What is Kelvin: Definition and 90 Discussions

The kelvin is the base unit of temperature in the International System of Units (SI), having the unit symbol K. It is named after the Belfast-born Glasgow University engineer and physicist William Thomson, 1st Baron Kelvin (1824–1907).
The kelvin is now defined by fixing the numerical value of the Boltzmann constant k to 1.380 649×10−23 J⋅K−1. Hence, one kelvin is equal to a change in the thermodynamic temperature T that results in a change of thermal energy kT by 1.380 649×10−23 J.The Kelvin scale fulfills Thomson's requirements as an absolute thermodynamic temperature scale. It uses absolute zero as its null point (i.e. low entropy). The relation between kelvin and celsius scales is TK = t°C + 273.15. On the Kelvin scale, pure water freezes at 273.15 K, and it boils at 373.15 K.
Unlike the degree Fahrenheit and degree Celsius, the kelvin is not referred to or written as a degree. The kelvin is the primary unit of temperature measurement for the physical sciences, but is often used in conjunction with the degree Celsius, which has the same magnitude.

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  1. J

    I Measurement of heat as an interval measurement or a ratio measurement

    Hello! I am new to this forum and I'm not even sure if this is the right place to ask but here goes: I am studying Research Methods. I got to the part where the teacher is teaching us about levels of measurement. They said that there are a few levels but the two that are significant to my...
  2. gary808

    I Mercury as a plasma at 150 Kelvin

    I was reading up on a theoretical engine employing the following, “Mercury plasma pressurized at 250k atmospheres, at a temperature of 150 degrees kelvin (-123° C), and swirled within its accelerator to 50k RPM.” Does pressurizing mercury so much somehow allow a plasma to form at such sub-zero...
  3. nomadreid

    I Quantum effects near 0 Kelvin

    In https://phys.org/news/2016-09-cold-black-holes.html it is stated that a supermassive black hole interior could be 10^-14 degrees Kelvin. Is there a limit, perhaps due to quantum effects, below which a temperature (in a black hole or elsewhere) can go? Or do the possibilities approach 0...
  4. AN630078

    Why do we not need to convert from degrees Celsius to Kelvin?

    I understand that the Kelvin scale begins at absolute zero and that the Kelvin scale may even be referred to as the absolute scale. As the units begin from a definite zero and increase with equal amounts of energy being added to the particles of the substance being measured (at equal intervals...
  5. Piotrovskiy Yury

    B Kelvin - not the basic, but the derived unit of measurement?

    1. Kelvin - not the basic, but the derived unit of measurement? Modern physics believes that kelvin is the basic unit of measurement of SI (one of seven). At the same time, in all encyclopedias and textbooks it is written: T= Θ/k = Θ /1,380649x10е-23 Θ - is the energy of the molecule in...
  6. F

    What is the Entropy at ZERO Degrees Kelvin?

    Planck states that all perfect crystalline system have the same entropy in limit T approaches zero,so we can put the entropy equal zero.Can we demonstrate that or is it only a presumption?
  7. T

    Adiabatic PVT relationships - why Kelvin and not Celsius?

    Homework Statement Here's a derivation of the adiabatic PVT relationships. QUESTION: When solving adiabatic PVT homework problems I found that I needed to express temperature in Kelvin, rather than Celsius, to get the right answers. Where in this derivation should this be specified, and how...
  8. Mohammed Sayanvala

    What do wave crests indicate about a boat's speed?

    Homework Statement *I cannot place the original image due to copyright reasons, but the image above is a good alternative. "Wave crests spread out behind a boat as shown above. What do the wave crests indicate about the boat's speed?" It is increasing. It is less than the speed of the water...
  9. S

    B Is 3-point of H20 used for Kelvin a certain set of isotope

    If I had had enough space to enter the proper question, it would have been: Is the triple point of water which is used for the definition of the unit of Kelvin defined as water having a certain isotopes such as 2 Hydrogen-1 & 1 Oxygen-16? Or would the error introduced by using different...
  10. J

    B When Difference between Kelvin and Celsius are negligible

    This question is more for practicality than anything else, and I realize it may be partly subjective. At what temperatures can the 273 degree difference between Kelvin and Celsius scales be ignored? I'm thinking for examples regarding stars and very high temperatures. Surely once you get to 15...
  11. C

    I Negative Kelvin? How Is It Possible?

