Temperature Definition and 1000 Threads

Temperature is a physical quantity that expresses hot and cold. It is the manifestation of thermal energy, present in all matter, which is the source of the occurrence of heat, a flow of energy, when a body is in contact with another that is colder or hotter.
Temperature is measured with a thermometer. Thermometers are calibrated in various temperature scales that historically have used various reference points and thermometric substances for definition. The most common scales are the Celsius scale (formerly called centigrade, denoted as °C), the Fahrenheit scale (denoted as °F), and the Kelvin scale (denoted as K), the last of which is predominantly used for scientific purposes by conventions of the International System of Units (SI).
The lowest theoretical temperature is absolute zero, at which no more thermal energy can be extracted from a body. Experimentally, it can only be approached very closely (100 pK), but not reached, which is recognized in the third law of thermodynamics.
Temperature is important in all fields of natural science, including physics, chemistry, Earth science, astronomy, medicine, biology, ecology, material science, metallurgy, mechanical engineering and geography as well as most aspects of daily life.

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  1. Omaha

    Looking for ideas for a propane burner design

    I make custom cast bronze decorative motorcycle parts using lost wax investment casting. I'm looking to improve the precision and reliability of my casting process (currently getting maybe 25% duds over time). My current initiative is to improve my temperature control on the shells prior to...
  2. joejoe121

    A 50 cubic foot tank contains saturated 134a at 100F and a quality of 50%

    I've attached all my work and data table I used to answer the questions but there isn't an answer key so I would like a second opinion. a) The initial specific internal energy is.......Btu/lbm b) The initial mass is....lbm c)The average enthalpy of the withdrawn vapor is.....Btu/lbm d)The final...
  3. J

    Doubt about old electrolytic capacitors

    I have stored here electronic devices with aluminum electrolytic capacitors used and manufactured in the early 90s. Here the temperature varies between 33-35C. These electronic devices need to be energized what time and frequency to prevent failures in these aluminum electrolytic capacitors...
  4. L

    Thermodynamics of a Heat Engine - (First/Second Law)

    and the solutions: I am not sure why two of the bodies are at the same temperature to end with. I am pretty certain that they don't have to be - but the author of the problem set it this way for some reason I'm missing (my guess). My reasoning: Put 100 K and 300 K together for a short time...
  5. J

    Thermal exchange between warm object and ideal gas

    The total variation of internal energy states ##\Delta U_{tot} = 0## ##\Delta U_{tot} = \Delta U_{ext} + \Delta U_{gas} + \Delta U_{obj}## with: ##\Delta U_{ext} = Q_{ext} - W_{ext} = -W_{ext}## ##\Delta U_{gas} = Q_{gas} - W_{gas} = Q_{gas} - ( - W_{ext} ) = Q_{gas} + W_{ext}## ##\Delta U_{obj}...
  6. P

    A Temperature calculation for combustion chamber

    Hi! I was wondering if it is possible to calculate the temperature near the roof of combustion chamber based on thermocouple reading which is located at nine o'clock position. Tip of measuring device is located 49 mm from the surface of hot face material. Please find the picture attached...
  7. tellmesomething

    Temperature dependence of resistance

    I wanted to find the differential form of the above equation and i get $$\frac{dR(t)}{dt}=R_{0}\alpha$$ (##t_{0}##=0 degree celsius) So $$\alpha=\frac{dR(t)}{dt} \frac{1}{R_{0}}$$ (##\alpha##= temperature coefficient of resistance ##R_{0}##=Resistance at temperature 0 degree celsius) This idea...
  8. Alan Todd

    B Adiabatic processes and temperatures

    Do adiabatic processes maintain temperatures? That is, can temperatures remain constant during adiabatic processes?
  9. F

    Temperature of two subsystems at equilibrium

    I was going through the textbook Thermodynamics and an Introduction to Thermostatistics by Herbert B. Callen, and in Chapter 2.4 of the book, the author proves that given two subsystems separated by an impermeable and immovable wall which only allows for the transfer of heat, the temperature of...
  10. hraghav

    Find the final temperature of the combined honorite and odium?

