Chapter 21: Thermal physics Chapter outline ■ ■ ■
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understand and explain the transfer of thermal energy and the concept of thermal equilibrium understand how certain physical properties can be used to measure temperature understand the absolute temperature scale and convert between temperatures measured in Kelvin and in degrees Celsius compare the advantages and disadvantages of thermistors and thermocouples use a simple kinetic model of matter to explain the different states of matter, temperature and energy changes understand that the internal energy of a system is determined by the state of the system recall and use the first law of thermodynamics define and use specific heat capacity and specific latent heat
KEY TERMS
internal energy: the sum of the random distribution of kinetic and potential energies of the atoms or molecules of a system specific heat capacity of a substance: the energy required per unit mass to raise the temperature by 1 K (or 1°C) 136
specific latent heat of a substance: the energy required per kilogram to change its state without any change in temperature Equations: first law of thermodynamics: increase in internal energy = energy supplied by heating + energy supplied by doing work; ΔU q + w specific heat capacity = specific latent heat =
energy supplied E ;c= mass × temperature chang n e mΔθ
energy supplied E ; L= mass m
converting between Celsius and Kelvin scales of temperature: T(K ) = θ( C ) + 273.15
Exercise 21.1 Kinetic model and internal energy In the kinetic model of matter, we picture matter as being made of many particles (atoms, ions or molecules). The model can be used to explain many phenomena, and this exercise develops an understanding of the model at its simplest.