    Negative Kelvin http://science.sciencemag.org/content/339/6115/52. How is this possible? If anyone could help me understand this I'd appreciate it.
  12. Vivek098

    Kelvin and Platinum Temperature Scale.

    Is it possible that Kelvin and Platinum Temperature Scale give same reading of Temperature?
  13. C

    I Exploring Negative Kelvin: Is It Possible?

    I recently saw an article that talked about negative Kelvin. How's this possible?
  14. Ben70

    I What would happen if you brought a deodorant can to 0 Kelvin

    Not an experience physicist but just curious as to what would happen.
  15. Lafith

    Measure Entropy: Can Absolute Entropy be Zero?

    Can we measure 'absolute entropy' of a system. Also can entropy become zero at 0 kelvin.is it possible only theoretically?
  16. S

    A Kelvin Units: Help Understand Optics of Graphene

    Hey! In https://www.researchgate.net/publication/230937856_Optical_properties_of_graphene [Broken] article (Optical properties of graphene) I found out the frequency is expressed in Kelvins. Could you help me with it - how did the author do this unit transformation? Thanks in advance!
  17. MathematicalPhysicist

    A question on absolute kelvin temperature scale.

    I was asked in an exam the following question: Q: How is the absolute Kelvin Thermodynamic temperature scale defined ? My answer is the following: A: The absolute zero kelvin thermodynamic temperature is defined as the temperature for which the entropy of the system is zero, i.e ##S|_{T=0} =...
  18. ATY

    Kelvin Waves: How Do They Work and Why Do They Move Along the Coast?

    can somebody explain to me how kelvin waves are working ? I just found, that the waves move along the coast due to the coriolis force, but I have no clue why this is happening.
  19. P

    Difference between using temperature in Celsius and Kelvin

    For one my homework questions I was asked to find the specific heat capacitance of a certain material. The specific heat capacitance has a temperature dependence given by: c = 0.20 + 0.14T + 0.023T2 the units for T is temperature in Celsius and c is measured in cal/gK. 2.0 g of the material was...
  20. 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...
  21. F

    Celsius to Kelvin conversion problem (Kinetic theory)

    Homework Statement Find the temperature T that allows the rms speed of a gas to be equal to another gas with T=47°C. The molecular mass of the first gas is 64, and the molecular mass of the second gas is 32. Homework Equations v_{rms}= \sqrt{\frac{3RT}{M}} The Attempt at a Solution The...
  22. wavepax

    Superconducting Resonator matches 3 Degree Kelvin Spectrum

    Carver Mead writes in his book, "Collective Electrodynamics", that experimental evidence indicates a superconducting ring and capacitor resonator circuit will increase from zero voltage (scalar potential difference) to an energy matching a 3 degree Kelvin black body radiation spectrum...
  23. N

    Calculating Fire Temperature from Thermal Energy

    is there a way to calculate the themperture of something like a fire, if you know the thermal energy it produces.
  24. weezy

    Possible violation of the Kelvin statement (2nd law)?

