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®
Model No. AP-8209
Photoelectric Effect Apparatus
10
6.
Replace the 365 nm filter with the 405 nm filter.
7.
Uncover the window of the Mercury Light Source. Spectral lines of 405 nm wavelength
will shine on the cathode in the phototube.
8.
Adjust the VOLTAGE ADJUST knob until the current on the ammeter is zero.
9.
Record the
magnitude
of the stopping potential for the 405 nm wavelength in Table 1.
10.
Cover the window of the Mercury Light Source.
11.
Repeat the measurement procedure for the other filters. Record the
magnitude
of the
stopping potential for each wavelength in Table 1.
Calculating
1.
Plot a graph of Stopping Potential (V) versus Frequency (x 10
14
Hz).
Note:
For information on using the DataStudio program to plot the graph, see
Appendix B.
2.
Find the slope of the best-fit line through the data points on the
Stopping Potential (V) versus Frequency (x 10
14
Hz) graph.
Note:
The slope is the ratio of
h/e
, so Planck’s constant,
h,
is the product of
the charge of the electron (e = 1.602 x 10
-19
C) and the slope of the best-fit
line.
According to the theory of linear regression, the slope of the Stopping Potential versus Frequency
graph can be calculated using the following equation:
where , , ,
and
.
3.
Record the calculated slope and use it to calculate the value of Planck’s constant,
h
.
Table 1: Stopping Potential of Spectral Lines, 4 mm diameter Aperture
Item
1
2
3
4
5
Wavelength,
λ
(nm)
365.0
404.7
435.8
546.1
577.0
Frequency,
ν=
c
/λ
, (x 10
14
Hz)
8.214
7.408
6.879
5.490
5.196
Stopping Potential,
V
(V)
slope
ν
V
ν
V
⋅
(
)
–
⋅
ν
2
ν
2
–
----------------------------------
=
ν
1
n
---
ν
i
i
1
=
n
∑
=
ν
2
1
n
---
ν
i
2
i
1
=
n
∑
=
V
1
n
---
V
i
i
1
=
n
∑
=
ν
V
⋅
1
n
---
ν
i
V
i
⋅
i
1
=
n
∑
=
Note:
DataStudio allows
you to enter your data as
ordered pairs in a Table
display and then plot the
data in a Graph display.