28 Thermal Physics Concepts [Syllabus 6093]

Temperature1. X°C=(X+273)K2. Goodthermometer● Sensitivetosmall temperaturechanges● Abletomeasuretherequiredrangeof temperatures3. Thermometric properties vary uniformly and continuously withtemperature4. Typesof thermometersProperty Examples Volumeof fixedmassof liquid Mercury-in-glassthermometer Alcohol-in-glassthermometer Electrical Resistance ResistanceThermometer ElectromotiveForce Thermocouplethermometer5. Icepoint (lower fixedpoint), puremeltingwaterSteampoint (upper fixedpoint), pureboilingwaterWhen mercurylevel inthermometer stemremainssteady, makeamarkL0 andL100 respectivelyKineticModel of Matter(Shape, volume, densityandcompressibility)6. Statesof matterState Arrangement /Motion Property Solid Most closely packedinaregular pattern Highest Density Incompressible Strongest intermolecularforces = particlesvibrate about fixedpositions Fixedshapeandvolume Liquid Closely packed andrandomlyarranged Higher density Incompressible Strong intermolecularforces = particles moveabout freely within theliquid Fixed volume but takestheshapeof container

Gas Far apart from oneanother and randomlyarranged Lowest density Compressible Weakest intermolecularforces = particles moveabout randomly at highspeeds No fixed shape andvolume 7. All matter is made up of molecules which are always incontinuousrandommotion8. Brownian motion: random, haphazard and constant motion oftiny particles suspended in a gas or liquid due to unevenbombardment ondierent sidesbythemoleculesinaction9. Duetobrownianmotion, moleculeswill evenspreadout10.Gas pressure due to collision of gas molecules with the walls ofcontainer (forceisexertedwhenair moleculehitsthewall)11.PV/Tisaconstant● Pressure-Temperature(Volumeisconstant)By kinetic model of gases, a rise in the temperature of thegas causes an increase in the kinetic energy andhence thespeedof gasmolecules. Thegasmoleculeswill bombardthewalls more vigorously and more frequently. The averageforce acting on the wall. Thus, pressure increases since P=F/A.● Volume-Temperature(Pressureisconstant)Repeat P-T + However, in order for the pressure to remainconstant, thegaswill expandeventually.● Pressure-Volume(Temperatureisconstant)When the volume of container decreases, the number ofgas molecules per unit volumeincreases. Thegasmoleculeswill bombard the walls more frequently. The average forceacting on the wall increases. Thus, pressure increases sinceP=F/A. Transfer of Thermal Energy12.Net heat flow from hotter object to cooler object until thermalequilibriumisreached13.Molecular Vibration:When one end of an object is heated, the particles at this endgain kinetic energy and vibrate faster and further apart. Theycollide with their less energetic neighbouring particles. Some oftheir energy is transferred to their neighbouring particles, whichin turn gain kinetic energy. In this way, heat is passedalongthe

object byvibratingparticles.14.FreeElectronDiusion:In addition to that, free electron diusion takes place in metals.When heated, free electrons