Thermal Physics A lecture notes

Dunman High School (Senior High Physics Department) 9646 Physics Topic 6A: Thermal Physics (I) 6A-1 H2 Topic 6A Thermal Physics (I)

Dunman High School (Senior High Physics Department) 9646 Physics Topic 6A: Thermal Physics (I) 6A-2 Content  Temperature scales  Specific heat capacity  Specific latent heat Learning Outcomes Candidates should be able to (a) show an understanding that regions of equal temperature are in thermal equilibrium. (b) show an understanding that there is an absolute scale of temperature which does not depend on the property of any particular substance, i.e. the thermodynamic scale. (c) apply the concept that, on the thermodynamic (Kelvin) scale, absolute zero is the temperature at which all substances have a minimum internal energy. (d) convert temperatures measured in Kelvin to degrees Celsius: T / K = T / °C + 273.15. (e) define and use the concept of specific heat capacity, and identify the main principles of its determination by electrical methods. (f) define and use the concept of specific latent heat, and identify the main principles of its determination by electrical methods.

Dunman High School (Senior High Physics Department) 9646 Physics Topic 6A: Thermal Physics (I) 6A-3 6.0 Introduction In case you have not already realised, the concept of energy is central to the study of physics. As you have just learnt in the topic of Work, Energy & Power, energy can manifest in many different forms. The topic of The rmal Physics deals with several of these manifestations, which we term “heat”, “thermal energy” or, as you will learn later, “internal energy of a substance” . This study is important because energy in these forms is respo nsible for a host of phenomena which include how “hot ” an object is, s tate changes in substances, and chemical reactions. This topic is split into two different parts. This first set of notes deals with how we perceive heat at a macroscopic level. This involves temperature and a study of the thermal properties of matter. 6.1.1 Temperature & Thermometric Properties In general, w e measure the “hotness” of an object using a concept called “temperature”. In order to construct a suitable temperature “ruler” or scale, we may rely on the thermometric properties of substances. Intuitively, a thermometric property of a substance is a physical property that varies with hotness/temperature. Examples include:  Length (of a strip of metal)  Area (of a sheet of metal)  Volume (of a column of mercury)  Pressure (exerted by a gas on the surface of a container)

Dunman High School (Senior High Physics Department) 9646 Physics Topic 6A: Thermal Physics (I) 6A-4 A good thermometric property to set up a temperature scale would exhibit the following traits:  Measurable  Substance remains in the same state over the range of temperatures to be measured  Property varies linearly over the ran