What is Temperature: Definition and 999 Discussions

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. S

    Relationship between pressure and temperature for liquids

  2. 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...
  3. 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...
  4. 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...
  5. Edy56

    Engineering Calculate voltage and temperature for this temperature-dependent resistor

    Is my work correct?
  6. 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...
  7. 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...
  8. C

    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!
  9. 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...
  10. 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...
  11. A

    Oven controller block diagram, transfer function and temperature calcs

    FIGURE 5 shows an electrically heated oven and its associated control circuitry. The current, I, to the oven's heating element is fed from a voltage-controlled power amplifier such that I = EK1. A voltage, VD, derived from a potentiometer, sets the desired oven temperature, TD. The oven...
  12. S

    Experiment about diode related to temperature and potential difference

    (a) I know some of the apparatus needed for the experiment, such as DC power supply, ammeter, voltmeter, maybe rheostat. But I don't know how to change the temperature of diode. What is the correct and safe way to change the temperature of diode? Thanks
  13. H

    A Determination of electron temperature in an ion source

    How to correctly determine the temperature of electrons in an ion source based on ECR? Is it possible to use the Saha equation? ##\frac{n_en_i}{n_a}=\frac{g_eg_i}{g_a}*3*10^{21} T^{3/2} e^{-J/T}## Using the search, I found the McWhirter criterion for the applicability of the formula above: ##n_e...
  14. Wrichik Basu

    Any advice to make this Op-Amp temperature controller circuit work?

    As part of our UG curricula in Physics major, we have a practical in which we have to draw the calibration curve of an NTC ##10~\mathrm{\Omega}## thermistor, and then construct a circuit to maintain the temperature of a water bath. The calibration curve of our thermistor. The Prof. said that...
  15. dextercioby

    I Interpretation of temperature in liquids/solids

    Usually, the mental image of temperature is: an internal property of a bulk of matter, which typically describes the average kinetic plus rotation/vibration energy of molecules, so we imagine a gas in which temperature is a measure of how quick molecules are, and how frequently they collide one...
  16. Thomas_Kellner

    Change in temperature of air in a closed system

    Looking at the given values, I thought the specific heat formula could be used to calculate the final temperature of the air: c = Q/mΔT. Since the final temperature is the sum of the initial temperature and the change in temperature, the formula can be rearranged to ΔT = Q/m*c. Q = 30 W * 10 s...
  17. Ebi Rogha

    Gas temperature in a constant volume

    An insulated container (constant volume, adiabatic) contains an Ideal gas with pressure P1 and temperature T1. We open the container's hatch for a few seconds and let some particles escape from the container, then we close the hatch again. We know container's pressure has reduced by exiting...
  18. C

    Thermal expansion of square from temperature increase of 50K

    For this problem, The solution is, I understand their logic for their equation, but when I was trying to solve this problem, I came up with a different expression: ##\Delta A = \Delta L_x\Delta L_y## ##\Delta L_x =\Delta L_y = \Delta L## since this is a square. ##\Delta A = \Delta L^2##...
  19. H

    Temperature after closing the valve

    I have the following task and I am not getting anywhere: A steel tank with 15 m³ volume, well insulated from the outside, contains air at a temperature of 288 K and a pressure of 1 bar. It is connected to a compressed air line via a valve that is initially blocked. which constantly supplies...
  20. F

    A Average temperature in a greenhouse

    Hello everyone, since several weeks, no response from the other forums, I tried to compute a simple model for a greenhouse in a garden. First idea was to compute mass transfer, Navier-Stokes and heat equation all together but in my knowledge no analytical solution exists. I need to build a...
  21. B

    I Time for a cold volume of air to reach a higher air temperature

    I have a cube with a volume of 1000m3 at an initial temp of 290K. The bottom side (10m by 10m) is open to the ambient air. I put this cube into a huge fridge and cool the whole volume by 5K. I close the open side by placing a cover on it. This cube has now got a volume of air at a temperature of...
  22. SamuuLau

    I The effect of temperature on the damping of a guitar string

    I am a high school student and recently I have been working on a project about how temperature affects the frequency of a string emits. I have read blogs like https://www.physicsforums.com/threads/tension-and-frequency-with-change-in-temperature.833185/ and completed the part of thermal...
  23. kamui1

    Solving for degeneracy electron cloud temperature

    When I try P_rel_e = P_ideal I couldn't get a single number that is close to the given T_Max. It might be that I used the wrong equations but I am not sure. Can anyone give me some guidence on this question?
  24. T

    I Microwave background radiation - temperature at recombination

    The commonly called value of the temperature at recombination is 3000 K. According to this reference the process of recombination can be described by the Saha equation: 3.1. Recombination and the formation of the CMB Recombination happens quickly (i.e., in much less than a Hubble time t ~...
  25. dorothy

    Temperature & Gas: Correct or Incorrect?

