®
Model No. AP-8210A
-Introduction
012-13093B
3
Substituting equations ( 7 ) and ( 8 ) into equation ( 6 ) and rearranging yields:
The terms in the first set of brackets need only be determined once for any particular apparatus. The second term is
determined for each droplet, while the term in the third set of brackets is calculated for each change of charge that
the drop experiences.
The definitions of the symbols used, together with their proper units for use in equation ( 10 ) are:
q
– charge carried by the droplet
d
– separation of the plates in the droplet viewing chamber
– density of oil
g
– acceleration of gravity
– viscosity of air
b
– constant, equal to 8.13 × 10
-8
N/m
p
– barometric pressure
a
– radius of the drop in cm as calculated by equation ( 5 )
v
f
– velocity of fall
v
r
– velocity of rise
V
– potential difference across the plates in
Note
: The accepted value for e is 1.60 x 10
-19
coulombs
--------------------------------------------------
*For additional information about Stoke’s Law, please refer to Introduction to Theoretical Physics, by L. Page
(New York, Van Nostrand), Chapter 6.
**A derivation can be found in The Electron by R.A. Millikan (Chicago, The University of Chicago Press), Chap-
ter 5.
q
4
d
3
---------- 1
g
------ 9
2
------
3
1
2
---
1
1
b
pa
------
+
---------------
1
2
---
v
f
v
r
v
f
+
V
------------------------
( 10 )
=