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.

View More On Wikipedia.org
Recent contents Top users
  1. A

    Chemicals that freeze at less than 60 Kelvin

    Does anyone know of a reference to a list of all known chemicals that freeze at less than 50 K? I know lots of organic molecules do, but I don't know which ones. I also can find the freezing points of all the elements pretty easy, but chemicals are proving more elusive.
  2. C

    What is the usage of Kelvin function?

    When I was scanning the materials of Bessel function, I found that when the variable is: xe^{\frac{3\pi}{4}i} the Bessel function is called Kelvin function. Then what is the practical appliance of this function?
  3. L

    Volumetric expansion Kelvin required?

    Volumetric expansion Kelvin required? Homework Statement Suppose that the steel gas tank in your car is completely filled when the temperature is 11.5 °C. How many gallons will spill out of the 20.9- gallon tank when the temperature rises to 37.6 °C? Homework Equations βgasoline = 950...
  4. E

    Can someone explain? (Celcius to Kelvin question)

    A sample of liquid is heated from room temperature to just below the boiling point. The overall change in temperature is 75°C. Express this temperature change in kelvins. The book has the answer as 75K. How did they arrive at that answer? I don't think I understand the problem. I rather...
  5. S

    The kelvin scale - how could it have been defined?

    Hey, I know that the kelvin scale uses the absolute zero as its null point. If so, I wonder why the scale needs to be defined using the triple point of water. I mean, the absolute zero serves the purpose of defining the kelvin scale already, doesn't it?
  6. A

    Knowledge required for a research project using Kelvin Probe

    Alright so a professor took me up for a research project which makes use of a Kelvin Probe. However I only have a year of introductory Physics under my belt (Mechanics and Waves & Oscillations). I started studying some of E&M which I assumed I needed to know, this summer but didn't get too far...
  7. B

    Is the Joule-Kelvin Expansion Reversible?

    Homework Statement Is the Joule Kelvin expansion reversible or not? Homework Equations The Attempt at a Solution It\'s definitely quasistatic but I\'m not sure if it is reversible or not? I have a feeling it\'s not but can;t explain why...any ideas?
  8. B

    Measuring Voltage with Kelvin Water Dropper: Device Options and Combos

    I ve seen some answers to this issue of measuring the voltage of a low current high voltage system such as the kelvin water dropper. We have buolt the device and it functions properly. However once we attach any kind of meters to the device it no longer sparks and no longer charges...
  9. C

    Joule kelvin expansion, thermodynamics

    Homework Statement for a jk expansion, I know dU=0. I think this is because dQ=0 as its isolated and dW = 0 as there is no work done against the surroundings. but is dW 0? does the gas do work against itself? I have also seen that the temperature change of an ideal gas = 0. how can...
  10. N

    Why some metals have 0 resistance at 0 kelvin

    Hey someone please explain why some metals have 0 resistance at 0 kelvin (absolute zero). Please explain the complete mechanism properly.
  11. G

    Kelvin water dropper and Walter Lewin

    I recently came across MIT prof. Walter Lewin's fascinating demonstration of a Kelvin water dropper, which can be seen here: https://www.youtube.com/watch?v=http://www.youtube.com/watch?v=oY1eyLEo8_A (EDIT: If your browser is like mine that didn't work, try this: ) As shown in the...
  12. A

    Difference between a kelvin and a celcius degree

    Homework Statement I feel stupid posting this but I am completely lost. This is a problem on my Chemistry textbook's website, which gives immediate feedback on whether you are right or wrong, and I am just unable to get it right. The question: What is the difference between a kelvin and a...
  13. P

    Derive an expression for the Fermi energy of a 2D structure at 0 kelvin?

    Homework Statement That's basically the whole question in the title there, ie; Derive an expression for the fermi energy of a 2d structure at 0 kelvin. 2. The attempt at a solution Basically the first part of the question had us sketching the Fermi-Dirac distribution function at 0K for...
  14. T

    Why Use Sense Resistors in 4-Wire Kelvin Measurements?

    In a 4-wire (kelvin) measuring system, why are there "sense" resistors? I understand that because there is very little current on the sense line there is no voltage drop. What purpose do they serve?
  15. P

    Theoretical Effects of Achieving Zero Kelvin in a System

    I realize this is not possible, so posting statements that it's not will be fruitless but. If were possible to achieve zero kelvin in a system what would theoretically happen? and would it also have to be universally wide or in a region completely detatched from space and time?
  16. S

    Modelling helium in the joule kelvin expansion

    How is it best to model Helium gas, Ideal gas equation? Dieterici? Van der Waals? some other equation? Also if it is dieterici or van der waals,what the values of a and b, the constants in the equation of state.
  17. E

    What makes a Kelvin Generator work?

    I am wondering how a Kelvin water dropper works and can generate sparks. Basically, water drips onto two sides, and the apparatus attracts positive charge to one side and negative charge to another side. The charge eventually builds up high enough to make a spark. You can see more information...
  18. K

    From Celsius to Kelvin - why +273?

