2Photo by Blake TippensTEMPERATURE is a measure of the average kinetic energy per molecule. The infrared radiation coming from the air canal in the ear passes through the optical system of the thermometer and is converted to an electrical signal that gives a digital reading of body temperature.
3Objectives: After finishing this unit, you should be able to: Work with Celsius, Kelvin, and Fahrenheit temperature scales for both specific temperatures and temperature intervals.Write and apply formulas for linear, area, and volume expansion.
4Internal energy -- spring analogies are helpful: Thermal EnergyThermal energy is the total internal energy of an object: the sum of its molecular kinetic and potential energies.Thermal energy = U + KInternal energy -- spring analogies are helpful:U = ½kx2K = ½mv2
5TemperatureTemperature is related to the kinetic activity of the molecules, whereas expansion and phase changes of substances are more related to potential energy.Although not true in all cases, a good beginning is to define temperature as the average kinetic energy per molecule.
6Temperature vs. Internal Energy The large pitcher and the small one have the same temperature, but they do not have the same thermal energy. A larger quantity of hot water melts more of the ice.
7Temperature Equilibrium Heat is defined as the transfer of thermal energy that is due to a difference in temperature.Thermal EquilibriumHot CoalsInsulated ContainerTwo objects are in thermal equilibrium if and only if they have the same temperature.Cool WaterSame Temperature
8ThermometerA thermometer is any device which, through marked scales, can give an indication of its own temperature.T = kXX is thermometric property: Expansion, electric resistance, light wavelength, etc.
9Zeroth Law of Thermodynamics The Zeroth Law of Thermodynamics: If two objects A and B are separately in equilibrium with a third object C, then objects A and B are in thermal equilibrium with each other.AObject CABThermal EquilibriumSame TemperatureBObject C
10Temperature Scales1000C2120F00C320FThe lower fixed point is the ice point, the temperature at which ice and water coexist at 1 atm of pressure:00C or 320FThe upper fixed point is the steam point, the temperature at which steam and water coexist at 1 atm of pressure:1000C or F
11Comparison of Temperature Intervals 100 C0 = 180 F05 C0 = 9 F0tCtFIf the temperature changes from 790F to 700F, it means a decrease of 5 C0.
12Temperature Labels t = 600C If an object has a specific temperature, we place the degree symbol 0 before the scale (0C or 0F).t = 600CWe say: “The temperature is sixty degrees Celsius.”
13Temperature Labels (Cont.) If an object undergoes a change of temperature, we place the degree symbol 0 after the scale (C0 or F0) to indicate the interval of temperature.ti = 600Ctf = 200CDt = 600C – 200CDt = 40 C0We say: “The temperature decreases by forty Celsius degrees.”
14Specific Temperatures Same temperatures have different numbers: 0C 0F2120F320F1000C00C180 F0100 C0tCtF
15Convert 1600F to 0C from formula: Example 1: A plate of food cools from 1600F to 650F. What was the initial temperature in degrees Celsius? What is the change in temperature in Celsius degrees?Convert 1600F to 0C from formula:tC = 71.10C9 F0 = 5 C0Dt = 52.8 C0
16Limitations of Relative Scales The most serious problem with the Celsius and Fahrenheit scales is the existence of negative temperatures.-250C ?Clearly, the average kinetic energy per molecule is NOT zero at either 00C or 00F!T = kX = 0 ?
17Constant Volume Thermometer ValveConstant volume of a gas. (Air, for example)Absolute pressureA search for a true zero of temperature can be done with a constant-volume thermometer.For constant volume:T = kPThe pressure varies with temperature.
18Absolute Zero of Temperature 1000C00CP1P2T1T2Absolute ZeroPT-2730C00C1000CPlot points (P1, 00C) and (P2, 1000C); then extrapolate to zero.Absolute Zero = -2730C
20Linear Expansion to t Copper: = 1.7 x 10-5/C0 LoLtotCopper: = 1.7 x 10-5/C0Concrete: = 0.9 x 10-5/C0Iron: = 1.2 x 10-5/C0Aluminum: = 2.4 x 10-5/C0
21DL = aLoDt = (1.7 x 10-5/C0)(90 m)(80 C0) Example 2: A copper pipe is 90 m long at 200C. What is its new length when steam passes through the pipe at 1000C?Lo = 90 m, t0= 200CDt = 1000C - 200C = 80 C0DL = aLoDt = (1.7 x 10-5/C0)(90 m)(80 C0)DL = mL = Lo + DLL = 90 m mL = m
22Applications of Expansion Expansion JointsBimetallic StripBrassIronExpansion joints are necessary to allow concrete to expand, and bimetallic strips can be used for thermostats or to open and close circuits.
23Area Expansion Expansion on heating. A0 A Area expansion is analogous to the enlargement of a photograph.Example shows heated nut that shrinks to a tight fit after cooling down.
24Calculating Area Expansion A0 = L0W0 A = LWDWDLLLoWoWL = L0 + aL0 Dt W = W0 + aW0 DtL = L0(1 + aDt ) W = W0(1 + aDtA = LW = L0W0(1 + aDt)2A = A0(1 + 2a Dt)Area Expansion: DA = 2aA0 Dt
25Expansion is the same in all directions (L, W, and H), thus: Volume ExpansionExpansion is the same in all directions (L, W, and H), thus:DV = bV0 Dtb = 3aThe constant b is the coefficient of volume expansion.
26Vovr = bGV0 Dt - bPV0 Dt = (bG - bP )V0 Dt Example 3. A 200-cm3 Pyrex beaker is filled to the top with glycerine. The system is then heated from 200C to 800C. How much glycerine overflows the container?Vovr= ?V0V200C800C200 cm3Glycerine: b = 5.1 x 10-4/C0Pyrex: b = 3a b = 3(0.3 x 10-5/C0) b = 0.9 x 10-5/C0Vover = DVG - DVPVovr = bGV0 Dt - bPV0 Dt = (bG - bP )V0 DtVovr = (5.1 x 10-4/C x 10-5/C0)(200 cm3)(800C - 200C)
27Vovr = bGV0 Dt - bPV0 Dt = (bG - bP )V0 Dt Example 3. (CONTINUED)Vovr= ?V0V200C800C200 cm3Glycerine: b = 5.1 x 10-4/C0Pyrex: b = 3a b = 3(0.3 x 10-5/C0) b = 0.9 x 10-5/C0Vover = DVG - DVPVovr = bGV0 Dt - bPV0 Dt = (bG - bP )V0 DtVovr = (5.1 x 10-4/C x 10-5/C0)(200 cm3)(800C - 200C)Volume Overflow = 6.01 cm3
28SummaryThermal energy is the total internal energy of an object: the sum of its molecular kinetic and potential energies.Thermal energy = U + KThe Zeroth Law of Thermodynamics: If two objects A and B are separately in equilibrium with a third object C, then objects A and B are in thermal equilibrium with each other.ABThermal EquilibriumAObject CB
30Summary: Expansion Linear Expansion: to t Area Expansion: DA = 2aA0 Dt LoLtotDA = 2aA0 DtArea Expansion:ExpansionA0A
31Expansion is the same in all directions (L, W, and H), thus: Volume ExpansionExpansion is the same in all directions (L, W, and H), thus:DV = bV0 Dtb = 3aThe constant b is the coefficient of volume expansion.
32CONCLUSION: Chapter 16 Temperature and Expansion