Phys2212_24.1+to+24.5

Phys2212_24.1+to+24.5 - Physics 2212 Waves Lecture 5 Waves...

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Physics 2212 Waves Lecture 5 Waves and Matter
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10/06/09 Physics 2212 - Lecture 5 Spectroscopy Hot self-luminous objects light the Sun or a light bulb emit a continuous spectrum of wavelengths. In contract, light emitted in low=pressure gas discharge contains only discrete individual wavelengths, a discrete spectrum . These spectral lines can be recorded and measured using a grating spectroscope .
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10/06/09 Physics 2212 - Lecture 5 The Hydrogen Spectrum red blue violet Johann Jakob Balmer (1825 – 1898) The spectrum of hydrogen, as viewed in the visible region, shows the Balmer series of spectral lines. Balmer did not discover them, but he did notice a regularity in their spacing, and he found by trial and error that they could be represented by the relation: 1 2 2 1 1 (91.18 nm) 3,4,5,6 2 n n λ - = - =
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10/06/09 Physics 2212 - Lecture 5 The Balmer Series The Balmer series is now understood to be one of several series in hydrogen. They are produced by electron jumps from orbit n to orbit m , with m = 2 for the Balmer series. 1 2 2 1 1 (91.18 nm) m n λ - = -
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10/06/09 Physics 2212 - Lecture 5 The Discovery of X-Rays Wilhelm Conrad Roentgen (1845 - 1923) In 1895, Roentgen accidentally discovered that when electrons are pulled from a cathode (= negative terminal emitting electrons) with a high voltage and strike a heavy-metal anode (= positive terminal), an envelope of film with a key on top was exposed, except where it was covered by the key. He deduced that some invisible rays (which he called X-rays) were produced by the electrons and were exposing the film.
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10/06/09 Physics 2212 - Lecture 5 X-Ray Diffraction Max von Laue (1879 - 1960) In 1912, Max von Laue pointed out if that X-rays were a form of light, then it must be light with very short wavelengths, and that a crystal, which might have an inter-atom spacing on the order of 0.1 m, might act as a 3- dimensional diffraction grating for X- rays. This prediction was soon confirmed experimentally. Measurements showed that X-rays were indeed electromagnetic waves, and that they had wavelengths in the range 0.01 to 10.0 nm.
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10/06/09 Physics 2212 - Lecture 5 Bragg Scattering William Henry Bragg (1862-1942) William Lawrence Bragg (1890-1971) Incident X-rays are both transmitted and reflected from each atom in a crystal. Waves reflected from each lower plane must travel an extra distance of r = 2 d cos θ before joining those reflected from the upper plane William and Lawrence Bragg studied how X-rays are reflected from crystals.
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10/06/09 Physics 2212 - Lecture 5 Bragg Scattering (2) The Braggs developed a way of producing a beam of X-rays and shining them on a rotatable crystal, and them measuring the angles at which intensity maxima were observed. They developed the Bragg relation describing the conditions under which maxima occur.
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This note was uploaded on 06/07/2009 for the course PHYSICS 2212 taught by Professor Geist during the Fall '09 term at Georgia Perimeter.

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Phys2212_24.1+to+24.5 - Physics 2212 Waves Lecture 5 Waves...

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