Tp 12 temperature (shared)
- 1. A-level Physics Unit G484: The Newtonian World Temperature Thermal physics
- 2. Temperature LOs To do 1. Define ‘internal energy’. 2. Write an expression for the mean k.e ( Ek ) of an atom in an ideal gas. 3. Explain how Ek is related to the internal energy (U) of an ideal gas. 4. Draw a graph to show the variation of pressure with absolute temperature for an ideal gas. Thermal physics
- 3. Lesson focus • Temperature Learning objectives At the end of the lesson you will be able to: • explain that thermal energy is transferred from a region of higher temperature to one of lower temperature; • explain that regions of equal temperature are in thermal equilibrium; • describe how there is an absolute scale of temperature (the ‘thermodynamic scale’) that does not depend on the property of any particular substance; • state that absolute zero is the temperature at which a substance has minimum internal energy. Thermal physics
- 4. Learning outcomes All of you should be able to • explain the meaning of thermal equilibrium; • explain in simple terms how absolute temperatures are measured; • explain the meaning of absolute zero; • convert the temperatures from celsius to kelvin (or vice versa). Some of you may be able to • explain why a substance at absolute zero cannot be said to have zero energy. Thermal physics
- 5. Heat and temperature LOs Heat (symbol: Q) Heat is defined as thermal energy in transit (flowing) – usually – from a hot region to a cooler region. The study of heat energy travelling in this way led to the science of thermodynamics. Question Can you think of a situation in which thermal energy flows from a cool region a warm region? LO 1: explain that thermal energy is transferred from a region of Thermal physics higher temperature to one of lower temperature
- 6. Heat and temperature LOs Heat (symbol: Q) Heat is defined as thermal energy in transit (flowing) – usually – from a hot region to a cooler region. Temperature Temperature is a measure of how or cold a body is and is related to the mean, translational kinetic energy of its particles. Thermal physics
- 7. What happens next? LOs Thermal physics
- 8. The zeroth law of thermodynamics LOs When two objects are in thermal equilibrium (at the same temperature) with a third object, they are also in thermal equilibrium with each other. B is in A is in equilibrium equilibrium B with C with B A C A and C are also, therefore, in equilibrium. If they are brought into contact there will be no net heat transfer. A and C are in thermal equilibrium with B. A and C are also in thermal equilibrium. To do - textbooks Write a definition of thermal equilibrium. Thermal physics LO 2: explain that regions of equal temperature are in thermal equilibrium
- 9. How is temperature measured? LOs Temperature is usually measured by taking advantage the thermometric property of a substance, e.g • the expansion of a liquid (such as mercury or alcohol) • the resistance of a metal (e.g platinum) Unfortunately, it is found that different types of thermometer do not agree with each other. Thermal physics
- 10. The thermodynamic scale of temperature LOs To solve this problem, Lord Kelvin proposed an absolute scale of temperature (the thermodynamic scale) based, not on the behaviour of a particular substance, but on the theoretical performance of a heat engine. A more practical scale of temperature is based on the behaviour of an ideal gas. Thermal physics
- 11. Constant volume gas thermometer LOs Thermal physics
- 12. The absolute scale of temperature LOs The known temperature used is that of the ‘triple point of water’ (273.16 K) • Kelvin scale video LO 3: describe how there is an absolute scale of temperature that Thermal physics does not depend on the property of any particular substance
- 13. The absolute scale of temperature LOs This scale of temperature gives rise to the concept of absolute zero. pV0 0 = pVTP 273.16 Where pV = 0 because an ideal gas at this temperature exerts no pressure. At this temperature, substances have a minimum (but not zero) internal energy (‘zero point energy’). To do - research Why it is not possible for the particles of a gas to have zero energy? LO 4: state that absolute zero is the temperature at Thermal physics which a substance has minimum internal energy
- 14. Temperature LOs To do Decide whether each of these statements is true or false. For each, say whether it is always true (or false). Provide correct versions of false statements. 1. Water boils at 273 K. 2. The pressure of a fixed volume of gas decreases at its temperature falls. 3. Objects in thermal equilibrium have the same temperature. 4. One degree Celsius and one degree kelvin are equal in size. 5. When a substance is heated its particles increase in size. 6. Heat flows from a hotter region to a cooler region. 7. The thermometric property of a thermocouple is the change of electrical resistance with temperature. 8. Water boils at 100 °C. 9. The resistance of a NTC thermistor increases with increasing temperature. Thermal physics