EJC Physics H208 Temperature and Ideal Gas 2023 - 1. Notes (full)

Page 1 of 16 9749(202 3) H2 Physics H208 Temperature and Ideal Gases – Notes H2 Topic 8 – Temperature and Ideal Gases Infrared Fever Screening Systems are a common sight in 2020 as the world battles the COVID- 19 pandemic. It was a world-first, made-in-Singapore system back in 2003 to respond to the need for fast, mass measurements of body temperatures when battling the SARS epidemic. The prototype was produced within a week of the Ministry of Health approaching the Defence Science and Technology Agency (DSTA) for assistance. Content • Thermal equilibrium • Temperature scales • Equation of state • Kinetic theory of gases • Kinetic energy of a molecule Learning Outcomes Candidates should be able to: (a) show an understanding that regions of equal temperature are in thermal equilibrium (b) explain how empirical evidence leads to the gas laws and to the idea of an absolute scale of temperature (i.e. the thermodynamic scale that is independent of the property of any particular substance and has an absolute zero) (c) convert temperatures measured in degrees Celsius to kelvin: T / K = T / °C + 273.15 (d) recall and use the equation of state for an ideal gas expressed as pV = nRT, where n is the amount of gas in moles (e) state that one mole of any substance contains 6.02 × 10 23 particles and use the Avogadro number N A = 6.02 × 1023 mol–1 (f) state the basic assumptions of the kinetic theory of gases (g) explain how molecular movement causes the pressure exerted by a gas and hence derive the relationship pV = ⅓ Nm<c2>, where N is the number of gas molecules (a simple model considering one-dimensi onal collisions and then extending to three dimensions using ⅓ <c2> = <cx2> is sufficient) (h) recall and apply the relationship that the mean kinetic energy of a molecule of an ideal gas is proportional to the thermodynamic temperature (i.e. ½ m<c2> = 3 2 kT) to new situations or to solve related problems.

Page 2 of 16 9749(202 3) H2 Physics H208 Temperature and Ideal Gases – Notes 8.0 Introduction Temperature, pressure, and volume are quantities that describe macroscopic properties of a system. Typically, when we discuss them, we refer to a bulk body of gas , liquid or solid. Together, the quantities ( T, p and V) define a state of a system; in the field of thermal physics we refer to gas/liquid/solid as phases. In this field of study of these macroscopic properties, physicists hypothesize simple m icroscopic models to explain the bulk behaviour - that the system consists a large number of objects having complex and random interactions. We often describe the collective behaviour of a large distribution of interacting objects by their statistical averages, which may be more meaningful than the chaos exhibited by individual objects. For example, rather than the individual changes in momentum of gas particles against the inner walls of the container, we describe the statistical average via t