_
_
2—2.
]. ]. THOMSON METHOD
21
Will travel for a distance of several centimeters.- They are then
called Lenard rays,1 after their discOverer, and are produced in
_
large quantities by the Coolidge cathode-ray
_
The motion of cathode rays may be studiedby the uorescence
they produce when they strike glass or a luminescent screen such
‘
as calcium tungstate, by the streak of light which they produce in
_
_
a gas through which they are passing, by metal collectors leading
_
to an electrometer, and by the blackening which they can produce
on a photographic plate.
’
,
Electrons emitted from a hot lament in a vacuum exhibit
these same properties. This indicates that cathode rays consist of
electrons.
They can be produced in a vacuum" tube regardless of
the gas used or the cathode material, so that they are a common
constituent of all matter.
It is also interesting to note that, since
they can pass through thin aluminum foil, they must be compara—
_tively small and the inter-atomic spaces of matter
com- ‘
paratively large.
_
-
…
-
-
When cathode rays are suddenly stopped by a solid body, they
-
_
set up X—rays much as the bullets of a machine gun striking a
target produce sound waves.
_
.
As the following experiments Will show, the velocity of these
electrons is great and their mass is very small.
A direct measure—
of their mass has never been made.
Instead, the ratio of
their charge to their mass, e/m, is measured and then,'from the
known charge 6, the mass may be calculated.
…
'_ ‘
__
_
'
2—2.
of ]. ]. Thomson to Measure=e/m.—In
1897, ]. ]. Thomson3 rst measured the ratio of charge to mass
‘
and the velocity(v) of cathode rays by bending them in a
'
combined electric and magnetic eld. As shown in gure 2—2,
‘
,a hot
is located- in a glass tube whichhas been well
It emits'.electr0ns, each of which has a mass of m
grams and carries a charge of (: electromagnetic units. . These are .
accèlerated toward a positively charged metal plate P and—some
.
-
pass through a smallhole with ,a velocity“ of
centimeters pe‘r'
secohd‘.‘
they pass straight ahead to *form a point of
_
light on the
S‘.
This screen consists of a glass plate
'
_' -‘coa_ted With a uorescentmat‘erial, such as willemi‘te, luminescent gl
-
calcium tùngstate or_zinc sulphide. If_ a uniform magnetic eld
.
strength H , oersteds is applied per'pèndicùlarily
: across the
-
_
2—2.
]. ]. THOMSON METHOD
21
Will travel for a distance of several centimeters.- They are then
called Lenard rays,1 after their discOverer, and are produced in
_
large quantities by the Coolidge cathode-ray
_
The motion of cathode rays may be studiedby the uorescence
they produce when they strike glass or a luminescent screen such
‘
as calcium tungstate, by the streak of light which they produce in
_
_
a gas through which they are passing, by metal collectors leading
_
to an electrometer, and by the blackening which they can produce
on a photographic plate.
’
,
Electrons emitted from a hot lament in a vacuum exhibit
these same properties. This indicates that cathode rays consist of
electrons.
They can be produced in a vacuum" tube regardless of
the gas used or the cathode material, so that they are a common
constituent of all matter.
It is also interesting to note that, since
they can pass through thin aluminum foil, they must be compara—
_tively small and the inter-atomic spaces of matter
com- ‘
paratively large.
_
-
…
-
-
When cathode rays are suddenly stopped by a solid body, they
-
_
set up X—rays much as the bullets of a machine gun striking a
target produce sound waves.
_
.
As the following experiments Will show, the velocity of these
electrons is great and their mass is very small.
A direct measure—
of their mass has never been made.
Instead, the ratio of
their charge to their mass, e/m, is measured and then,'from the
known charge 6, the mass may be calculated.
…
'_ ‘
__
_
'
2—2.
of ]. ]. Thomson to Measure=e/m.—In
1897, ]. ]. Thomson3 rst measured the ratio of charge to mass
‘
and the velocity(v) of cathode rays by bending them in a
'
combined electric and magnetic eld. As shown in gure 2—2,
‘
,a hot
is located- in a glass tube whichhas been well
It emits'.electr0ns, each of which has a mass of m
grams and carries a charge of (: electromagnetic units. . These are .
accèlerated toward a positively charged metal plate P and—some
.
-
pass through a smallhole with ,a velocity“ of
centimeters pe‘r'
secohd‘.‘
they pass straight ahead to *form a point of
_
light on the
S‘.
This screen consists of a glass plate
'
_' -‘coa_ted With a uorescentmat‘erial, such as willemi‘te, luminescent gl
-
calcium tùngstate or_zinc sulphide. If_ a uniform magnetic eld
.
strength H , oersteds is applied per'pèndicùlarily
: across the
-