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. Alfreds9

    Calculating air pressure from altitude, RH and temperature?

    Homework Statement [/B] This is a practical problem, no homework question. I'd like to determine pressure (and O2 partial pressure) at altitude, yet following a more realistic real-world calc including measured data like relative humidity (RH) and temperature at that altitude, yet all I can...
  2. Salvador

    Temperature dependant resistor for MAF

    Hi folks, so here's my recent problem, My car has a broken MAF (mass airflow sensor) the semiconductor innards are ok but the very thin metal strip that comes into the airflow tube has become brittle from old age and broken up. I know the MAF works when it sends a low voltage through the...
  3. campeola46

    Finding n and p of semiconductor given temp, NA, ND, and Ni

    I'm doing independent study on semiconductors to prepare for a future class and I'm having problems with some problems that concern finding the n and p of doped Silicon given only a temperature, NA, ND, and Ni. I understand that n*p=Ni^2, but, given that this means that n does not equal ND (and...
  4. jormi

    I Small temperature dependence in diamagnetic material

    Hi everybody! I´m chemist doing new materials and my understanding of physics is quite basic. I have a sample (single phase) of Ba and Ge and it shows diamagnetism in the magnetic susceptibility measurement, however it show a small temperature dependent behavior. As far as I understand...
  5. M

    Why Is the Calculated Temperature of the Universe Different from 3K?

    Homework Statement Two scientists detected the cosmic microwave background radiation at a frequency of 160 GHz. What is the temperature of the universe? Homework Equations peak wavelength x temperature = 2.898 x 10^-3 c = f x wavelength The Attempt at a Solution I calculated the wavelength of...
  6. Schwarzschild90

    Canonical partition function for N ideal gasses

    Homework Statement Exercise 4 in the upload titled Dok1.pdf. Write down an expression for the canonical partition function for N ideal Na2 gas molecules, when the rotational contribution is treated classically, and all inner degrees of freedom are treated quantum mechanically. Use this and...
  7. L

    Finding 2D Fermion Gas U/N with Temperature & Area

    Homework Statement For a gas of N fermions with mass M in 2D in a region of area A in thermal equilibrium at temperature T, we are asked to find ##U/N## in fuction of ##T## and ##a=A/N##. The attempt at a solution I used ##U=\sum(<n_i>\epsilon_i) = \sum(\exp(\beta(\mu-\epsilon_i))\epsilon_i...
  8. GW150914

    I Why do we need "planetary equilibrium temperature"?

    I mean, currently it seems that scientists are using equilibrium temperature of exoplanets (calculated assuming an Earth-like albedo) to determine whether a planet is habitable or not. But aren't there other more accurate ways to determine surface temperatures of exoplanets? I learned Wien's...
  9. P

    How to measure the temperature of liquid in sealed container

    I am not a scientist or particularly good with math or formulas. I have been curious about this for a while, and would appreciate anyone clarifying/correcting me. I have a stainless steel container that can be heated up to 75 degrees celcius/165 degrees Fahrenheit in a bain marie. It can hold...
  10. astrotizio

    A Stellar photosphere temperatures

    Hi all, Star surface temperature determines the occurrence of photosphere, where radiation can escape from star interior due to diminishing gas ionization and radiation absorption. If it was true the star photospheres should have the same temperature and Herzsprung-Russell diagram should be...
  11. striogi

    Writing: Input Wanted The temperature at which flesh burns

    I'm putting together an idea about a weapon (insert hand-wavy science here) that fires extremely high temperatures a very short range (100 feet or so). A Heat Shotgun, if you will. The idea is that this weapon, with a single blast, could turn the majority of a human sized creature to literal...
  12. P

    Fermi Function at High Temperature

    Hello, A question I can't seem to find a simple answer to is, what happens to the Fermi-Dirac distribution at T grows large? Mathematics suggests that it approaches 1/2, like it does when the energy becomes equal to the Fermi energy. Or, are we not allowed to use the F-D distribution for high...
  13. T

    Adsorption and Critical Temperature

    Homework Statement An extract form my textbook: " In general, easily liquefiable gases( ie. with higher critical temperature) are readily adsorbed as van der walls forces are stronger near the critical temperature. Hence 1g of activated charcoal adsorbs more SO2( Tc=630K),than CH4...
  14. Asafish

    How much heat required to raise the temperature of potassium

    Homework Statement At low temperatures, the specific heats of metals is described by the expression ## c=kT + AT^3 ## , where k and A are constants. Here the first term describes the contribution of free electrons and the second the lattice contribution. How much heat is required to raise the...
  15. L

    Is temperature measured in kWh normally distributed over different time spans?

    Are the temperature over 24 hours normally distributed? Over 1 year? Over 15 years? Is there a difference in distribution depending on the time span Are MIN temperatures per day i.e. the coldest temperature measured over a 24hr period normally distributed? Over one month Over one year Over 15...
  16. S

    Calculating the output temperature of a Solar Thermal system

    So say I have a PV-Thermal array and assuming standard test conditions. How would I calculate the temperature of the water coming out of the system? The thermal output of the system is 67.5kWp with a maximum flow rate of 65L/h. Approximately 500m of 3/4" pipes.
  17. S

    What is temperature stability? (Lamination)

    I'm doing some work on solar and I'm reading about properties of lamination materials, particularly EVA lamination. Anyway, one of it's properties is 'temperature stability' but I can't find a clear definition of what this means. EVA lamination is sandwiched in between a solar cell, so I can...
  18. Gerald Kaiser

    Are temperature and pressure related by relativity?

