Thermodynamics

Abstract

The concept of temperature is basic in thermodynamics. It originates from our sensations, warm and cold. The most salient physical property of temperature is its tendency to equalize. Two bodies in contact (thermal contact !) will eventually have the same temperature, independent of their physical properties and the special kind of contact. Just this property is used to bring a substance to a given temperature, namely, by surrounding it with a heat bath. Then, by definition, substance and heat bath have the same temperature. To measure the temperature one can employ any physical property which changes continuously and reproducibly with temperature, e.g., volume, pressure, electrical resistivity, and many others. The temperature scale is fixed by convention. We will only mention a few of the many scales that have actually been used: the mercury thermometer, the gas thermometer, and the scale of absolute temperature (Kelvin scale). The mercury thermometer uses as temperature-sensitive property the volume difference of glass and mercury. The capillary of the thermometer is divided into one hundred equal parts between two points corresponding to melting ice (0 °C) and boiling water (100 °C)*. In the gas thermometer one measures the pressure p of an amount of gas (for instance, helium or nitrogen) contained in a volume V.