2
'
1.
THE CHARGE OF THE ELECTRON
charged particles,
called “ions,” and appear
as
a
cloud which
slowly settles to the bottom of the conta1n1ng chamber under
the
force of gravity.
The weight of this cloud Can be determined by
blowing it into a drying tube, Which is weighed before and after the
arrival of the cloud.
The average weight of one of the water drops
may
be estimated by observing the rate of fall of the top surface of
the cloud and applying StokeS’ theoretical law for the velocity of
fall of a small body through a gas. Dividing the total weight of
'
the cloud by the average
one drop then gives the total
number of drops in the cloud. This is also equal to the number
of charged particles, provided only one water drop forms on one
ion.
Next, the total electrical charge of the cloud is measured by
_
passing it into a chamber or allowing it to fall upon a metal plate
connected to a sensitive electrical instrument such as an electrometer.
the total charge by the number of ions in the cloud
gives the charge on each ion.
'
In 1897, Townsend used this method and found the charge of '
,
the electron to be a= 3.4 X 10”10 e.s.u.
In 1903, H. A. Wilson
_
used this method with the addition of an electrical eld.
His
method is essentially that described in the next section, except
‘
that he used water
which evaporate during the experiment,
'
and that he made his measurements on the entire cloud instead of
_
on Â_a single drop. He found 6 = 3.1 X 10"10 e.s.u. Both of
these early values are of the right Order of magnitude only.
.
1—3._ The Oil—drop Method.——An accurate method of measur—
ing the charge of the electron was developed during the years 1909—
1913 by R. A.
He made many measurements of the
electrical charge on a single drop of oil located between the plates
»
d
"
_
,
_
e e,,
,
Î_'—
'
.
FIGH
drops. ,
‘
alwaysan1nœgralm“1üple
Oil was
,
usedt0Pæventbss°fW€1%htbYevaporatwn Th€0111s charged , *
'
1.
THE CHARGE OF THE ELECTRON
charged particles,
called “ions,” and appear
as
a
cloud which
slowly settles to the bottom of the conta1n1ng chamber under
the
force of gravity.
The weight of this cloud Can be determined by
blowing it into a drying tube, Which is weighed before and after the
arrival of the cloud.
The average weight of one of the water drops
may
be estimated by observing the rate of fall of the top surface of
the cloud and applying StokeS’ theoretical law for the velocity of
fall of a small body through a gas. Dividing the total weight of
'
the cloud by the average
one drop then gives the total
number of drops in the cloud. This is also equal to the number
of charged particles, provided only one water drop forms on one
ion.
Next, the total electrical charge of the cloud is measured by
_
passing it into a chamber or allowing it to fall upon a metal plate
connected to a sensitive electrical instrument such as an electrometer.
the total charge by the number of ions in the cloud
gives the charge on each ion.
'
In 1897, Townsend used this method and found the charge of '
,
the electron to be a= 3.4 X 10”10 e.s.u.
In 1903, H. A. Wilson
_
used this method with the addition of an electrical eld.
His
method is essentially that described in the next section, except
‘
that he used water
which evaporate during the experiment,
'
and that he made his measurements on the entire cloud instead of
_
on Â_a single drop. He found 6 = 3.1 X 10"10 e.s.u. Both of
these early values are of the right Order of magnitude only.
.
1—3._ The Oil—drop Method.——An accurate method of measur—
ing the charge of the electron was developed during the years 1909—
1913 by R. A.
He made many measurements of the
electrical charge on a single drop of oil located between the plates
»
d
"
_
,
_
e e,,
,
Î_'—
'
.
FIGH
drops. ,
‘
alwaysan1nœgralm“1üple
Oil was
,
usedt0Pæventbss°fW€1%htbYevaporatwn Th€0111s charged , *