1.1: Classical Physics of the 1890s. CHAPTER 1 The Birth of Modern Physics. Triumph of Classical Physics: The Conservation Laws.

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CHAPTER 1 The Birth of Moder Physics 1.1: Classical Physics of the 1890s 1.1 Classical Physics of the 1890s 1.2 The Kietic Theory of Gases 1.3 Waves ad Particles 1.

1 The more importat fudametal laws ad facts of physical sciece have all bee discovered, ad these are ow so firmly established that the possibility of their ever beig supplated i coseuece of ew

1 CHAPTER 1 The Birth of Moder Physics 1.1: Classical Physics of the 1890s 1.1 Classical Physics of the 1890s 1.2 The Kietic Theory of Gases 1.3 Waves ad Particles 1.4 Coservatio Laws ad Fudametal Forces 1.5 The Atomic Theory of Matter 1.6 Uresolved Questios of 1895 ad New Horizos Mechaics Electromagetism Thermodyamics MECHANICS CLASSICAL PHYSICS 1.1 The more importat fudametal laws ad facts of physical sciece have all bee discovered, ad these are ow so firmly established that the possibility of their ever beig supplated i coseuece of ew discoveries is exceedigly remote Our future discoveries must be looked for i the sixth place of decimals. - Albert A. Michelso, 1894 ELECTRICITY AND MAGNETISM THERMODYNAMICS CONSERVATION LAWS Triumph of Classical Physics: The Coservatio Laws Coservatio of eergy: The total sum of eergy (i all its forms) is coserved i all iteractios. Coservatio of liear mometum: I the absece of exteral forces, liear mometum is coserved i all iteractios. Coservatio of agular mometum: I the absece of exteral torue, agular mometum is coserved i all iteractios. Coservatio of charge: Electric charge is coserved i all iteractios. Mechaics Galileo ( ) Great experimetalist Priciple of iertia Established experimetal foudatios

2 Isaac Newto ( ) Three laws describig the relatioship betwee mass ad acceleratio. Newto s first law (law of iertia): A object i motio with a costat velocity will cotiue i motio uless acted upo by some et exteral force. Newto s secod law: Itroduces force (F) as resposible for the the chage i liear mometum (p): Newto s third law (law of actio ad reactio): The force exerted by body 1 o body 2 is eual i magitude ad opposite i directio to the force that body 2 exerts o body 1. Electromagetism Cotributios made by: Coulomb ( ) Oersted ( ) Youg ( ) Ampère ( ) Faraday ( ) Hery ( ) Maxwell ( ) Hertz ( ) Maxwell s Euatios Gauss s law (Φ E ): (electric field) Thermodyamics Cotributios made by: Gauss s law (Φ B ): (magetic field) Faraday s law: Ampère s law: (Geeralized) Loretz law: (force) _ F = _ E + _ v _ B Bejami Thompso ( ) (Cout Rumford) Sadi Carot ( ) James Joule ( ) Rudolf Clausius ( ) William Thompso ( ) (Lord Kelvi)

3 Primary Results The Laws of Thermodyamics Deals with temperature, heat, work, ad the iteral eergy of systems Itroduces thermal euilibrium Itroduces the cocept of iteral eergy Creates temperature as a measure of iteral eergy First law: The chage i the iteral eergy ΔU of a system is eual to the heat Q added to a system plus the work W doe by the system ΔU = Q + W Secod law: It is ot possible to covert heat completely ito work without some other chage takig place. The zeroth law: Two systems i thermal euilibrium with a third system are i thermal euilibrium with each other. Third law: It is ot possible to achieve a absolute zero temperature. 1.2: The Kietic Theory of Gases Cotributios made by: Robert Boyle ( ) Jacues Charles ( ) Joseph Louis Gay-Lussac ( ) Culmiates i the ideal gas euatio for moles of a simple gas: PV = RT (where R is the ideal gas costat, 8.31 J/mol K) Additioal Cotributios Amedeo Avogadro ( ) Joh Dalto ( ) Daiel Beroulli ( ) Ludwig Boltzma ( ) James Clerk Maxwell ( ) J. Willard Gibbs ( )

4 Primary Results Primary Results Average molecular kietic eergy directly related to absolute temperature Iteral eergy U directly related to the average molecular kietic eergy Iteral eergy eually distributed amog the umber of degrees of freedom (f ) of the system 1. The molar heat capacity (c V ) is give by (N A = Avogadro s Number) Other Primary Results 1.3: Waves ad Particles 2. Maxwell derives a relatio for the molecular speed distributio f (v): Two ways i which eergy is trasported: 1) Poit mass iteractio: trasfers of mometum ad kietic eergy: particles 3. Boltzma cotributes to determie the root-measuare of the molecular speed Thus relatig eergy to the temperature for a ideal gas 2) Exteded regios wherei eergy trasfers by way of vibratios ad rotatios are observed: waves

5 Is It a Wave or a Particles? Duality E&M-Waves behavig like Particles? Particles behavig like Waves? Is It a Wave or a Particles? Duality EM-Waves behavig like Particles? Particles behavig like Waves?! > D Wave! > D Wave! << D Particle! << D Particle Particles vs. Waves The Nature of Light Two distict pheomea describig physical iteractios Particles i the form of poit masses ad waves i the form of perturbatio i a mass distributio, i.e., a material medium The distictios are observatioally uite clear; however, ot so for the case of visible light Thus by the 17 th cetury begis the major disagreemet cocerig the ature of light Cotributios made by: Isaac Newto ( ) Christia Huyges ( ) Thomas Youg ( ) Augusti Fresel ( )