    (1) Incorrect, since the root mean square speed(c^2)is directly proportional to the temperature, but it will just affect the average kinetic energy, doubling the k.e., but not related to the potential energy. (2) Correct, since the volume of gas is directly proportional to the temperature (3)...
  26. V

    Why is temperature constant after gas has expanded?

    The answer given for part (c) in the back is that temperature doesn't change as the gas in cylinder A expands to fill cylinder B. The thermodynamic system here is composed of the two cylinders A and B joined by some pipe. But, I cannot find a satisfactory explanation for temperature...
  27. S

    Why does a lower evaporator airflow cause a lower low-pressure-side saturation temperature in an air conditioner?

    The other day I read on a website that a lower evaporator airflow causes lower low pressure side saturation temperatures and higher delta T on an air-conditioner. Now I think I know why a lower evaporator airflow would cause a high delta T. If there is less air moving over the evaporator, the...
  28. Alexey_H

    Heat loss from the temperature difference

    Hello, My house has some heat loss. As an example I know the outside door temperature. How can I calculate the heat loss delta if I reduce the door temperature by 1 degree? I know that there is a formula to calculate a heat loss based on the U-value of a fabric. But I can't get those values...
  29. Rezex124

    Experiment - how temperature changes along a tube, using heaters

    TL;DR Summary: Help needed with plotting heat maps, using data we gathered in an experiment. Hello, so I'm having problems with analysing data, which we gathered from an experiment we did in class. This is meant as a type of non-guided experiments class, where we are just given an initial...
  30. Z

    A Temperature of HII Gas: Intuitive Explanation

    I have a question about the temperature of HII gas. According to Table 1.3 in Draine's book (physics of the interstellar and intergalactic medium) this temperature is T~10^4 K. I get a similar value by using the Saha equation for a hydrogen gas. However, a naive estimate of the same temperature...
  31. T

    I Temperature change due to mixing liquids, heating and heat losses

    Hello, I am stuck how to proceed with the equations below. The problem: A tank containing ##m_0## mass, with a temperature of ##T_0##, is to be filled with a total mass of ##m_1##, with the constant mass flow rate ##G## and temperature ##T_1## during ##t_p## seconds. ##T_0>T_1##. Other than the...
  32. LCSphysicist

    Diatomic molecule at a constant temperature

    A diatomic molecule ##D_{2}## in ##30K##, in ##t=0##, is in the state ##| \psi (0) \rangle = \frac{1}{\sqrt{26}}(3 | 1,1 \rangle + 4| 7,3 \rangle + | 7,1 \rangle )##, where the kets denote states ##| l,m \rangle##. Use ##\frac{\hbar}{Ic4\pi}=30.4cm^{-1}##. Obtain ##| \psi (t) \rangle ## I...
  33. C

    Free expansion of Real Gases - Dieterici EoS, Change in Temperature

    I proceeded in the usual manner in which we take ##dU = 0## in the case of free expansion because there is no heat transfer in the box, as well as no work is done. We can write, taking ## U ## as the function of ##V## and ##T##, $$ dU(V,T) = \left( \dfrac{\partial U}{\partial V} \right)_T ~...
  34. G

    I Why is there no frost below a certain temperature?

    It is 21°F here this morning and no frost on anything not even car windows. I have noticed this before when it gets cold enough there is no frost. Maybe all the moisture freezes out of the air and there is no moisture to make frost? I don't know? At what temperature is there no frost?
  35. C

    What is the change in internal energy after two processes?

    So the question goes like this: find change in internal energy in process 1->2 using diagram. And offered solutions a)-400J b)400J c)600J d)800J. First I found T1 and T2 using (P*V)/T=R and got T1=24K and T2=72K. Then I found n(number of moles) using PV=nRT and got n1=1mol, n2=1mol. Then I...
  36. J

    Temperature loss along a duct

    Hello, I am looking for assistance regarding temperature losses along a length of pipe with hot air entering one. I need to know the temperature leaving the other end of the pipe. I have been able to calculate the W/m-K (in theory but stopped a i knew the answer wasnt what i needed) losses but...
  37. StanislavD

    A Experiments for temperature dependence of persistent supercurrent?

