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CHAPTER 2.
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THE MASS OF THE ELECTRON
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2—1.
Cathode Rays—Connect
of an induction
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coil to two metal. electrodes sealed in a glass tube, as in gure 2—l,.
and study the passage
of electricity between them as the air is
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gradually removed. A point will be reached, at pressùres
around
ODS—0.005 mm. of mercury,
Where
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B. _
a
greenish Or bluish uorescence
appears on the walls of the tube
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and a faint streak of light may be
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FIG. 2—1.
To study cathode rays.
coming
the
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electrode.
Many interesting phe7
nomena may now be observed.
For example, a solid object at X
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casts a shadow on the walls at B.
Since the edges of this shadow
are clean cut, the rays which cause the glass to uoresce must have
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travelled in straight lines from the cathode. If a concave cathode
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is used, the rays come to a focus, where they may melt a piece of
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metal foil. This shows that they leave the cathode perpendicu—y
lady-and
great energy.
they strike a light,carefully
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pivoted paddle
they cause it torotate, showing that they
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have inertia or mass.* Then it must be true that they have either *
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great mass or high velocity. —»
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These “cathode rays” can be deected by an electric or mag—
'netic eld. Hence, they consiSt of electrical charges in motion.
F r0inthe direction in which the rays are deected, their charge
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Ï found
to be negative. This has
by catChing_thenï in—
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metal cup
Chamber)
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electrometer.
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If a thin aluminum window is used inSteaid of the glass at
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gure 2—1, cathode-rays
will be found to _emerge- into the
These
._* This
is usually performed in a tube containing a moderate amount
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of gas… The paddle wheel is then; set‘into rotatiOn by theheat caused by the
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bombarding
as in Cr'ookès’ radiometer,»‘and
effect discuæed is masked.
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Ahigh‘degree0f evacuation‘ should be used; ;
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