    Hi, I am puzzled by the use of the number 273 when converting from Celsius to Kelvin and vice versa. I know that Celsius scale is based on ice point and steam point, whereas Kelvin scale is based on triple point of water, which is very very close to ice point. I am a teacher and i was...
  19. F

    Understanding the Kelvin Equation

    Hi I have problems understanding the Kelvin equation: \ln {p_v \over p_0}= {2 \sigma V_m \over rR_mT} You can rewrite Kelvin equation in the folowing form as well: p_v =p_0*exp({2 \sigma\over r}*{M \over \rho_lR_mT}) It is obvious from the above equations that p_v is always bigger...
  20. M

    Power & Engine efficiency - Using heat (kelvin)

    Homework Statement 1. Homework Statement A power plant taps steam superheated by geothermal energy to 505 K (the temperature of the hot reservoir) and uses the steam to do the work in turning the turbine of an electric generator. The steam is then converted back into water in a condenser...
  21. M

    Engine efficiency - using heat (kelvin)

    Homework Statement A power plant taps steam superheated by geothermal energy to 505 K (the temperature of the hot reservoir) and uses the steam to do the work in turning the turbine of an electric generator. The steam is then converted back into water in a condenser at 323 K (the temperature...
  22. S

    Converting Celsius to Kelvin Easy but slightly confusing

    Homework Statement I'm doing calorimetry, and I have 34.73C and 63C. I need to subtract 63 from 34.73, and get the answer in Kelvin. Homework Equations The Attempt at a Solution I know you add 273 to Celsius values to get Kelvin, but I am not sure which of these methods is correct: 1...
  23. Saladsamurai

    KELVIN scale-Can't make sense of the last step of this solution

    I do not understand how they went from \ln T_c-\lnT_H=\theta_c-\theta_H to \theta=\ln T+C Why did the subscripts drop out? What just happened?
  24. A

    Entropy of a perfect gas at 0 kelvin

    Hello, I'm still trying getting familiar with the concepts of statistical mechanics and thermodynamics , and there's this equation for S of an ideal system, which somehow perplexes me. Suppose the ideal gas is composed of N indistinguishable atoms , then : S = \frac{U - U_{0} }{T} + k Ln...
  25. S

    Kelvin & Watts: Light Penetration Explained

    Hi, I have a question regarding light, specifically artificial light. Please forgive me I am not a physics guru by any means and my terminology may be completely wrong, but hopefully someone will be able understand what I am trying to ask. First, the only way I know how to ask is in basic...
  26. D

    Kelvin Temperature - Celsius Temperature Change

    Hello, I'm going to post a curious question. Today I found a case where I have no idea what to do. I'm working with the Thermal Conductivity and it's W/(m ºC) or W/(m K) then I don't know how to change from a way to the another one because kelvin and Celsius degrees are not...
  27. S

    Testing Kelvin Planck's Second Law of Thermodynamics

    can anyone proove "kelvin plank" statement of second law of thermodynamics or atleast show that it is always followed in any cyclic process...
  28. J

    Why Must We Use Absolute Temperature for Ideal Gas Law?

    Question Why must we use absolute temperature in the ideal gas law (PV = NkT)? Why using the Celsius scale would give nonsensical results? I am not sure what is the reason, can anyone helps?
  29. M

    Understanding 1233K on the Kelvin Scale

    Does anyone know the significance of 1233 degrees Kelvin?
  30. Hans de Vries

    Superconductivity found at 175 degrees Kelvin?

    http://www.superconductors.org/news.htm http://www.superconductors.org/175k_pat.htm Regards, Hans
  31. D

    Spectral distribution of light source -> Kelvin degrees?

    Hi all, new here (from Sweden, so excuse my english). I would like to take the spectral power distribution of a light source (first and foremost different kind of flourescents, not black bodies) and calculate the kelvin temperature of the light emitted from the light source. With the help...
  32. U

    Less than 0 kelvin? Meaning of temperature

    If tempertaure means the movement of particles, Can tempertaure be below 0 Kelvin? I mean no movement, vacumm
  33. G

    Going Below 0° Kelvin: Universal Inertia?

    As there is nowhere in the Universe below 0° Kelvin. Could heat be considered a universal inconsistent medium? If we were to go below 0° Kelvin, would total inertia follow? Thanks, Glynis
  34. S

    What Should Hl Be in a Joule-Kelvin Helium Liquefier?

    We have a helium liquefier which takes compressed He gas at 14 K, liquefies a fraction alpha and rejects the rest at 14K and atmospheric pressure. I've got to the stage alpha = (Hf - Hi)/(Hf - Hl) where Hf, Hi, Hl are the final, initial and liquid enthalpies respectively. I know that the...
  35. T

    Kelvin & Joule Link: Energy Unit Relationship?

    Is there some kind of link between the units Kelvin/second and Joule/second? I'm thinking a value in Kelvin would represent an amount of energy, just as Joule. Or?
  36. K

    When are farenheit and kelvin numericaly equaly?

    15. [SFHS99 10.P.13.] At what Fahrenheit temperature are the Kelvin and Fahrenheit temperatures numerically equal? is that possible because kevlin will always be aroudn 200 greater anyway .. how do you do this
  37. R

    Exploring Atoms at 0°K: Uses & Mechanics

    1)I am very interested to know about studies being done into the uses of atoms at 0 degrees Kelvin (I understand this as the temperature at which atoms cease to oscillate?) Apparently this has possible uses as nano-computers whereby a normal object, such as a coin can house massive memory...
  38. tony873004

    Units - Watts, meters & Kelvin

    Units -- Watts, meters & Kelvin I have an equation: L = \sigma T^{4} * 4 \pi R^{2} Which I fill with values and units L=5.67*10^{-8} * (5860K)^{4} * 4 \pi * (6.96*10^{8}m)^{2} and I get an answer: 4.07*10^{26} K^{4} m^{2} The correct answer is: 4.07*10^{26} watts I don't...
  39. E

    Doppler Coefficient Values: BOL & EOL in SI & Kelvin

    I know that the typical values of Doppler coefficient over core life are about -1 *10^-5 Deltak/k/°F at BOL and -1.5 * 10^-5 Deltak/k/°F at EOL. What are the value in SI units? Are they the same, but in Kelvin? Thanks, Ken
  40. D

    Exploring the Kelvin Scale: Understanding the Absence of Negative Values

    Why the Kelvin termo scale has no negative values? I'm just asking if some one knows and is it ok and why.
Back
Top