Energy and the Environment Lecture 8 PHYS/ENVS 3070 Professor Dmitri Uzdensky Sept. 12, 2014 PHYS/ENVS 3070 1Announcements: • Finish Chapter 1, start reading Chapter 2. • CAPA Homework #2 due tonight, Sept. 12, 11pm. • Comments about this homework problems: • Problem 5 (water heater): typo in textbook’s inside cover correct value: 1 gallon = 3.785 liters. • Problem 7 (Boulder County population growth): this problem assumes exponential growth. • If you’re still puzzled by exponentials, read Appendix A.1 in the E&E book. If this doesn’t help, talk to a 3070 TA in the Help Room or come to my office hours. • Physics Help Room: sign in with your name and write the request time and course number (3070) on the chalk board. Sept. 12, 2014 PHYS/ENVS 3070 2My Great Idea (or Not) I have a Concept2 Rowing Machine at home. If I row for 20 minutes, it says I have burned “250 food Calories” (like the one jelly donut). That is about 106 Joules in 1200 seconds or a Power of 800 Watts. However, I am only about 10% efficient at producing useful work (the chain pulling a wheel), and thus I only could get out about 80 Watts of electricity generation (for example). So instead of paying $100 for my 1000 kWatt-hours of electricity last month, I could have just rowed for 12,000 hours ~ 500 days! Sept.&12,&2014& PHYS/ENVS&3070& 3&The&amount&of&energy&we&consume&far&exceeds&what&our&muscles&can&produce!&Today’s(Lecture:(• …&Other&forms&of&energy:&&– E&=&mc2&– Nuclear&Energy&– ElectromagneKc&RadiaKon&Energy&• Energy&ConsumpKon&in&the&United&States.&• Fossil&Fuels&Sept.&12,&2014& PHYS/ENVS&3070& 4&Another(Energy(!(Mass(Energy(2mcE =In&1905,&over&100&years&ago,&Albert&Einstein&discovered&that&mass&is&just&another&form&of&energy.&&m&is&mass&in&kilograms&(SI&Units);&c&=&3&x&108&m/s&=&300,000&km/sec&&]]]&speed&of&light&&&Sept.&12,&2014& PHYS/ENVS&3070& 5&KE =12mv2Compare&this&with&KineKc&Energy:&&&Here&is&Albert&Einstein&He&is&a&very&energeKc&person…&&How&much&energy&does&he&have?&&&Mass&=&65&kg&&2mcE == 65kg( )× (3×108m / s)2E = 6 ×1018 Joules !Consider&that&the&enKre&USA&uses&100&QBtu&or&1020&Joules&each&year.&&&Thus&the&energy&in&his&body&could&“run&all&the&lights”&for&17&out&of&365&days&in&a&year.&&&What&is&the&problem&with&this&idea?&Sept.&12,&2014& PHYS/ENVS&3070& 6&Chemical(Reac;ons&involve&atomic&electrons.&Typical&energy&per&reacKon&&&~&10]18&Joules&(or&10&eV)&Nuclear(Reac;ons&involve&protons&&&neutrons&inside&nucleus.&Typical&energy&per&reacKon&&~&10]11&Joules&(or&200&MeV)&Sept.&12,&2014& PHYS/ENVS&3070& 7&nucleus(electrons(proton(neutron(Chemical(and(Nuclear(reac;ons(However,&in&nuclear&reacKons,&we&someKmes&observe&that&there&was&a&lihle&more&mass&before&compared&with&aierwards.&Fission(Reac;on((SpliAng)(Fusion(Reac;on((Adding)(Sept.&12,&2014& PHYS/ENVS&3070& 8&Nuclear(Energy(U235&+&n&à&Ba141&+&Kr92&+&3n&U235&+&n&à&Te139&+&Zr94&+&3n&Fission(Energy(Release(If&you&add&the&masses&before&and&aier,&you&find&that&you&lost&about&&&&&&&&&&&&&3.6&x&10]28&kilograms&in&the&process!&Recalling&that&E=mc2&(where&c&=&3&x&108&m/s),&what&is&the&raKo&of&energy&from&1&kg&of&U]235&compared&to&that&from&a&1&kg&lump&of&coal&(2.4x107&J)?