Kelvin, definition

As can be seen in Figure 8.23, mirror images of this structure (reflected through a vertical mirror perpendicular to the plane of the page in the figure) are nonsuperposable—classic chirality by the Lord Kelvin definition, extended... 

The new international temperature scale, known as ITS-90, was adopted in September 1989. However, neither the definition of thermodynamic temperature nor the definition of the kelvin or the Celsius temperature scales has changed it is the way in which we are to realize these definitions that has changed. The changes concern the recommended thermometers to be used in different regions of the temperature scale and the list of secondary standard fixed points. The changes in temperature determined using ITS-90 from the previous IPTS-68 are always less than 0.4 K, and almost always less than 0.2 K, over the range 0-1300 K. 

The ultimate definition of thermodynamic temperature is in terms of pV (pressure X volume) in a gas thermometer extrapolated to low pressure. The kelvin (K), the unit of thermodynamic temperature, is defined by specifying the temperature of one fixed point on the scale—the triple point... 

Before the 13th CGPM in 1967, when this definition was adopted, the unit was called the degree Kelvin (symbol °K, now K). 

Celsius temperature degree Celsius °c equal to kelvin and used in place of kelvin for expressing Celsius temperature, t, defined by equation t = T — where T is the thermodynamic temperature and Tq = 273.15 K by definition... 

The volume of a gas would theoretically be zero at a temperature of approximately -273°C or -460°F. Tliis temperature, wliich lias become known as absolute zero, is tlie basis for tlie definition of two absolute temperature scales, tlie Kelvin (K) and Rankine (°R) scales. The former is defined by shifting tlie Celsius scale by 273-Celsius degrees so that 0 K is equal to -273°C. Equation (4.2.3) shows tliis relation. 

The exact form of the function < > (T2, T being to some extent arbitrary, we might give several definitions of absolute temperature, all drawn up, however, in terms of the efficiency of the reversible engine. Lord Kelvin, in 1854, adopted the following form ... 

Temperature Scales A quantitative description of temperature requires the definition of a temperature scale. The two most commonly encountered in thermodynamics are the absolute or ideal gas (°A) scale and the thermodynamic or Kelvin (K) scale."... 

A triple point is a point where three phase boundaries meet on a phase diagram. For water, the triple point for the solid, liquid, and vapor phases lies at 4.6 Torr and 0.01°C (see Fig. 8.6). At this triple point, all three phases (ice, liquid, and vapor) coexist in mutual dynamic equilibrium solid is in equilibrium with liquid, liquid with vapor, and vapor with solid. The location of a triple point of a substance is a fixed property of that substance and cannot be changed by changing the conditions. The triple point of water is used to define the size of the kelvin by definition, there are exactly 273.16 kelvins between absolute zero and the triple point of water. Because the normal freezing point of water is found to lie 0.01 K below the triple point, 0°C corresponds to 273.15 K. 

Kelvin equivalent to 1 psia, 1 atm, 1 mm Hg, or some other pressure unit No definite answer can be given. Since this is always true, the method of steepest ascent can only tell whether a variable should be increased or decreased. It cannot tell how much one independent variable should be moved in relation to another one having different units. 

The second law of thermodynamics says that in a Carnot cycle Q/T = constant. This law allows for the definition of a temperature scale if we arbitrarily assign the value of a reference temperature. If we give the value T3 = 273.16K to the triple point (see Gibbs law, Section 8.2) of water, the temperature in kelvin units [K] can be expressed as ... 

Consultative Committee for Thermometry creation of a mise en pratique of die definition of the kelvin The Consultative Committee for Thermometry, considering that the ITS-90 and the PLTS-2000 are internationally accepted practical temperature scales defining temperatures T90 and T2qqq that are good approximations to thermodynamic temperature T... 

Taking up a 2005 recommendation of the Consultative Committee for Thermometry (CCT) [25], the Comite International des Poids et Mesures (CIPM) created a mise en practique of the definition of the kelvin containing clarifications and recommendations of the CCT concerning the realization of the definition of the kelvin and the implementation of practical temperature scales. 

Note 7 There are definitions of linear viscoelasticity which use integral equations instead of the differential equation in Definition 5.2. (See, for example, [11].) Such definitions have certain advantages regarding their mathematical generality. However, the approach in the present document, in terms of differential equations, has the advantage that the definitions and descriptions of various viscoelastic properties can be made in terms of commonly used mechano-mathematical models (e.g. the Maxwell and Voigt-Kelvin models). 

Note 4 Comparison with the general definition of linear viscoelastic behaviour shows that the polynomial /"(D) is of order zero, 0(D) is of order one, ago = a and a = p. Hence, a material described by the Voigt-Kelvin model is a solid (go > 0) without instantaneous elasticity (/"(D) is a polynomial of order one less than 0(D)). 

Note 6 For a Voigt-Kelvin solid (cf. note 3 and Definition 6.6, note 5), the equation describing the deformation becomes... 

Traditional thermodynamics gives a clear definition of entropy but unfortunately does not tell us what it is. An idea of the physical nature of entropy can be gained from statistical thermodynamics. Kelvin and Boltzmann recognised diat there was a relationship between entropy and probability (cf., disorder) of a system with the entropy given by... 

The ideal scale, as defined by (2.7a, b), also has an entirely different (and quite surprising ) theoretical basis, related to the maximum efficiency of machines and the second law of thermodynamics. This alternative definition of T(suggested by Kelvin) will be discussed in Section 4.5. However, we can recognize at this point that such a dual connection to fundamental thermodynamic principles of great universality gives (2.7a, b) a double-justification to be considered the true temperature scale. We henceforth adopt this definition of T throughout this book. 

According to Kelvin s definition, absolute Kelvin temperature TK can be consistently assigned in terms of the efficiency of the reversible engine operating between the two reservoir temperatures as... 

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