Unformatted text preview:

p250c16:116: TemperatureTemperature:A quantitative measure of “hot” or “cold”Operational definition: Temperature is what is measured by a thermometer.mercury thermometerconstant volume gas thermometerbimetallic stripAll involve measurable physical changes in response to temperature changes.Temperature Scaleswater freezes water boilsFahrenheit 32º 212ºCelsius 0º 100º TF = 9/5 TC + 32p250c16:2Example: What is the temperature in celsius of “room temperature”? What would be a hot sunny day?p250c16:3Thermal Equilibrium: Two systems are placed in “thermal contact” until no further changes occur.Let A and B come into thermal contact with C, but not with each other. -A is in thermal equilibrium with C. -B is in thermal equilibrium with C.(simultaneously)Now, let A and B come into thermal contact with each other. -No further changes occur. => A and B are in thermal EquilibriumThe Zeroeth Law of Thermodynamics: Two systems in thermal equilibrium with a third system are in thermal equilibrium with each other. One parameter (temperature) determines equilibrium.System A System BSystem A System BSystem CSystem A System BSystem Cp250c16:4Gas thermometer and absolute temperature scalesConstant volume gas thermometerpressure changes indicate temperature changesAt low densities∆p ∝∆TAll gases have same x-interceptp = 0 at TC = −273ºC TF = −460ºFpT (Celsius)TC = 0ºCTC = −273ºCAbsolute temperature scales:T = 0 when p = 0Kelvin TK = TC + 273Rankine TR = TF + 460p250c16:5Thermal ExpansionA change in temperature causes a change in length in a solid object. Usually, change in length ∆Lis proportional to change in temperature, ∆Tis proportional to original length, L0depends upon type of materialL0∆LTLL ∆=∆0αα = Coefficient of Linear Expansion (sometime a)Determine α experimentally:TLL∆∆=10α))(1(0000TTLLLLL −+=∆+= αp250c16:6Example: The Eiffel tower is 301 m on a hot day (22°C) . By how much does it shrink when the temperature cools to a temperature of 0°C?p250c16:7Volume expansion (of solids and liquids)linear expansion in 3-D!A change in temperature causes a change in volume. The change in volume ∆Vis proportional to change in temperature, ∆Tis proportional to original length, V0depends upon type of materialTVV ∆=∆0ββ = Coefficient of volume expansion for solids, β= 3αHow are voids (holes) in materials affected by changing temperatures?p250c16:8Voids in materials expand and contract as if they were made of the material.Example: A copper flask with a volume of 150 cm3 is filled to the brim with olive oil. If the temperature of the system is increased from 6.0°C to 31°C, how much oil overflows?(copper α = 24E-6 K-1, olive oil: β = 0.68E-3 K-1 ) ...And then there's water...p250c16:9What is heat?One thing which is transferred between two systems initially at different temperatures as they come to thermal equilibrium.Heat is energy which is transferred solely because of temperature differences.Heat addition to a system can cause temperature changes.“Mechanical Equivalent” of Heat: 1 calorie = 4.187 joulesHeat Units, defined in terms of the properties of watercalorie: the energy required to raise the temperature of 1 gram of water by 1 ºC (4.187 J)kilocalorie: a.k.a. Calorie a.k.a. dietetic calorie = 1000 calories (4187 J)British Thermal Unit: the energy required to raise the temperature of 1 pound of water by 1 ºF (1060 J)Example: How many 20 cm steps must a 74.0 kg individual climb to work off a 305 Cal. milkshake?p250c16:10Specific HeatsFor a sample of a substance that does not undergo a change of state:Heat added: Q is proportional to∆T = Tf− Ti , the change in temperaturem, the mass of the sampleQ =C∆T= mc ∆T C is the heat capacity of a particular samplec is the material’s specific heat , so C= mcCalorimetry: Hot + Cool = WarmIn a closed system (hot object interacts with cool object)heat gained by cool object(+) + heat lost by hot object(−) =0Substance kJ/(kg ºC) kcal/(kg ºC) cal/(g ºC) Water 4.19 1.00 Glass .39 .093 Ice 2.09 0.50 Copper 0.39 0.093 Air 0.70 0.17 QCQH=0mCcCT −TCmHcHT −TH=0T =mCcCTCmHcHTHmCcCmHcHp250c16:11Example: what is the final temperature if 550 g of water at 32°C are poured into a 210 g aluminum container with an initial temperature of 15°C?Example 16-5/demo/lab: determine the specific heat of a sample by heating it, dropping in water and observing the changes of temperatures?p250c16:12Mechanisms of Heat TransferConductionConvection (Natural vs Forced)Radiation (Electromagnetic Waves)Conduction:No bulk motion of matterMicroscopic transfer of kinetic energy to adjacent regionsBecause KE of electrons in a conductor “easily” transported from one region to another, good electrical conductors are generally good thermal conductorsRate of heat flow:value"-R"Gradient eTemperaturty Conductivi Thermal1212 KLRLTTKLTTKAtQ==−=−=∆∆T2T1HAp250c16:13ConvectionBulk motion of fluid (forced or natural)chief mechanism of heat lost under most situationsCOMPLEX!!!Depends upon fluid and geometryh = skin coefficient; depends upon temperatures, fluid, geometry, etc.)(CHTThAtQH −==Radiation (electromagnetic waves)= “Blackbody” RadiationStephan- Boltsmann Law:)(/ )10( emissivity=ConstantBoltzmann -Stephan105.6705=/44428-4snetTTAeTQPeeKmWATeTQP−=∆∆=≤=⋅×=∆∆=σσσ<p250c16:14Example: One window in a house is 1.00 m on a side. The glass is 0.50 cm thick. How much heat is lost through this window each day if the indoor temperature is 21°C and the outside temperature is 0.0°C?p250c16:15Example: What is the net power lost by a (nearly) nude swimmer if he has a body temperature of 30°C and steps outside where the temperature is 0°C? Take his surface area to be 1.15 m2 and human skin emissivity to be


View Full Document

PSU PHYS 250 - Temperature

Download Temperature
Our administrator received your request to download this document. We will send you the file to your email shortly.
Loading Unlocking...
Login

Join to view Temperature and access 3M+ class-specific study document.

or
We will never post anything without your permission.
Don't have an account?
Sign Up

Join to view Temperature 2 2 and access 3M+ class-specific study document.

or

By creating an account you agree to our Privacy Policy and Terms Of Use

Already a member?