    Say I have an infinite cylinder filled with monoatomic gas and on one end has a piston attached to it. I now supply heat to the cylinder. The gas expands thereby converting all of heat energy into physical work(displacement of the piston). Since the cylinder is very long it eliminates the...
  25. P

    Circulation Around an Airfoil and Starting Vortex

    Homework Statement Using Kelvin’s circulation theorem, find the qualitative and quantitative relation between the circulation around an airfoil and the circulation of the starting vortex. Homework Equations Kelvin's circulation theorem: DΓ/Dt=0 The Attempt at a Solution I don't really know...
  26. J

    Energy unit to kelvin, seconds, density, length

    Homework Statement Convert 1 ##Gev## to Kelvin, and convert ##GeV^{-1}## to meters, seconds, and convert ##GeV^4## to density ##(kg/ m^3).## Homework Equations natural units ##c=h=k_B=1## The Attempt at a Solution I know to convert energy to meters, I can use ##\lambda =hc/E##, I get the...
  27. klotza

    Insights Explosion-Generated Collapsing Vacuum Bubbles Reach 20K Kelvin - Comments

    klotza submitted a new PF Insights post Explosion-Generated Collapsing Vacuum Bubbles Reach 20,000 Kelvin Continue reading the Original PF Insights Post.
  28. S

    Exploring Cascade Cryogenics: From Methylene Chloride to Liquefied Air at 70K

    http://www.pbs.org/wgbh/nova/physics/reaching-ultra-low-temperatures.html is this thing accurate? It uses methylene chloride as first refrigerant, then ethene, and then oxygen, and gets to liquefy air...down to 70kelvins after researching the very small info on the net about cascade...
  29. Questions554

    Why is the conversion from eV to Kelvin so high?

    I mean eV are something like 1.6x 10^-19 joules but somehow 7eV corresponds to 81121 K?? At that temperature you should have a lot more energy than 7eV! No?
  30. CheesyPeeps

    Kelvin Scale Accuracy: Why 1K = 1°C?

    Why is the Kelvin scale more accurate than the Celsius scale when a change of 1K is equal to a change of 1°C? It's something I've always wondered about but never looked into. (Apologies if the answer is incredibly simple. I'm still very new to the world of physics :smile:)
  31. gracy

    Celsius to Kelvin Conversion: Solving for T2

    Homework Statement At constant volume and number of moles T1/T2=P1/P2 As per ideal gas equation So given data is T1=27 degree celcius P1=80 Cm ,P2=120 Cm T2=? Homework Equations T2=P2/P1 multiplied T1 The Attempt at a Solution :120 cm/80cm multiplied by 27 degree celcius =40.5 degree...
  32. shmijda

    TRUE/FALSE light question

    Homework Statement If a black blob and a white blob of the same size are each heated to 3000 Kelvin, the black blob will glow brighter.Question 11 options: True False Homework Equations none The Attempt at a Solution white because it reflects all incident rays?
  33. M

    Schools Thesis in search of university, regarding Carnot and Kelvin

    Greetings, A Thesis regarding the historical accuracy of portrayal Sadi Carnot and Lord Kelvin's work seeks a University. It is based largely on the images below (note highlighted areas), taken from their original work. As you know, Sadi Carnot and Lord Kelvin are the fathers of the science of...
  34. kelvin490

    Gas close to zero Kelvin

    Consider an adiabatic expansion of an ideal gas that work is done against friction or a piston. Since no heat exchange can occur the gas keep on losing energy and its temperature decreases and the gas molecules getting further and further apart. In principle the temperature can get down to a few...
  35. P

    Rigorous Definition of Kelvin?

    Hi all, I'm reading through Zwiebach's String Theory text on my own and am thinking about one of his very elementary exercises on "units." We are asked to define temperature in Kelvin with reference to the fundamental units of mass, length, and time. My thought is the following: We take...
  36. G

    Find Thermal Diffusivity from Kelvin Functions

    Homework Statement I performed an experiment where we have to find the thermal diffusivity of rubber. This is done using the phase difference of the axial and external temperatures of the rubber. The teacher's guide says to use the Kelvin functions, plot them against x. Where x = r(√(2pi/TD))...
  37. R

    Has anything in the universe ever reached 0 Kelvin?

    I was just wondering, has anything in the universe ever reached 0 Kelvin? Is it even possible for particles and sub atomic particles to completely stop moving within an object? If so, what happens then? I heard things start to get "weird" Also, would reaching the famous "absolute zero" result...
  38. Hyo X

    Applied bias at Zero Kelvin?