    Qmelt, honorite = (m honorite)⋅(Lfusion, honorite) Qmelt, honorite = 4.51kg⋅15500J/kg = 69905J Qcool, odium = (m odium)⋅(Cliquid, odium)⋅(391.14K−331.44K) Qcool, odium = 14.69kg⋅431.1J/kgK⋅(391.14K−331.44K) Qcool, odium = 378071.6823 Qfreeze, odium = (m odium)⋅(L fusion, odium) Qfreeze, odium...
  11. hraghav

    Find final temp of 2 substances once they have reached equilibrium

    Cooling Lerasium to its melting point: Q1 =m L⋅c L,liquid ⋅(T L,i −T L,melt) Q1 = 1.49kg⋅221.6J/kgK⋅(1108.1−56.4)K Q1 = 330.184 ⋅(1051.7) = 347254.512 J Heating Atium to its melting point: Q2 =mA⋅cA,solid ⋅(TA,melt −TA,i) Q2 = 2.44kg⋅524.8J/kgK⋅(308−33.6)K Q2 = 1280.512⋅(274.4) = 351372.493 J...
  12. S

    Looking for a chemical with a boiling point between 10C and 50C

    i am looking for a chemical compound that has a boiling or condensation temperature between 10C and 50C at standard pressure and is not one prohibited for discussion in the Physics Forum or any online chemical forums. something that is organic and not very toxic is preferred. it should be...
  13. M

    How to predict the exit temperature of an air compressor?

    It’s been said that an air compressor could be “idealized” as a reversible adiabatic process in which case calculating the properties of the gas at the exit would be simple. The problem is, it rarely seems to be the case, in practice, that the process is reversible so how useful is this...
  14. hraghav

    Find temperature of a U-shaped Tube

    So first I used the ideal gas law formula PV = nRT to find n using P = 101000Pa, V = 1.81m^3, R = 8.314 J/mol*K^-1, T = 24.3+273.15 = 297.45K. I got n = 73.922 mol. Then I used P = density*g*h and found P = 2132.48 where density = 2560kg/m^3, g = 9.8 and h = 0.085m. Then I found total pressure...
  15. E

    Appliances Is Your GE Fridge Cooling Unevenly?

    I have a GE refrigerator( side by side ) about 11 years old now. I noticed warm milk yesterday. The set points for the freezer/fridge are 0 F and 37F respectively, and the actual temps are -7F and 55F. It seems like the freezer is running constantly, and the fridge side can get a word in...
  16. S

    B Why did making the recovery tank cold expedite recovery of refrigerant?

    Many years ago, I was a student in a HVAC program at a technical college. Sometimes when I and the other students were recovering refrigerant out of an air conditioner into a recovery tank, we would get ice from the ice machines and fill up a tub with ice, and then we would put the recovery tank...
  17. ergospherical

    I What temperature would 1 keV neutrinos have today?

    Suppose there was a 4th generation of neutrino (X, say) with mass m ~ 1 keV. The other three neutrino generations decouple at T ~ 1 MeV and are not heated during ##e^{\pm}## annihilation (whereas the plasma is heated, leading to a bookwork ##T_{\nu}/T_{\gamma}## factor due to conservation of...
  18. AmanWithoutAscarf

    Effect of temperature on surface tension

    The translated version is: 1. 2. I did research on the topic and the Eötvös rule, but most of the results are just qualitative explanations or experiment-based proofs of the temperature-dependent function of surface tension. Can anyone give me some hints on how to prove that linear...
  19. N

    I Viewing 1k x 1k slab of desert sand during extreme cold/hot temps?

    So, non-quartz sand has 1/2 mm kernels, they can be seen as individual objects from about 60cm distance. Standing in front of it, about a half of the individual sand kernels beam each separately into your pupil, so 500,000 discrete beams, each covers almost the entire pupil. Yet, you see a...
  20. D

    Mathematica Black Hole shadow temperature profile

    I am not sure if it is right to ask this question or not. Kindly let me know if it isn't. Actually I was going through the article Shadow Thermodynamics. I was trying to recreate the image fig 5 and 6 in mathematica. The idea is that we have to draw circles of radius ##r_s## given by equations...
  21. srfriggen

    I Antipodal points and temperature and other angles

    Hello, I am a high school math teacher and recently presented my students with an intriguing problem: "At any given moment, there are two antipodal points on Earth (180 degrees apart) that have the same temperature." This can be demonstrated using one great circle with two opposite points. If...
  22. N

    I Permittivity (epsilon) change via temperature + optics effect?