&(energy&content&per&unit&mass&is&called&specific(energy)&Avogadro&number&NA=&6x1023&atoms&of&Uranium&weigh&235&grams.&&Thus,&there&are&NU&=&NA&x&(1000/253)&=&2.5&x&1024&atoms&of&Uranium&in&1&kg.&&&Uranium&specific&energy&is&3&million&Kmes&the&coal&specific&energy!&E(Uranium) = Δm c2= (2.5 ×1024× (3.6 ×10−28kg))(3×108m / s)2~ 8 ×1013JSept.&12,&2014& PHYS/ENVS&3070& 9&Nuclear&fission&chain&reacKons&are&the¤t&power&source&for&nuclear&reactors.&&Uranium&is&the&fuel.&Nuclear&weapons&now&uKlize&both&fission(and(fusion&reacKons.&The&Sun&is&powered&by&fusion&reacKons&in&the&core.&&The&Sun&is&5&billion&years&old&and&will&conKnue&to&“burn” for&about&5&billion&more&years&before&it&runs&out&of&fuel.&Sept.&12,&2014& PHYS/ENVS&3070& 10&Electromagnetic Radiation Energy What is transmitting the energy to make you get a sunburn? Light is an electromagnetic wave (like radio waves, X-rays, and also visible light!). These waves carry energy. Sunlight is electromagnetic radiation emitted by the Sun that travels through empty space to us on Earth. It is the source of most of the energy available on Earth (even via the creation of fossil fuels a long time ago), except nuclear. Sept.&12,&2014& PHYS/ENVS&3070& 11&Sun&on&the&beach:&Sunburn&Note&that&“energy&conservaKon”&in&everyday&use&means&“using&less&energy”&like&turning&off&the&lights.&&&Not&the&same&as&our&physics&meaning&in&which&energy&is&conserved&for&every&process&in&the&universe.&Sept.&12,&2014& PHYS/ENVS&3070& 12&ENERGY(CONSERVATION(Energy&is&such&a&useful&concept&because&it&is&“Conserved”.&Energy(is(conserved.(According&to&laws&of&modern&physics,&the&exact&amount&of&energy&the&enKre&universe&started&out&with&14&billion&years&ago,&is&exactly&the&same&amount&of&energy&the&universe&has&today.&Sept.&12,&2014& PHYS/ENVS&3070& 13&We&always&talk&about&using&energy,&so&how&can&energy&be&conserved?&&It&turns&out&we&are&always&just&changing&one&form&of&energy&into&another.&&&&SomeKmes&the&new&form&of&energy&is&less&useful.&&&Many&different&forms&of&energy&–&but&they&are&all&energy&nonetheless.&&&&Sept.&12,&2014& PHYS/ENVS&3070& 14&Renewable(vs.(Nonrenewable(Energy(Sources(Renewable:&solar,&geothermal,&Kdal&Note:&Solar&includes&wind,&hydroelectric&power,&&ocean¤ts,&biomass…&NonOrenewable:&everything&else&Fossil&fuels&(coal,&oil,&gas,&etc.),&uranium&ore&etc.&Sept.&12,&2014& PHYS/ENVS&3070& 15&Energy(Usage(in(the(US(by(sec tor (Sept.&12,&2014& PHYS/ENVS&3070& 16&Total&US&energy&usage:&100&QBtu/yr&&=&100&x&1015&Btu/yr&&&=&1017&Btu/yr&=&1020&J.&&Average&usage&per&person:&3&x&108&Btu/year&=&&3&x&1011&J/year&&=&300&GJ/&year.&Sept.&12,&2014& PHYS/ENVS&3070& 17&Sept.&12,&2014& PHYS/ENVS&3070& 18&>80%&of&energy&supplied&via&fossil&fuels!&What&is&the&total&percentage&of&US&energy&consumpKon&that&comes&from&fossil&fuels?&&A)&<20% & &B)&30%&C)& &50% & &D)&>80%&Clicker(Ques;on(Room&Frequency&DC&FOSSIL(FUELS(85% of US energy supply comes from fossil fuels ! Sept.&12,&2014& PHYS/ENVS&3070&
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