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Lect_34_note - Chapter 40-42 Introduction to Quantum Physics Models of the Atom Democritus a fifth century B.C Greek philosopher proposed that all

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Chapter 40-42 Introduction to Quantum Physics
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Models of the Atom z Democritus, a fifth century B.C. Greek philosopher, proposed that all matter was composed of indivisible particles called atoms (Greek for uncuttable). z Billiard Ball Model (1803)- John Dalton viewed the atom as a small solid sphere.
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Joseph John Thomson z Received Nobel Prize in 1906 z Usually considered the discoverer of the electron z Worked with the deflection of cathode rays in an electric field z Opened up the field of subatomic particles 1856 – 1940, English
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J.J. Thomson’s Experiment at 1894 z q V = mv 2 /2 z v = E / B z q/m = (E / B) 2 /(2 V ) Thomson’s experiment did show that the stream consists of separate and negatively charged particles, all having the same definite mass which is much smaller than the slightest atom. So, atoms are not uncuttable.
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Thomson’s Models of the Atom z A volume of positive charge z Electrons embedded throughout the volume z Plum pudding model
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Rutherford’s Experiment in 1911 z A beam of positively charged alpha particles hit and are scattered from a thin foil target Ernest Rutherford 1871-1937 New Zealand
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Rutherford’s Experiment: Expected Results + + JAVA
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Rutherford’s Experiment : Striking Results A small fraction (about one in ten thousand) rebounded, ending up on the same side of the foil as the incoming beam. A few were returned almost along the same tracks as they went in. + +
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Rutherford’s Experiment : Striking Results Rutherford described this result as the most incredible event of his life. He said, " as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you ." +
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Rutherford’s Experiment : Explanation Such huge deflections could mean only one thing: some of the alpha particles had run into massive concentrations of positive charge and, since like charges repel, had been hurled straight back by them.
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This note was uploaded on 01/28/2011 for the course PHYS 011 taught by Professor Nianlin during the Fall '08 term at HKUST.

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Lect_34_note - Chapter 40-42 Introduction to Quantum Physics Models of the Atom Democritus a fifth century B.C Greek philosopher proposed that all

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