Celsius temperature definition

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. 

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... 

Each of these properties can provide the basis for an operational definition of a temperarnre scale. For example, the Celsius temperature is defined by Equation (3.1) ... 

Name, Symbol kelvin, K-(temperature) Definition The kelvin is the fraction 1/273.16 of the thermodynamic temperature of the triple point of water. The kelvin is a unit of thermodynamic temperature (T). The word (or symbol) degree is not used with kelvin. The Celsius (formerly centigrade) temperature is also used. Celsius temperature (symbol f) is defined by the equation t = T — T0, where T0 equals 273.15 K. A degree Celsius (°C) is thus equal to one kelvin. 

The definitions of standard states given in Section II.3 make no reference to fixed temperature. Hence, it is theoretically possible to have an infinite number of standard states of a substance as the temperature varies. It is, however, convenient to complete the definition of the standard state in a particular context by choosing a reference temperature. As recommended by lUPAC [82LAF], the reference temperature chosen in the NEA-TDB project sT= 298.15 K or = 25.00°C. Where necessary for the discussion, values of experimentally measured temperatures are reported after conversion to the IPTS-68 [69COM]. The relation between the absolute temperature T(K, kelvin) and the Celsius temperature t (°C) is defined by t = T- Tf) where Tj, = 273.15 K. 

E1.12(b) This exercise issimilartoExerci.se l. 12(a) in that it uses the definition ofabsolutezeroas that temperature at which the volume of a sample of gas would become zero if the substance remained a gas at low temperatures. The solution uses the experimental fact that the volume is a linear function of the Celsius temperature. 

At the outset, it must be emphasised that the definition of low temperature is arbitrary. A life scientist would normally equate low temperature with subzero Celsius temperature , whereas to a physicist, perhaps studying superconductivity phenomenon, the term signifies temperatures in the neighbourhood of 1 Kelvin. The reason why low temperature is often equated with freezing is probably because the freezing point of ordinary water lies near the centre (measured in degree Celsius) of the temperature range —40 to - -40°C, which we associate with life processes on this planet. 

The unit of Celsius temperature is the degree Celsius, symbol °C. It is by definition equal in magnitude to the kelvin. The numerical value of a Celsius temperature t expressed in degrees Celsius is given by... 

Because of the way temperature scales used to be defined, it remains common practice to express a thermodynamic temperature, symbol T, in terms of its difference from the reference temperature 7b = 273.15 K, the ice point. This temperature difference is called the Celsius temperature, symbol t, and is defined by the equation t=T —To. The unit of Celsius temperature is the degree Celsius, symbol °C, which is, by definition, equal in magnitude to the kelvin. A difference or interval of tenperature may therefore be expressed either in kelvin or in degrees Celsius. 

This definition ensures that temperature intervals in the kelvin scale are identical with the temperature intervals in the Celsius scale. Thus, conversion from thermodynamic temperature T to Celsius temperature 6 is ... 

Thermometer readings shall be corrected to 101.3 kPa (760 mm Hg) pressure except when product definitions, qiecifications, or agreements between the purchaser and the seller indicate, specifically, that such correction is not required or that correction shall be made to some other base pressure. This report shall include the observed pressure and shall state whether corrections have or have not been applied. When the report is based on thermometer readings corrected to 101.3 kPa (760 mm Hg), obtain the correction to be applied to each thermometer reading by means of the Sydney Young equation as given in Eqs. 3,4, or 5, or by the use of Table 5. For Celsius temperatures ... 

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 general temperature scale now in use is the Celsius scale, based nominally on the melting point of ice at 0°C and the hoiling point of water at atmospheric pressure at 100°C. (By strict definition, the triple point of ice is 0.01°C at a pressure of 6.1 mhar.) On the Celsius scale, absolute zero is -2 73.15°C. 

Like pressure and volume, temperature is a thing of everyday experience and most people think they understand it, at least to the extent of being able to say that it is a measure of how hot or cold a body is relative to our senses. Giving a precise definition is more difficult, however. Also, the scales most commonly used to measure this quantity, Celsius and (less frequently these days) Fahrenheit, are arbitrary. The thermodynamic definition, ensconced in the zeroth law, essentially states that if there is no heat flow between two bodies, they are at the same temperature. This is not very enlightening and we will have to wait until we discuss what the molecules are doing to get more insight. Nevertheless, the idea that tempera-... 

Gas thermometers. The use of gases for thermometers is simplified by the fact, that the expansion of all gases obeys very nearly the same law as the expansion of mercury. When their temperature is raised one degree, all gases expand by a constant amount which is independent of the temperature and of the nature of the gas. (Cf. Chap. II.) In the case of mercury, this uniformity of expansion is a necessary consequence of the definition of the Celsius scale of temperature, since the total expansion between 0° and 100° was divided into 100 equal parts. 

The simphcity of the relationship between the thermodynamic scale and the gas thermometer scale is due principally to the simple properties of rarefied gases, and also to the fortunate choice of mercury as thermometric substance by Celsius and Reaumur before the discovery of the gas laws. The coefficient of expansion of mercury happens to be almost exactly proportional to the coefficient of expansion of rarefied gases. All our thermodynamical relationships would have been very much more comphcated had water or alcohol, for example, or the resistance of a metal, been used for the definition of the practical scale of temperature. Their strict validity, however, would not have been affected. 

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