    I got this from chatgpt: It says "not simple and straightforward", but can we assume proportional ? So is there a visible alteration in Snell angle ? Also, for applied physics databases, what would be a pubmed equivalent, hosting all titles and synopses ? In physics the articles seem to be...
  23. J

    Max inversion temperature for a gas (Dieterici’s equation of state)

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  24. A

    Temp change of copper wire w.r.t. time for a constant applied voltage

    Q=m.c.DeltaT, is one approach which could possibly give the relation between Power vs Time. Is it correct ?
  25. yecko

    Superheater - pressure and temperature distribution

    Quoted from the O&M manual of an electrical steam superheater: "The Steam Superheater has eight thermocouples of the NiCr-Ni type, known as "K," attached to the heating element sheath. Four of these thermocouples are positioned near the steam outlet nozzle, where the highest temperature is...
  26. A

    Equation of resistance from given graph

    From the graph: $$lnR(T)=\frac{-lnR(0)T^2_○}{T^2}+lnR(0)$$ I have assumed ##R(0)## to be the value of ##R## at ##1/T^2=0## and ##T_○## to be the value of ##T## at ##lnR(T)=0## From this I get, $$R(T)=e^{lnR(0)×\left(1-\frac{T_○^2}{T^2}\right)}$$ $$R(T)=R(0)^{\left(1-\frac{T_○^2}{T^2}\right)}$$...
  27. M

    I Experiment on the variation of weight with temperature

    Hello ! According to what I have read on the internet, the weight of a body varies with temperature, its mass remaining unchanged according to the theory of relativity. My question is what experiment is done to corroborate that the weight of a body increases with the increase in its...
  28. J

    B How Is Solar Wind Temperature Measured?

    I read that the solar wind is a stream of particles, primarily electrons and protons, flowing out from the sun at speeds as high as 900 km/s, and at a temperature of 1 million degrees. Using the equipartition theorem, I calculate that a proton moving at 900,000 meters per second exhibits a...
  29. Dante Meira

    B Speed of sound in steel at different temperatures?

    Is there a formula to calculate the speed of propagation of sound waves through steel (a steel bar, for example) according to the temperature of steel?
  30. S

    I Calculation of temperature changes (heating a cube in a microwave oven)

    Hello guys, I am currently running an experiment in my hobby room: I want to heat a cube in a microwave and then measure the surface temperature. Unfortunately, it takes about 20 seconds, so the cube cools down during this time which means I don't measure the actual temperature after heating...
  31. J

    What happens to the IR radiation that the Greenhouse gases don't absorb?

    I have been searching for the answer yet – as I'm here – didn't find it. The current model of climate warming says the lower parts of Earth's atmosphere don't allow the IR radiation to escape freely to the outer space because the GH gas molecules keep absorbing it virtually as soon as it's been...
  32. L

    B What would happen to perception if temperatures almost reached absolute zero?

    Say there was something that made the temperature of the universe almost absolute zero, but around you was a mini bubble where the temperature was normal, and therefore molecules could move normally around you for a small area. How would you perceive the world around you outside of the little...
  33. K

    What Set Temperature Achieves 900C Without Controller Offset?

    How to incorporate deviation -9.2C in furnace, while its measured temperature is 909.2C and Display temperature is 900. if there is no option of offset in controller. What will be the set temperature to achieve 900C.
  34. C

    I Thermodynamic temperature scale and Carnot cycle

    Hi all, recently I started following the MIT course "Statistical Mechanics I: Statistical Mechanics Of Particles" by MIT (here). In the second lesson Prof. Kardar introduces the concept of thermodynamic temperature analyzing the behavior of two Carnot engines that share a thermal reservour at...
  35. Z

    Log-log graph of resistance against temperature for a carbon resistor

    (a) (b) Here is a plot of this function T of R It seems that as the resistance goes up the temperature goes down. Not sure what to make of this physically speaking. My question is about the requested log-log graph. Above we have a function T of R, but we want a function ##\log{T}## of...
  36. Sasho Andonov

    B What is the Volume of the Plasma Inside the LHC During Particle Collisions?

