p8 - Albert Einstein 1879­1955 Albert Einstein 1879­1955...

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Unformatted text preview: Albert Einstein 1879­1955 Albert Einstein 1879­1955 • We believe in the possibility of a theory which is able to give a complete description of reality, the laws of which establish relations between the things themselves and not merely between their probabilities ... GOD DOES NOT PLAY DICE. Niels Bohr 1885­1962 Niels Bohr 1885­1962 • Einstein, DON'T TELL GOD WHAT TO DO! • Those who are not shocked when they first come across quantum mechanics cannot possibly have understood it. Werner Heisenberg 1901­1976 Werner Heisenberg 1901­1976 • We have to remember that what we observe is not nature itself but nature exposed to our method of questioning. • I, at any rate, am convinced that HE IS NOT PLAYING AT DICE. Erwin Schroedinger 1887­1961 Erwin Schroedinger 1887­1961 • I do not like it, and I am sorry I ever had anything to do with it. • Had I known that we were not going to get rid of this damned quantum jumping, I never would have involved myself in this business! Prince Louis de Broglie Prince Louis de Broglie 1892­1987 • Electrons should not be considered simply as particles, but that frequency must be assigned to them also. (1929, Nobel Prize Speech) Max Planck 1858­1947 Max Planck 1858­1947 • Physics is finished, young man. It's a dead­end street. (from an unknown teacher to Planck considering Physics at the turn of the 20th century!) THE ‘ULTRAVIOLET CATASTROPHE’ 1900 - Rayleigh This was a CLASSICAL prediction, first made in the late 19th century, that an IDEAL BLACK BODY at thermal equilibrium will emit radiation with INFINITE POWER. Max Planck resolved this issue by postulating that electromagnetic energy did not follow the classical description, but could only oscillate or be emitted in DISCRETE PACKETS OF ENERGY proportional to the frequency. He called these packets ‘QUANTA’. E = hυ Note: h = 6.626 x10 −34 J .s THE PHOTOELECTRIC EFFECT 1905 - Einstein The emission of electrons from a surface (usually metallic) upon exposure to, and absorption of, electromagnetic radiation. The photoelectric effect was explained mathematically by Einstein who extended the work on QUANTA as developed by Planck. KE = hυ − φ MILLIKAN’S OIL DROP EXPERIMENT 1909 - Robert Millikan This experiment determined the magnitude of the electronic charge, and that it was QUANTISED. This value is approximately 1.6 x10 −19 C Note: An electron volt (eV) is the amount of energy it takes to accelerate one electron through a potential of one volt. Thus, 1eV ≡ 1.6 x10 −19 J DE BROGLIE WAVELENGTH Prince Louis de Broglie - 1932 De Broglie discovered that all particles with momentum have an associated wavelength. λ= h h = p mv What is the wavelength of a human being, assuming he/she weighs 70 kg, and is running at 25 m/s? NUCLEAR ATOM STRUCTURES 1898 - Thomson 1911 -Rutherford 1913 - Rutherford/Bohr Atomic Line Spectra • General expression: • Lyman: • Balmer: • • Paschen: Brackett: 1 1 1 = R 2 − 2 λ 1 n hcR En = − 2 n n>1 (ultraviolet) n>2 (visible) n>3 (infrared) n>4 (infrared) n>5 (infrared) 1 1 1 = R 2 − 2 λ n 2 1 1 1 = R 2 − 2 λ n 3 1 1 1 = R 2 − 2 λ n 4 1 1 1 = R 2 − 2 λ n 5 • Pfund: SUMMARY OF IMPORTANT EQUATIONS SUMMARY OF IMPORTANT EQUATIONS • Energy and frequency: • The photoelectric effect: • De Broglie wavelength: • Angular frequency: hc E = hυ = λ KE = hυ − φ h h λ= = p mv ω = 2π f Equations of interest Equations of interest (non­examinable!) • Planck’s constant: • Wave vector: • h = 2π k= 2π λ ∂Ψ h2 2 =− ∇ Ψ +VΨ Schroedinger: ih ∂t 2m Richard Feynman 1918­1988 Richard Feynman 1918­1988 • Anyone who has not been shocked by quantum physics has not understood it. • The word 'quantum' refers to this peculiar aspect of nature that goes against common sense. Groucho Marx 1890­1977 Groucho Marx 1890­1977 • Very interesting theory ­ it makes no sense at all! QUANTUM THEORY QUANTUM THEORY Uses Explains • • • • • • • LASERs Semiconductors Transistors LED Night Vision Goggles CCD MRI / PET • Tunnelling • Radioactive decay • Periodic table (Pauli Exclusion Principle explanation to Mendeleev’s chart) THE FUTURE OF QUANTUM? THE FUTURE OF QUANTUM? • • • • • • Dot LASERs Logic gates Computing Cryptography / Encryption Cloning Teleportation ...
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