    Since the temperature of a gas is related to its average molecular energy and the pressure to the average molecular momentum, it would seem that a Lorentz transformation would somehow relate the two. Does anyone know of related work?
  19. L

    Can power supplies cause temperature fluctuations....

    can power supplies cause temperature fluctuations in a circuit? Or, instead, are they sensitive to temperature fluctuations in the environment, which can cause temperature fluctuations in a circuit?
  20. KishoreAM

    Temperature Profile -- temperature-length curve of a metal bar

    Guys... If there is a bar, half of it is Copper and another half is Steel (Length wise) and both of its ends are at 1000K and I want to know how to find the temperature- length curve. this was an interview Question by the way.
  21. Elvira

    Calculate the temperature based on Resistance

    Hello experts... I have an experiment pool boiling. The test section filled with DI water, and use thin flat copper as the heater that connected to the power supply. I want to ask how to measure or calculate the heater temperature if I only have the resistance, voltage and current data reading...
  22. M

    Temperature & kinetic energy of particles in solid vs gas

    Consider the internal energy of a gas and solid (different materials) both at the same temperature, which material has the larger potential energy and why? Do they also both have the same kinetic energy? Finally is the definition of temperature as the average kinetic energy of the particles only...
  23. amrmohammed

    Logarithmic mean temperature difference for heat transfer

    Homework Statement [Update: just realized that the LMTD is a temperature difference, so my question was not valid] :P Calculate the logarithmic mean temperature difference (LMTD) to heat water flowing through a tube from 21 C (Ti) to 40 C (Te) if the tube has a fixed temperature of 45 C (Ts)...
  24. Liam A

    I Understanding the Polar and Equatorial Temperature Differences on Planets

    on earth, we have the poles being very cold and mostly frozen, while the equator is very warm and humid. i would like to know specifically what causes this. i know it is partially because of their exposure to the sun, but i'd like to know some of the details and factors involved. i'd also like...
  25. S

    Current in a solar cell when temperature increases?

    What happens to current in a solar cell when temperature increases? I found two sources with different information. 1) As solar panel temperature increases, its output current increases exponentially while the voltage output is reduced linearly.' 2) Whereas, this second website says short...
  26. S

    Pressure and Temperature Dependent Dynamic Air Viscosity

    Hello, I am currently working on a project which involves compressing air at high pressures and temperatures. I spent hours having a look for a pressure and temperature dependent equation for the dynamic viscosity of air but the only ones I could find were all temperature dependent only, such...
  27. J

    Calculate the temperature for this reaction to occur

    1. Homework Statement Homework Equations KE = 3/2 R/NA T The Attempt at a Solution By using the formula above, I used 2.4 x 10^-14 J as the mean translational KE , but it should be 1.2x10^-14 , why? I thought the mixture contains both deuterium nucleus and the proton? Why half KE of mixture?
  28. C

    Temperature dependence of the index of refraction of air

    The index of refraction for a gas depends on temperature, as well as pressure. What is an experiment that would determine the temperature dependence of the index of refraction of air?
  29. T

    Temperature after mixing ice and water

    Homework Statement 5 g of water at 30°C and 5 g of ice at -20°C are mixed together in a calorimeter Find the final temperature of the mixture. Water equivalent of the calorimeter is negligible,specific heat of ice=0.5 cal/g°C and latent heat of ice =80 cal/g. Homework Equations...
  30. poot lovato

    Can the temperature of an object be derived from the EM Wave

    Can the temperature of an object be derived from the EM Waves it emits? I know that everything having a temperature over absolute zero emits thermal radiations. The hotter the object gets, the higher the frequency of the wave goes. But for example if I have a hammer which emits a wave xHz...
  31. T

    I left a soda in the car and it still feels cold.

    After a cookout on Saturday, I left two cans of Coca-Cola in my bag. Around Monday morning which is almost two days later, when I left for school, the cans were still cold with moisture on it. The next day, I put another can of Coca-Cola in the car and only left it overnight to see what the...
  32. C

    Pressure and temperature -- the effects of one upon the other

    Greetings, I get that increased temperature increases pressure. But does increased pressure increase temperature. For example: 1) If I press down on a table with a heavy object, does it increase its temperature. 2) Or does the pressure of the crust and the mantle of the Earth, contribute...
  33. Doktor Mabuse

    Temperature at which pea protein is destroyed?