    Could someone provide an ainformation what is the temperature inside the Large Hadron Collider (or similar systems) where the colision of particles happens? THANK YOU!!!!
  37. Z

    Calculate ideal-gas temperature of a material

    Here is the table As far as I can tell what we have here are four constant-volume thermometers (each column represents a thermometer). These thermometers work by having a certain constant volume of some specific gas in a bulb. We immerse the bulb in whatever temperature we would like to measure...
  38. eneacasucci

    I Variation of air temperature with altitude

    Considering the approximation of perfect gas, I don't understand why at higher altitude the temperature is lower. Intuitively it is clear to me, but I do not understand the kind of transformation that takes place; the gas is free to expand and the pressure too is not constant, since it decreases...
  39. Z

    I Constant length metallic wire as a thermometer, using tension?

    I posted another question about a thermodynamic system with three coordinates, namely, that of a metallic wire. We can describe that system with temperature, wire tension, and wire length. The result derived in that question was that the partial derivative of wire tension relative to absolute...
  40. Z

    I Empirical temperature scales using different thermometers

    It took me a while to understand (I think) the concepts below. I have two questions. 1) What does "absolute" mean in the term "absolute temperature scale"? 2) What is the difference between the two constant-volume hydrogen gas thermometers (one at high pressure the other at low pressure)...
  41. S

    Relationship between pressure and temperature for liquids

    ^^
  42. T

    I Relation between change of pressure and temperature in adiabatic process

    In case of adiabatic process, we all know that the relation between temperature and pressure and that's given below: P. T(γ/(1-γ)) = Const. therefore, P = Const. T(γ/(γ - 1)) or, ΔP = Const. (γ/(γ - 1)).ΔT(1/(γ - 1)) It's just an attempt to find out the relation. Don't know how much correct I...
  43. B

    How do we derive the Earth's yearly mean temperature?

    I'm new to this. I would like to know how we derive the earth's yearly mean temp. I assume there are thermometers all over...
  44. H

    The effects of absolute zero temperature

    I can visualize gas molecules, contained in a vessel, randomly bouncing into each other. As temperature increases, the collisions occur more rapidly. I suppose this also applies to liquids. I'll guess that a liquid's boiling point is where the molecular collisions become so violent that...
  45. Edy56

    Engineering Calculate voltage and temperature for this temperature-dependent resistor

    Is my work correct?
  46. xpell

    B At what distance would a Venus-like planet have a HZ temperature?

    Well... that: Please, could you please assist me in obtaining a rough estimate of the distance from the Sun at which a planet resembling Venus or a hypothetical Venus-like planet (for the sake of simplicity) would have a habitable-zone surface temperature? A "back-of-the-envelope" educated...
  47. E

    Details regarding the high temperature limit of the partition function

    My main question here is about how we actually justify, hopefully fairly rigorously, the steps leading towards converting the sum to an integral. My work is below: If we consider the canonical ensemble then, after tracing over the corresponding exponential we get: $$Z = \sum_{n=0}^\infty...
  48. M

    Why must we use absolute temperature for the Ideal Gas Law?

    For this problem, The solution is, However, why must we use absolute temperature for the ideal gas law (i.e why can we not use Celsius for T) Many thanks!
  49. Roger Dalton

    Dependence of Hall coefficient on temperature in semiconductors

    My first assumption is that the temperature dependence on the mobilities can be neglected, and so we would have: $$R_H(T)= \frac{1}{e} \frac{p_v(T)\mu_h^2-n_c(T)\mu_e^2}{(p_v(T)\mu_h+n_c(T)\mu_e)^2}$$ The expression for the electron and hole densities could be derived from...
  50. E

    Photoluminescence at lower temperature of carbazole

    Hello everyone, I deposit a thin film of HTM based carbazole and I measure the PL at lower tempertaure . by fiiting the experimental results with 5 peaks . I notice the dissapering of peak 1 at 300K and peak 3 at 200K. What is the nature of the interaction that can occur at lower temperature of...
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