‘
,
18
-
1.
THE CHARGE OF THE ELECTRON
fall over a given number of divisions. Remember that the micro—
.
.
scope
inverts the motion.
Repeat no less than twenty-ve times.
,
The values of the electric eld and of the chargeon the drop are
immaterial.
…
11. Adjust the electric eld until the drop does not move up
or down. °If the charge or the voltage changes, re—balance. The
voltage and charge do not enter into the calculations. Turn the
microscope so that its scale is horizontal, i.e., the graduations are
vertical.
The drop Will be seen
to shift horizontally, back and
forth.
Record its position on the scale at regular _intervals of,
',
say 30 sec0nds_ (=z‘), until at least one hundred readings have
,
‘
been taken.
'
'
Calculatiom.—12. Average the times of fall and compute the
velocity of fall vd. Compute the radius of the drop, using equa—
tions 1—22 and 1—23.
(These equations might also have been
,
used in.the determination of the charge of the electron.)
13. Take differences (=s) between the successive scale positions of the drop in (11). Square each value and then average
(=Î2). Multiply by the square of the number of centimeters cor—
responding to each divisionbf the scale (=k2). Then, Ïcî =
These are the avérage-squared Brownian displacements in the x“
directi0n in the time :.
If a very large number of individual displacements : have.been observed a suiciently accurate value is
._
given by Î2 =
14. Calculate N from equation «1—21 and comparé with the
_
accepted value.
_
,
_
'
*
\
,
'
'
.
…
_
.
_
REFERENCES
;
'
'
1Se€z‘âë€ral
belOW…
'…
'
-
-
'
.
_
_
*
2K11tm
682 (1935)… W- N. Bond, Phil. Ma-g zz,
631(1936) ISh1da,
Suetsugù, fN‘atùre, 140, 29
(1937) W VHOUSËOH: “PhYS—‘ReV-ÏSZQ 751 (1937), nde‘ (at
.
23C>=18292><10Wth thMkldpdt *thi‘s‘
*Ff; Ü>
_
,
.
by -
“
-
‘
FletCherœmeawreNeandN See,PhY$Rev33,81(1911),