    I am taking a protein supplement that has far too much sodium in it. If I took the amount I need every day, I would far surpass the safe upper limit of daily sodium intake. I had the idea of dissolving the pea protein powder in water, filtering out the sodium, and then evaporating the water...
  34. G

    Inverse Square Law, Temperature Change, and Heat Source Temp

    I've been trying to wrap my head around the relationship between temperature increase of an object at a distance and temperature of a heat source. From what I've found, the temperature increase of an object from thermal radiation is affected by the inverse square law...
  35. M

    Temperature rise due to cycle test

    Hello all, I am working on a few test scripts to test the life of a hydraulic cylinder. (It is a mechanically operated cylinder and has a positive displacement) The testing will involve thousands of continuous pump and retraction operations, due to which the temperature of the piston seal and...
  36. T

    How to calculate the size of a star with just temperature

    Homework Statement This isn't a specific problem, but my professor told us that we can calculate the size of a star if we know the temperature of it. Homework Equations Stefan-Boltzmann Law, Wien's displacement law. The Attempt at a Solution With the temperature i can also get the intensity...
  37. E

    Calculating Temperature at a Distance from Heat Source

    Is there a formula or equation to find out how heated a place x meters/kilometers from a heat source will be, if we have the size of the heat source, it's shape, it's surface temperature, it's inner temperature, everything? + the distance between source of heat and the specific location is...
  38. Y

    Temperature of boiling surface

    What determines the surface temperature inside a pot of boiling water, right over the heat source? Can it go much over boiling temp if the water's just gently boiling?
  39. DevonZA

    Mean temperature of winding when current falls

    Homework Statement Homework Equations R2=R1(1+alpha(t2-t1)) The Attempt at a Solution R1=250/5=50ohms R2=250/3.91=63.94ohms R2=R1(1+alpha15degrees(t2-t1)) 63.94=50(1+1/254.5(t2-15)) t2= Now I found this online but the answers provided still don't match, 84.25 being the closest. When...
  40. MaxKang

    I Can you have a high temperature with very little heat?

    From what I know, temperature is defined to be the average kinetic energy of molecules within a system while heat is said to be the total kinetic energy of molecules. I know this might be something we can never achieve in real life but here's how my thought process went. Imagine you have a box...
  41. G

    Kelvin thermodynamics temperature scale

    The thermal efficiency of a reversible heat engine is solely a function of the temperature of the two reservoirs. η = f(θH,θC) = 1 - (QC/QH) (QC/QH) = 1 - f(θH,θC) (QC/QH) = Ψ(θH,θC) The simplest function that can be used is T1/T2 (QC/QH) = T1/T2 In order to define the Kelvin scale we assign a...
  42. r_prieto5

    Safety factor, temperature and torque

    Homework Statement https://drive.google.com/file/d/0BxPEJS0qVOpeWENSREI1RlNsNDQ/view?usp=sharing A hub is connected to a shaft with a shrink fit (pressurized oil assembly, grease removed). The material of the hub is quenched and tempered steel (ReH = 450 N/mm2) and the material of the shaft...
  43. OrangeDog

    Estimating drag using only a temperature profile

    I was reading this thread on Reddit about estimating drag using only a temperature profile. I was reading the responses, and I feel like most of them are missing something. Since this forum is more science-focused, what do you guys think...
  44. lfqm

    I Temperature in quantum systems

    Hi! These days I've been studying thermodynamics of quantum systems, and in so a very basic doubt come to me... I hope you guys can help me: When we study the usual hamiltonians of quantum mechanics (H-atom, harmonic oscillator, etc.)... Are these hamiltonians modeling the system at...
  45. T

    Why should a heat pump receive low return temperature?

    One is always told that a heat pump (heating water) should receive return water with a temperature as low as possible. I've never really understood why. My initial thought is that if the return is higher, then it's "easier" for the heat pump to heat the water up to whatever supply temperature...
  46. jfulky

    Finding Increase in Temperature for Two Rods

    Homework Statement A steel rod and an aluminum rod of equal length and diameter are placed end to end and secured so that they cannot flex. The rods are heated to the same final temperature, and the steel is found to increase in length by one-tenth of a percent. If the total length of the rods...
  47. Alfreds9

    Water evaporation, temperature, wind and heat capacity?

    Hi, I'd like to know how I'd put together, either elegantly or at least in physical terms, that surely water evaporation in a large pool of V volume and S surface is influenced by wind (increased by it as opposed to having side barriers), temperature (increased by direct sunlight as opposed to...
  48. C

    Rate body temperature increases given rate of heat transfer?

    Homework Statement Suppose you walk into a sauna that has an ambient temperature of 57.0°C. Calculate the rate of heat transfer to you by radiation given your skin temperature is 37.0°C, the emissivity of skin is 0.95, and the surface area of your body is 1.60 m2. I solved this first part and...
  49. R

    Effective annealing parameters in N-doped Zinc oxide

    Good day every one! Based on my research as you increased the temperature, the grain size become bigger and the thickness decreased, but in some paper, thickness increased. The effects of annealing temperature is almost the same to the temperature. But if you will considering doping for...
  50. TeethWhitener

    B Hawking radiation / String Hagedorn temperature?

    I was playing around with numbers and found that the equivalent temperature for Hawking radiation from a Planck mass black hole is ~5×1030 K. Later, I saw that the Hagedorn temperature for strings (where the partition function is expected to diverge) is reported to be around ~1030 K. I thought...
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