Millikan Oil Drop Apparatus
Equipment
®
12
012-13093B
Suggested Procedure for Computation of the Charge of an Electron:
1.
Use the following equation to calculate the radius,
a
, of the oil drop:
2.
Substitute the radius,
a
, from the above equation to find the mass,
m
, of the oil droplet:
3.
Substitute
m
from the calculation above into the equation for computing the charge of an electron:
Using a Projecting Microscope with the Millikan Oil Drop Apparatus
To demonstrate Millikan’s experiment for an entire classroom on a TV screen or computer monitor, use a project-
ing microscope such as the Ken-A-Vision VideoFlex Microscope (PASCO Model SE-7227).
Procedure
1. Put a white paper screen in the droplet viewing
chamber to reflect more light:
a. Prior to focusing the viewing scope (see
Equipment
Setup
section,
Aligning the Optical System
), place
a white paper screen in the droplet viewing chamber
as illustrated in Figure 10.
b. Proceed with step 1 of
Aligning the Optical System
.
2. Align and focus the projecting microscope
:
a. Set up the projecting microscope as directed in the
manufacturer’s instructions.
b. After completing the setup and focusing of the Mil-
likan Oil Drop Apparatus on the oil droplets, care-
fully slide the eyepiece of the projecting microscope
over the eyepiece of the Millikan Apparatus.
c. Focus the projecting microscope as directed in the
manufacturer’s instructions.
a
b
2
p
------
2
9
v
f
2
g
-----------
+
b
2
p
------
–
=
m
4
3
---
a
3
=
m
4
3
---
b
2
p
------
2
9
v
f
2
g
-----------
+
b
2
p
------
–
3
=
q
mg v
f
v
r
+
Ev
v
----------------------------
=
q
4
3
---
g
b
2
p
------
2
9
v
f
2
g
-----------
+
b
2
p
------
–
3
v
f
v
r
+
Ev
f
---------------
=
Figure 10: Place a white paper screen in the
droplet viewing chamber.
1. Cut a 32 by 6
mm strip of white
paper and bend
back tabs of 6 by
6 mm.
2. Place the
paper screen so
the light path is
not blocked and
so the light is
reflected towards
the viewing
scope.
light path
paper
screen
spacer
viewing
scope
cross-section of
the droplet
chamber housing
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