6 The Nature of Light The Nature of Light Newto promotes the corpuscular (particle) theory Particles of light travel i straight lies (?) or rays Explaied sharp shadows Explaied reflectio ad refractio Christia Huyges promotes the wave theory Light propagates as a wave of cocetric circles from the poit of origi Explaied reflectio ad refractio Did ot explai sharp shadows The Wave Theory Advaces The Electromagetic Spectrum Cotributios by Huyges, Youg, Fresel ad Maxwell Double-slit iterferece patters Refractio of light from a vacuum to a omedium Light was a electromagetic pheomeo Establishes that light propagates as a wave Visible light covers oly a small rage of the total electromagetic spectrum All electromagetic waves travel i a vacuum with a speed c give by: (where μ 0 ad ε 0 are the respective permeability ad permittivity of free space)

7 Double-slit Diffractio Experimet light

$INDIVIDUAL PHOTON HITS Although diffractio of light is a wave pheomeo, there is o$ $disitegrated i the Diffractio process to make a smooth diffractio patter Comig back$

8 INDIVIDUAL PHOTON HITS Although diffractio of light is a wave pheomeo, there is o smooth distributio of light i the diffractio patter, but the patter is rather formed of may idividual hits of particles the photos A sigle photo DOES NOT get disitegrated i the Diffractio process to make a smooth diffractio patter Comig back to that soo

9 Electromagetic waves (light) Waves? Particles (photos) Massive Particles 1.4: Coservatio Laws ad Fudametal Forces Recall the fudametal coservatio laws: Coservatio of eergy Coservatio of liear mometum Coservatio of agular mometum Coservatio of electric charge Later we will establish the coservatio of mass as part of the coservatio of eergy Moder Results Also i the Moder Cotext I additio to the classical coservatio laws, two moder results will iclude: The coservatio of baryos ad leptos The fudametal ivariace priciples for time reversal, distace, ad parity The three fudametal forces are itroduced Gravitatioal: Electroweak Weak: Resposible for uclear beta decay ad effective oly over distaces of ~10 15 m Electromagetic: (Coulomb force) Strog: Resposible for holdig the ucleus together ad effective less tha ~10 15 m

Uificatio Uificatio of Forces Neutros ad protos are composed of uarks, which have the color force actig betwee them GUTs are attempts to uify electroweak ad strog forces Strig theory is oe of these

10 Uificatio Uificatio of Forces Neutros ad protos are composed of uarks, which have the color force actig betwee them GUTs are attempts to uify electroweak ad strog forces Strig theory is oe of these They have yet to be verified experimetally Maxwell uified the electric ad magetic forces as fudametally the same force; ow referred to as the electromagetic force I the 1970 s Glashow, Weiberg, ad Salem proposed the euivalece of the electromagetic ad the weak forces (at high eergy); ow referred to as the electroweak iteractio Goal: Uificatio of All Forces ito a Sigle Force 1.5: The Atomic Theory of Matter Iitiated by Democritus ad Leucippus (~450 B.C.) (first to us the Greek atomos, meaig idivisible ) I additio to fudametal cotributios by Boyle, Charles, ad Gay-Lussac, Proust ( ) proposes the law of defiite proportios Dalto advaces the atomic theory of matter to explai the law of defiite proportios Avogadro proposes that all gases at the same temperature, pressure, ad volume cotai the same umber of molecules (atoms); viz atoms Caizzaro ( ) makes the distictio betwee atoms ad molecules advacig the ideas of Avogadro.

11 Further Advaces i Atomic Theory Maxwell derives the speed distributio of atoms i a gas Robert Brow ( ) observes microscopic radom motio of suspeded grais of polle i water Eistei i the 20 th cetury explais this radom motio usig atomic theory Oppositio to the Theory Erst Mach ( ) opposes the theory o the basis of logical positivism, i.e., atoms beig usee place ito uestio their reality Wilhelm Ostwald ( ) supports this premise but o experimetal results of radioactivity, discrete spectral lies, ad the formatio of molecular structures Overwhelmig Evidece for Existece of Atoms Max Plack ( ) advaces the cocept to explai blackbody radiatio by use of submicroscopic uata Boltzma reuires existece of atoms for his advaces i statistical mechaics Albert Eistei ( ) uses molecules to explai Browia motio ad determies the approximate value of their size ad mass Jea Perri ( ) experimetally verifies Eistei s predictios 1.6: Uresolved Questios of 1895 ad New Horizos The atomic theory cotroversy raises fudametal uestios It was ot uiversally accepted The costitutes (if ay) of atoms became a sigificat uestio The structure of matter remaied ukow with certaity

12 Further Complicatios Three fudametal problems: The uestio of the existece of a electromagetic medium The problem of observed differeces i the electric ad magetic field betwee statioary ad movig referece systems The failure of classical physics to explai blackbody radiatio Additioal Discoveries Cotribute to the Complicatios Discovery of x-rays Discovery of radioactivity Discovery of the electro Discovery of the Zeema effect The Begiigs of Moder Physics These ew discoveries ad the may resultig complicatios reuired a revisio of the fudametal physical assumptios that culmiated i the huge successes of the classical foudatios. To this ed, the itroductio of the moder theory of relativity ad uatum mechaics becomes the startig poit of this most fasciatig revisio.

PowerPoint lecture notes for Thornton/Rex s Modern Physics, 4e

PowerPoint lecture notes for Thornton/Rex s Modern Physics, 4e Prepared by: Anthony Pitucco, Ph.D. Pima Community College Dept of Physics, Chair Tucson, Arizona CHAPTER 1 The Birth of Modern Physics 1.1