    Imagine, in a mercury ring (superconductivity below Tc=4.15 K) we establish a persistent supercurrent. Then we organize temperature cycles (T-cycles) in the cryostat, from 3 K to 2.5 K and back. According to the BCS theory of superconductivity, the pair density decreases at warming, i.e. a not...
  38. S

    B High Temperature in Gravitational Fields: Exploring the Possibility?

    Sir, heat is proportional to the vibration of atoms. If the vibration of atom is restricted to large extent due to intense gravitational field but has high quantity of total energy in the atom then does it mean it has high tempearture like the stars?
  39. J

    I Trying to better understand temperature and entropy

    If you were to condense all the energy in the universe into a point, wouldn't the temperature be very high, yet the entropy be very low? Also if you were to spread out all of the energy in the universe, wouldn't the temperature be near zero and the entropy be very high? And this makes entropy...
  40. Algr

    Highest useful Fahrenheit temperature?

    I was watching a video about energy storage, and the subject was stuff that was around 1500° celsius, and for the whole video the graphics kept including Fahrenheit equivalents. Now I use Fahrenheit when checking the weather outside. But that doesn't make 2732F° any more relatable a...
  41. K

    I Questions about Curie Temperature Characteristics

    Is the curie temperature of a ferromagnetic material constant? Are there any factors that will raise it or lower it? For instance, what happens if my piece of iron is already in a strong magnetic field? Is the curie temperate higher, then?
  42. FEAnalyst

    Triangular cavity thermal radiation simulation

    Hi, I'm trying to solve a problem involving radiation in a triangular cavity: As you can see, lengths and emissivities of all surfaces are given. For two of them, the heat flux is known and the temperature has to be found while for the remaining surface it's the other way around. I have the...
  43. Astronuc

    High Temperature and Very High Temperature Materials

    A family member shared an article about thermovoltaics being developed at MIT with support from National Renewable Energy Lab (NREL). A new heat engine with no moving parts is as efficient as a steam turbine https://news.mit.edu/2022/thermal-heat-engine-0413 The article mentions that the...
  44. T

    Gas law problem (changing volume, temperature and pressure)

    I can’t quite work my head around this question, I am having a difficult time analyzing the question, I can’t seem to make out what the initial and final conditions are would appreciate all the help I could get cheers
  45. nuclearsneke

    Exceeding the saturation temperature of coolant on the clad for PWR

    Hello there. I have been conducting a thermal calculation of a fuel assembly for KLT-40S reactor (a small modular PWR-like reactor installed at the floating nuclear power plant "Akademik Lomonosov" with electric power of 35 MWe.) and obtained some interesting results. It seems that cladding...
  46. L

    Finding both temperature and the amount of gas added

    The volume of the cylinder is ##V=\pi r^2 h=\frac{7\pi}{250}\ m^3## the number of moles is ##n=\frac{15}{16}\ mol## so from ##PV=nRT## we get ##P=\frac{nRT}{V}=25975.5\ Pa##. Now, for the second question, it should be an isochoric process so ##V_2=V_1## and ##P_2=P_1+0.8P_1=\frac{9}{5}P_1## and...
  47. Zakariya

    Changing the Temperature in an MCNP code

    Hello everybody. I would like to ask a question; if I change the dimensions and densities and the material number identifier ZAID to a specific temperature. Does MCNP change automatically the volume of the cells? or I have to change the volume of each cell manually and indicate it in the cell...
  48. C

    I Wave in phonon as "forward and backward" movement vs temperature

    My first question here, so maybe not adequate or in the wrong topic, excuse me. I try to understand vibrating light harvesting antenna in biochemistry but it is a question of physics. We talk about a molecule with an emission spectra peak of about 650 nm. In classical physics electrostatic and...
  49. SherLOCKed

    I Will the upcoming experiment PICO measure kSZ temperature anisotropy?

    I know for sure PICO will be measuring polarization anisotropies with high fidelity. In addition, the PICO science paper shows that it will make full-sky Compton-y maps but the plots are mostly limited to l=1000. Will PICO be able to measure kSZ temperature anisotropy at l=3000?
  50. L

    Finding equilibrium temperature when there are phase changes

    If there weren't phase changes occurring I know that the temperature equilibrium would be ##T_e=\frac{m_{ice}c_{ice}T_{ice}+m_{w}c_{w}T_{w}}{m_{ice}c_{ice}+m_{w}c_{w}}##. Now, by repeating the reasoning to get the above formula (##\sum \Delta Q=0##) and adding the phase changes of the water...