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CU-Boulder PHYS 3070 - Lecture Notes

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Judah Levine, 3070L15 1http://physics.colorado.edu/phys3070http://physics.colorado.edu/phys3070Judah LevineJudah LevineJILA SJILA [email protected]@colorado.edu303 492303 492--7785 (27785 (2--7785)7785)M,F 11M,F 11--Noon, W 1Noon, W 1--3 pm3 pmalso by appointmentalso by appointmentJudah Levine, 3070L15 2Electrical circuit parametersElectrical circuit parametersohmsinrr wattsilosspowerwattssecondjoulesecondchargechargejouleviampsVoltssecondchargeiampscurrentchargejoulesvVolts2===×==×=====Energy transfer/work requires motion of chargesJudah Levine, 3070L15 3Transmission efficiencyTransmission efficiency%92130012001001101101201200120120022====×=======×=inputoutputefficiencywattslossohmrampsivoltsvwattsprilossontransmissiivdeliveredpowerJudah Levine, 3070L15 4Transmission efficiencyTransmission efficiency=====×=efficiencyohmrvoltsvwattsprilossontransmissiivdeliveredpower124012002A: 88%B: 92%C: 96%D: 98%E: 100%Judah Levine, 3070L15 5Transmission efficiencyTransmission efficiency%98122512002515152401200240120022====×=======×=inputoutputefficiencywattslossohmrampsivoltsvwattsprilossontransmissiivdeliveredpowerAnswer= DJudah Levine, 3070L15 633--phase Delta transmissionphase Delta transmissionJudah Levine, 3070L15 7High Voltage transmissionHigh Voltage transmissionJudah Levine, 3070L15 8StepStep--down transformerdown transformerStep up andStep downpossible only withalternating currentsystemsJudah Levine, 3070L15 9Alternating vs. Direct currentAlternating vs. Direct currentExtra credit report:“War of the currents”Thomas Edison vs. Nikola Tesla and George Westinghouse1 paragraph min, 1 page max by Wednesday, 8 March, 9 amJudah Levine, 3070L15 10What is light?Judah Levine, 3070L15 11Light as a waveLight as a waveWavelength= distance between wave crests1 micron=10-6m1 nano-meter=1nm=10-9m< 10 nm X-rays, gamma rays, …< 400 nm ultra-violet400 nm blue500 nm green670 nm red> 700 nm near infrared>1000 nm = 1micron= far infraredcm – km: microwaves, TV, FM, AM …Judah Levine, 3070L15 12Absorption and ReflectionAbsorption and ReflectionIncident energy= absorption + reflectionFocus on simple materials that have no wavelength dependenceWhite.Gray.BlackJudah Levine, 3070L15 13A Black BodyA Black BodyAbsorbs all radiation that falls on itKinetic energy of atoms radiateselectromagnetic energyWhat is spectrum of the radiation?Judah Levine, 3070L15 14Judah Levine, 3070L15 15WiendisplacementlawmTµλ2898max=Judah Levine, 3070L15 16Black body radiationBlack body radiation28424282445910811033001067.5mwAPTKKTKmwmwTAP=×=×==×==−σσmKTmTµλµλ103002898maxmax===Judah Levine, 3070L15 17AlmostAlmost--black bodyblack body11067.542824≤=×==−emissivityKmwmwTAPεσεσSame spectrum as black bodyJudah Levine, 3070L15 18Equilibrium of black bodyEquilibrium of black bodyRadiated energy= Incident energySuppose incident energy= 1000 W/m2FCKTTTTmw19791364108.11067.5100010001048442===×=×==−σJudah Levine, 3070L15 19Equilibrium of black bodyEquilibrium of black bodyRadiated energy= Incident energySuppose incident energy= 600 W/m2What is equilibrium temperature now?A: 273KB: 300KC: 321KD: 350KE: 364KJudah Levine, 3070L15 20Equilibrium of black bodyEquilibrium of black bodyRadiated energy= Incident energySuppose incident energy= 600 w/m2What is equilibrium temperature now?FCKTTTTmw118483211006.11067.56006001048442===×=×==−σAnswer= CJudah Levine, 3070L15 21Active Solar heatingActive Solar heating)(5005.0580028985800maxgreennmmKT====µλBlack-body absorberHot-water tubesmCKTµλ8.83302898)57(330max===Transparent to visibleOpaque to infra-redJudah Levine, 3070L15 22Passive Solar HeatingPassive Solar HeatingHeavyBlack bodyJudah Levine, 3070L15 23SolarSolar--driven heat enginesdriven heat engines“white body”reflectorBlack body absorberDiameter of mirror = 2marea= 3m2Suppose 600 w/m2Power=600×3=1800 wAbsorber= 10cm squareArea=


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CU-Boulder PHYS 3070 - Lecture Notes

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