.
_
_
1—9.
AVOGADRO’S NUMBER
11
vertical.
Oil is sprayed into the 'Condenser and a small drop is
-
selected.
If the radins of the drop ”is suiciently small, say
10”5 cm., the Brownian movements
be readily observed.
The drop is balanced by so adjusting the potential of the battery
.
that the downward force of gravity is just counterbalanced by the
'
upward electrical force‘. The drop Will be seen to move back and
forth With Brownian motion in a haphazard fashion. The number
of 'centimeters x which it moves in the horizontal direction during
a given. time interval t, of say 30 seconds, is measured ”many times.
One may disregard the sign of the displacements (whether to the
left or to the right) since the individual values are to be squared.
The average of their squares is
in equation 1—19.
In order to determine the friction constant K, the corrected
form of“Stoke’s law, as given by equation 1—9 and the mass equa—
tion 1—6 are substituted in the force equation 1—1. Thus
_
…
.
K = —'
-
'
(1—20)
_
;
'
When sùbstituted in equation 1—19, this leads to
_
_
N :
Æ
.
_
(1…21).
_
'
6771
x2
_
a
_
"
R = 8.32 >< 107ergs'per degree;T = 273 + °C,ô = 6.17 X
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