    Hypothetically: A pair of electrodes with a small insulating barrier between them. Transport is via tunneling through the barrier. You apply a small bias, and measure conductance because there is tunneling current. At 0 K, can there still be tunneling? Is it possible for a tunnel junction...
  39. Hyo X

    Electron behavior at 0 Kelvin

    What happens to electrons at 0 Kelvin? I know in theory all atomic motion stops (vibrational energy = 0), and that the electrons occupy the lowest energy levels. But it seems the electrons would have to still be orbiting or occupying non-localized states, and thus have kinetic energy? Can...
  40. V

    Small non-magnetic motors that work at temperature of 4 Kelvin

    Does somebody knows which companies produce small (approx. matchbox-sized) motors that can work at temperature of 4 Kelvin and are nonmagnetic ? For example like this one: http://www.attocube.com/nanoPOSITIONING/ANPx341/ANPx341.html [Broken]
  41. S

    Conductivity of metals at 0 kelvin?

    What is the conductivity of metals at 0 kelvin? i think it will be zero because at 0 k entropy is zero. Every motion is cease.
  42. S

    Comparing Kelvin and Celsius Temperatures in a Rigid Container

    If you heat the air inside a rigid, sealed container until its Kelvin temperature doubles, the air pressure in the container will also double. Is the same thing true if you double the Celsius temperature of the air in the container? I don't think so, because pressure is directly proportional...
  43. X

    Negative Kelvin temperature? (Recent Science paper)

    Chemistry student saying hi to everyone Just read http://www.nature.com/news/quantum-gas-goes-below-absolute-zero-1.12146 about negative temperature. I knew I wouldn't understand a single sentence of the actual Science paper, but I took a look at the Science perspective (Lincoln D. Carr) but...
  44. J

    Why mole and kelvin are basic units?

    Mole is just a number. It doesn't really measure anything so why is it a fundamental unit? And with kelvin - it represents the average energy of the atoms/molecules in a compound. Why is it a fundamental unit? Temperature can easily be represented in joules.
  45. A

    Million Kelvin gas clouds? Really?

    Just read an article on the internet that a giant baryonic cloud surrounds the milky way with a temperature of 1 - 2.5 million Kelvin. http://iopscience.iop.org/2041-8205/756/1/L8?fromSearchPage=true Now my question is this: how on Earth is it possible for such a cloud to stay that hot...
  46. N

    273 + degree Celsius = Kelvin Why 273?

    Temperature conversion: 273 + degree Celsius = Kelvin Actually why is that 273? How does one come up with this? My teacher mentioned gann's law(not sure if this is the one) but i couldn't find anything related to this, which law should it be? Thanks in advance.
  47. R

    Kelvin water dropper generator

    I have only recently found out about this idea (many thanks m.e.t.a.) and I am curious about it. Could it be used to produce electricity on a mass scale, and if not, why not? Is the efficiency of conversion from gravitational potential energy into electric potential energy less that the...
  48. S

    Exploring Matter at Zero Kelvin: Can it Exist as a Gas?

    Hello All, Can matter exist in a gaseous form at zero K? I am asking because common gasses (e.g. air) would liquify at cryogenic temperatures... Many thanks
  49. C

    Free electrons at zero kelvin?

    At zero kelvin,are there free electrons? At zero kelvin,the free electrons should have ZERO energy.But they are able to move under the influence of a electric field? But when they are attracted towards the positive potential shouldn't they gain K.E? So they are moving at zero kelvin?
  50. G

    The temperature change of an ideal gas, Joule Kelvin expansion (const. enthelpy)

    Homework Statement This is the last part of the question. So far have been made to derive: ## \mu _{\text{JK}}=\left(\frac{\partial T}{\partial P}\right)_H=-\frac{1}{C_P}\left(\frac{\partial H}{\partial P}\right)_T ## Then ##\left(\frac{\partial H}{\partial P}\right)_T=V - T...