electromagnetic radiation released because of a difference in temperature or because instability of electrons inside matter (atoms and molecules)?</p>
<p>The thermodynamic law states that energy goes from higher temperature to lower temperature in my study book, but I think th... | https://physics.stackexchange.com/questions/489330/is-electromagnetic-radiation-released-because-of-a-difference-in-temperature-or |
Question: <p>I was wondering what is the ideal number of glass layers in a windows assuming outside T2 is greater than inside T1 and we want T1 to remain as low as possible (ie. keep the room cool). Now heat capacity (C) and thermal conductivity (λ) of air between glass layers is lower than that of glass but having no ... | https://physics.stackexchange.com/questions/493287/heat-transfer-through-window |
Question: <p>There is a limit of temperature that is about <span class="math-container">$0$</span> K = <span class="math-container">$-273.15$</span> <span class="math-container">$^\circ$</span>C. Is there any maximum limit?</p>
Answer: <p>Nope. Not really. (I need 30 characters) </p>
| https://physics.stackexchange.com/questions/501196/thermodynamic-planks-temperature |
Question: <p>So I was studying the carnot cycle and was taught it as the following sequence.</p>
<p>Imagine a cylinder filled with some ideal gas at <span class="math-container">$T_1$</span>. It has some rocks on top of it and the system is in equilibrium.
If you place it in a reservoir at temperature <span class="ma... | https://physics.stackexchange.com/questions/507397/queries-about-the-carnot-cycle |
Question: <p>When introduced to the gibbs free energy, it was derived as follows:</p>
<p>First law: <span class="math-container">$dU=dq+dw$</span></p>
<p>Second law: <span class="math-container">$dS>dq/T$</span> for a spontaneous change.
Note <span class="math-container">$dq$</span> and <span class="math-container... | https://physics.stackexchange.com/questions/511775/question-about-description-of-gibbs-free-energy |
Question: <p>While I was imagining about carnot engine I got this question whether we can achieve a 100% efficient engine in other dimensions?</p>
Answer: <p>The efficiency of the most efficient engine or Carnot engine is given by <span class="math-container">$n=1-{Q_2\over Q_1}$</span></p>
<p>For <span class="math-c... | https://physics.stackexchange.com/questions/513479/can-efficiency-of-a-normal-engine-in-other-dimensions-be-100 |
Question: <p>Suppose we have a heat insulated and rigid container with a frictionless piston dividing the container into two parts, the left part being filled with some ideal gas(say mono-atomic), and the right one is vacuum with a spring connected between the right wall and the piston. How do we decide what process th... | https://physics.stackexchange.com/questions/523749/how-to-decide-whether-the-process-is-polytropic-quasistatic-both-or-neither |
Question: <p>One question that was posed to me was this: if two otherwise identical blocks are at <span class="math-container">$100$</span> and <span class="math-container">$0$</span> degrees Celsius, and for clarity the hot block is red and the cold block is blue, what is the maximum difference in temperature between ... | https://physics.stackexchange.com/questions/530814/heat-exchange-between-two-blocks |
Question: <p>While cooking, I have noticed that a ball of boiled spinach retains its heat for a long time. I understand that spinach is 91% water. It is my hunch that the same volume of water would cool much faster. If 9% of spinach is attributable to other compounds, my first guess might be that water would cool only ... | https://physics.stackexchange.com/questions/533336/shape-complexity-of-a-substance-and-its-effect-on-heat-retention |
Question: <p>My question differs from these questions:</p>
<ol>
<li><a href="https://physics.stackexchange.com/questions/336945/when-is-delta-u-nc-v-delta-t-true">When is $\Delta U=nC_V \Delta T$ true?</a></li>
</ol>
<p>Because here he asks to distinguish between <span class="math-container">$C_P$</span> and <span cl... | https://physics.stackexchange.com/questions/550621/why-is-delta-u-nc-v-delta-t-true-intuitively-regardless-of-the-path |
Question: <p>Every evening I am preparing hot water for my two year old son wakes up in the night to get his milk. We use a rather bad isolation can for this. It is a typical metal cylinder shaped can holding half a liter. If I put cooking hot water into it, I know that about 5 hours later it will have room temperature... | https://physics.stackexchange.com/questions/551001/should-the-thermos-flask-better-be-half-full-or-half-empty |
Question: <p>I am reading heat and thermodynamics by Zemansky and while defining heat capacities at constant pressure and volume, it is said that heat capacity at constant pressure is a function of <span class="math-container">$P$</span> and <span class="math-container">$T$</span>. Why not V? and likewise for heat capa... | https://physics.stackexchange.com/questions/557382/why-is-heat-capacity-at-const-pressure-c-p-not-a-function-of-volume |
Question: <p>Is it possible to practically build a perfectly insulating container? If not, what's the best way to build one? By perfectly I mean no heat is trasferred over an infinite amount of time.</p>
Answer: <p>As Harish Chandra Rajpoot removed his answer instead of rectifying to:</p>
<p>"No, it is not possib... | https://physics.stackexchange.com/questions/559108/insulating-container-in-real-life |
Question: <p>I'm trying to figure out what temperature actually is, and there seem to be a lot of answers floating around:</p>
<ul>
<li><a href="https://web.stanford.edu/%7Epeastman/statmech/thermodynamics.html" rel="noreferrer">average kinetic energy per degree of freedom</a></li>
<li><a href="https://physics.stackexc... | https://physics.stackexchange.com/questions/570445/how-do-thermometers-actually-function |
Question: <blockquote>
<p>It is found that all known
gases cool slightly on undergoing a free expansion. This is consistent with the
kinetic theory idea that temperature is associated with the kinetic energy of
the molecules.
<em>If the gas expands</em>, <strong>then the intermolecular attraction potential
energy goes ... | https://physics.stackexchange.com/questions/593663/gas-free-expansion |
Question: <p>I've seen some interesting analogies explaining why exactly Work and Heat are path function. One where the floors of a building describe the gravitational potential energy, while stairs and elevator are the two paths one can take to reach between the two states of energy.</p>
<p>But my question is how woul... | https://physics.stackexchange.com/questions/595213/why-is-work-and-heat-path-function-what-different-paths-can-they-take |
Question: <p>I am reading the book "Thermodynamics" by Enrico Fermi. There is a passage that goes like this:</p>
<blockquote>
<p>It is evident from what we have said that the knowledge of the
thermodynamical state alone is by no means sufficient for the
determination of the dynamical state. Studying the therm... | https://physics.stackexchange.com/questions/608496/why-is-the-knowledge-of-the-thermodynamical-state-alone-is-by-no-means-sufficien |
Question: <p>I was studying the stability of thermodynamic potentials. It is obvious that internal energy is a convex function of <span class="math-container">$(S,V) $</span>, and in case of instable circumenstances, the system adjust in such a way that the global and local convexity law, is well respected. However, It... | https://physics.stackexchange.com/questions/629169/phase-transition-stability-of-thermodynamic-potentials |
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