Thermal Physics / Heat and Thermodynamics PDF

THERMAL PHYSICS / HEAT AND THERMODYNAMICS PHY 101: ENGINERING PHYSICS Thermodynamic concepts 2 3  Internal Energy: It is defined as the sum of kinetic energy and potential energy of a substance and is the result of the motion of the particles which make up th...

THERMAL PHYSICS / HEAT AND THERMODYNAMICS PHY 101: ENGINERING PHYSICS Thermodynamic concepts 2 3  Internal Energy: It is defined as the sum of kinetic energy and potential energy of a substance and is the result of the motion of the particles which make up the substance. Heat: It is defined as the transfer of energy from one object to another and is usually the result of the objects with different temperatures. An ideal gas is a theoretical gas composed of many randomly moving point particles that are not subject to interparticle interactions. 4  It is the study of thermal energy/heat energy. The central concept of thermodynamics is temperature. Temperature is the degree of hotness or coldness of a body expressed on some scale. Temperature is measured in Kelvin (K). Temperature is measured by a thermometer. Types of Thermometers. 1) Constant – volume gas thermometers. 2) Resistance thermometers. 3) Mercury – in – glass thermometers. 4) Electric thermometers. 5) Thermocouple thermometers. 5  Zeroth Law When a body, ‘A’, is in thermal equilibrium with another body, ‘b’, and also separately in thermal equilibrium with a body ‘, C’, then body, ‘B’ and ‘C’, will also be in thermal equilibrium with each other. This statement defines the zeroth law of thermodynamics. The law is based on temperature measurement. 6 First law of thermodynamics 𝑑𝑄 = 𝑑𝑈 + 𝑑𝑊 7  Internal energy Thermodynamic Processes 8 9 Work done in various processes 10 11 12 13 Exercise: An ideal gas expands from the state (P1,V1) to the state (P2,V2) where P2=2P1 and V2=2V1. The expansion proceeds along the path ACB in the Figure below. Find an expression for the work done by the gas during this process. The equipartition theorem The equipartition theorem states that energy is shared equally amongst all energetically accessible degrees of freedom of a system. 14  Kinetic theory of gases Kinetic theory is used to explain the behaviour of gases in terms of motion of their molecules. The theory postulates that a gas consists of numerous molecules moving at high velocities in random motion, as well as with the walls of the container. This theory is based on the following assumptions: 1) The volume of the molecules is negligible compared to the volume occupied by the gas (they may be considered as points). 2) There are no inter-molecular forces except during collisions. 3) All collisions are perfectly elastic, i.e. both kinetic energy and momentum are conserved. 4) Duration of collision is negligible compared to the time in between them. 15