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History 181B: Modern Physics
Class 14 (2/21/03)
New radiations, new phenomena (2)
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| Outline |
Radioactivity (1896): What is going on?
What is the source of the energy?
Messy chemistry: More than one radioactive source
The explanation: Transmutation (1902)
Radioactive decay: A statistical process
The nature of the cathode rays
Aetherial disturbances or particles carrying charge?
Work left to be done
Theoretical: Lorentz's EM
field theory
Experimental: Properties
of the rays
J. J. Thomson and the electron (1897)
Cathode rays as particles
carrying charge
Measuring the properties
of these particles
What are these little pieces
of matter?
Reflections on confusion and complexity |
| Names
and terms |
| Primary |
Secondary |
Ernest Rutherford (1871-1937), NP
Chemistry 1908
Frederick Soddy (1877-1957), NP 1921
transmutation, decay
decay series
half-life
Heinrich Hertz (1857-1894)
H. A. Lorentz (1853-1928), NP 1902
electron
Philipp Lenard (1862-1947), NP 1905
J. J. Thomson (1856-1940), NP 1906
Cavendish Laboratory (Cambridge)
charge-to-mass ratio e/m
corpuscle |
N = N0 exp
(-t/t0)
Lorentz force law: F = qE + q
v x B
electrolysis |
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| Assignment |
J.J. Thomson, "Cathode Rays," Philosophical
Magazine 44 (1897): 293-316, also on the web
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Read pp. 293-297, skip pp. 298-307 if you like, pick
up on p. 307 with the paragraph beginning "Before proceeding . . ." and
read through p. 314, then skip the rest of you like.
What was the point of Thomson's first experiment
(shown in Fig. 1)? Why was it necessary?
Work through Thomson's account of how the apparatus
depicted in Fig. 2 functions. Then see what he used it to measure following
the argument on pp. 307-308.
What were Thomson's central conclusions about the
nature of the carriers on p. 310?
Thomson's discussion on pp. 311-314 connects the
carriers to atoms and to matter. What strikes you as unexpected about his
account?
Extra: What is going on in the sections you
don't have to read? Where does it fit in the standard account of Thomson,
discoverer of the electron? |
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Copyright © Cathryn Carson 2003 |