DOC PREVIEW
UK PHY 213 - Lecture Notes

This preview shows page 1-2-14-15-30-31 out of 31 pages.

Save
View full document
View full document
Premium Document
Do you want full access? Go Premium and unlock all 31 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 31 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 31 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 31 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 31 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 31 pages.
Access to all documents
Download any document
Ad free experience
Premium Document
Do you want full access? Go Premium and unlock all 31 pages.
Access to all documents
Download any document
Ad free experience

Unformatted text preview:

Key IdeasImportant ConceptsChapter 27 Quantum PhysicsSlide 4Slide 5Slide 6Planck’s quantum hypothesisThe energy is quantized!The Photoelectric EffectPhoton Theory of LightSlide 11Slide 12Photon Theory of Light makes the following predictions:Slide 14Slide 15Slide 16Compton EffectSlide 18Slide 19Wave-Particle DualityThe wave and particle aspects of matter complement one anotherSlide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Particles and WavesSlide 31Key Ideas Two Principles of Relativity:Two Principles of Relativity: •The laws of physics are the samesame for all uniformly moving observers. •The speed of light is the samesame for all observers. Consequences: Consequences: •Different observers measure differentdifferent times, lengths, and masses. •Only spacetimespacetime is observer-independent.Important ConceptsImportant ConceptsE=mc2t = T[1 - (v/c)2]1/2 l=L[1 - (v/c)2]1/2 m=mo/(1-v2/c2)1/2 KE=mc2-moc2=moc2/(1-v2/c2)1/2 – moc2Chapter 27Chapter 27 Quantum Physics Quantum PhysicsPhotoelectric EffectPhotoelectric EffectCompton EffectCompton EffectPhoton Theory of LightPhoton Theory of LightWave Nature of MatterWave Nature of MatterWave-Particle DualityWave-Particle DualityWave FunctionWave FunctionUncertainty PrincipleUncertainty PrincipleIdeas of quantum theory were developed when classical physics could not explain a handful of physical phenomena observed in beginning of the 20th centuryBlackbody RadiationBlackbody RadiationExperimental Results Wien’s LawpT=2.90x10-3 m • KPredictions of classical PhysicsPlanck’s quantum hypothesisPlanck’s quantum hypothesisPlanck's model required that the energy in the atomic vibrations of frequency f was some integer times a small, minimum, discrete energy, EEminmin = hf = hfwhere h is a constant, now known as Planck's constant, h = 6.626176 x 10-34 J•sPlanck's proposal then requires that all the energy in the atomic vibrations with frequency f can be written as E = n h fE = n h fwhere n in an integer, n = 1, 2, 3, . . . No other values of the energy were allowed.The energy is The energy is quantizedquantized!Planck did not realize how radical and far-reaching his proposals were. He viewed his strange assumptions as mathematical constructions to provide a formula that fit the experimental data.It was not until later, when Einstein used very similar ideas to explain the Photoelectric Effect in 1905, that it was realized that these assumptions described "real physics" and were much more than mathematical constructions to provide the right formula.The Photoelectric EffectThe Photoelectric EffectHeinrich Hertz first observed this photoelectric effect in 1887. This, too, was one of a few phenomena that Classical Physics could not explain. Light falling on a metal can cause electrons to be ejected from the metal. This is known as the photoelectric effect:Photon Theory of LightPhoton Theory of Light In 1905 Albert Einstein provided a daring extension of Planck's quantum hypothesis and proposed that the energy of the light is contained in "packets" or quanta each with energy of E = h f where again h is Planck's constant and f is the frequency of the light. All of the energy in one quantum -- now called a photon -- is given to one electron.For light with a frequency f greater than some particular threshold frequency, there would be enough energy and the electron would be ejected. From the conservation of energy, we would expect the electron to leave with kinetic energy KE given by h f = KE + W or KE = h f – W where W is the amount of work that must be done to separate an electron from the metal. For the least strongly bound electrons this amount of work is known as the "work function" and is labeled Wo. These electrons will leave with the greatest kinetic energy KEmax which is given by h f = KEh f = KEmaxmax + W + Woo or KE or KEmaxmax = h f - W = h f - WooWWoo is the minimum energy needed to remove an electron from a surface is the minimum energy needed to remove an electron from a surfacePhotoelectron energy increases with frequency of incident light (KEmax = h f – Wo)An increase in the intensity of the light only means an increase in the number of photons so more electrons will be ejected. But there will be no increase in the maximum energy of the electrons.Kinetic Energy can never be negative so this equation defines a threshold frequency, fo, from h fo = Wo If the frequency of the light is below this threshold frequency fo there will be no photoelectrons ejected from the metal.In 1913 and 1914 Robert A Millikan carried out careful experiments and measured precisely what Einstein's new theory predicted. Photon Theory of Light makes the Photon Theory of Light makes the following predictions:following predictions:Question: Photoelectrons are emitted by a metal surface only when the light directed at it exceeds a certain minimum(a) wavelength(b) frequency(c) speed(d) chargeAnswer: bQuestion: When light is directed on a metal surface, the energies of the emitted electrons(a) vary with the intensity of the light(b) vary with the frequency of the light(c) vary with the speed of the light (d) are random Answer: bCompton EffectCompton Effect Scattered electronTarget electronScattered photonhfhf’Change in photon energy=electron kinetic energyhf - hf’=KEPhoton momentum p=hf/c [i.e., mpc=(hf/c2)c]After a collision between a photon and electron1/f – 1/f’ = (h/m1/f – 1/f’ = (h/moocc22)(1-cos)(1-cos))The greater the scattering angle, the greater should be the The greater the scattering angle, the greater should be the change in frequencychange in frequencyNote: it still travels at c,but its f is lowerCompton effect verifies that photons do indeed possess the momentum p=hf/c and do indeed behave like particles in collisions: the quantum nature of light with the quantum nature of light with ordinary conservation of momentum and ordinary conservation of momentum and energyenergy However, Young's double slit experiment had shown conclusively that light was a wave, not a particle.Wave-Particle DualityWave-Particle DualityLouis de Broglie (1892-1987)de Broglie proposed that electrons, too, have a wave nature and a wavelength and that all material objects have a wave nature. In particular, de Broglie proposed that the wavelength of a body could be found from= h/p= h/mv This wave is


View Full Document

UK PHY 213 - Lecture Notes

Documents in this Course
SYLLABUS

SYLLABUS

10 pages

SYLLABUS

SYLLABUS

12 pages

SYLLABUS

SYLLABUS

10 pages

Load more
Download Lecture Notes
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 Lecture Notes 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 Lecture Notes 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?