Physics 262/266. George Mason University. Prof. Paul So

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1 Physics 262/266 Gerge Masn University Prf. Paul S

2 PHYS 262/266 Annuncements WELCOME TO A NEW SEMESTER! Curse Website Recitatins - Officially starts next week - 5 sectins: ALL n Tuesday (12:30a, 1:30p, 2:30p, 3:30p, & 4:30p) - Prfs Niklic, Satija, and Yigit Hmewrk/Mastering Physics - 1 st HW due next Friday (February 2nd) 11:59p - Curse ID: MPSO95033

3 Curse Inf First 5 weeks: Thermdynamics vl.1 (PHYS 262 & 266) Mid 5 weeks: Optics vl. 2 (PHYS 262) Last 5 weeks: Mdern Physics vl. 3 (PHYS 262) Relativity Quantum Mechanics

4 Chapter 17: Temperature & Heat Tpics fr Disscusin thermmeters and temperature scales abslute zer and the Kelvin scale meaning f thermal equilibrium thermal expansin meaning f heat calrimetry calculatins mechanisms f heat transfer

5 Descriptin f Physical Systems micrscpic prperties f atms/mlecules that make up the system nt directly assciated with sense perceptins macrscpic bulk prperties f the system directly assciated with sense perceptins

6 Descriptin f Physical Systems variables: micrscpic xvapke,,,,, PE,... Thery: Classical/Quantum Mechanics Newtn s Eqs, Maxwell s Eqs, Schrdinger s Eq (later) variables: macrscpic TPVUS,,,,,... Thery: Thermdynamics 0 th Law f Therm. 1 st Law f Therm. 2 nd Law f Therm. Statistical Mechanics (e.g. Kinetic Thery)

7 Temperature (T) Cmmn usage: a measure f ht & cld Physics definitin: average KE f mlecules (mre n this next chapter) Physical changes assciated with T: Mst materials expand when heated Pressure f gas (in a clsed cntainer) with T Electrical resistance changes with T Materials radiate at different at different T State f matter change with T Ice water steam

8 Measuring Temperature/Thermmeter A small amunt f liquid will typically increase in vlume as temperatures rise. Mercury was chsen early n because it s dense; a small vlume can recrd a large temperature range. The pressure f a fixed vlume f gas will rise if temperature rises.

9 Measuring Temperature/Thermmeter Anther cmmnly used measuring device relies n the differential expansin f a bimetal strip. D bimetal strip D infrared sensr

10 Temperature Scales Celsius ( C) & Fahrenheit ( F) are traditinally defined with tw readily reprducible reference states: (new) 5 TC TF TF TC 32 5 Freezing pint & Biling pint f water at 1 atm.

11 Temperature Scales Celsius ( C) & Fahrenheit ( F) are traditinally defined with tw readily reprducible reference states: (new) 5 TC TF TF TC 32 5 Freezing pint & Biling pint f water at 1 atm.

12 Abslute Zer and the Kelvin Scale (K) A Gas Thermmeter with sufficiently diluted gas (~Ideal Gas)

13 Abslute Zer and the Kelvin Scale (K) Imprtant Experimental Observatins: 1. P vs. T relatinship is linear fr all dilute gases. 2. All curves extraplate t a single zer pint with zer pressure. These imply There exists a unique abslute zer reference pint and ne can define an abslute temperature scale with it. At this abslute zer pint, Kelvin T Scale (K) TC C T K T C

14 Thermal Equilibrium Observatin: When tw bjects at different T are brught tgether, they will eventually reach the same temperature and the system reaches an equilibrium state when n further physical changes ccur in the system. e.g. warm sda cans in a cler filled with ice

15 Thermal Equilibrium Additinal cncepts Heat (mre n this later): the transfer f energy between bjects with different T. Thermal Cntact: tw bjects are in thermal cntact if heat can transfer between them (nt necessary in physical cntact). Thermal equilibrium: the situatin in which tw bjects in thermal cntact cease t exchange energy by the prcess f heat.

16 The 0 th Law f Thermdynamics N heat flw between A-C and B-C. N heat flw between A-B. Nte: this transitive prperty is nt true fr all physical prcess, e.g. tw pieces f irn with a magnet but the 0 th Law have been shwn t be true experimentally.

17 Thermal Expansin (linear) Objects such as these railrad tracks will thermal expand when T increases. The size f the change will depend n the material. L L T 0 L L L L (1 T ) 0 0 T T T 0 is the cefficient f linear expansin

18 Thermal Expansin (vlume) Mlecules can be visualized as spheres cnnected by springs. At a given temperature, these mlecules vibrate accrding t the spring ptential energy. Because f the asymmetry f this ptential energy, the mlecules average separatin tends t increase with T. One can apprx. this vlume expansin by: V V T 0 is the cefficient f vlume expansin

19 Cefficients f Expansin Ntes: 1. These relatins are apprximately linear in a given range f T nly. & ~ cnstant in T range f interest. 3. Mst substances have & but sme are nt, e.g. water. Typically, 3

20 Linear and Vlume Expansin Rates V WHL Each f the linear dimensins expands accrding t the Linear Thermal Expansin equatin given previusly. W W W T, H H H T, L L L T (assuming material t be istrpic same in all directins) V ( W W T)( H H T )( L L T) 0 V V 3 V W H L W H TL W TH L W H L T T (nly terms up t T)