User's Manual

SE-9639 Franck-Hertz Experiment
12
012-14264A
Manual Measurements
1. Increase the accelerating voltage V
G2K
by a small amount (for example, 1 V). Record the new accelerating voltage V
G2K
(value read on voltmeter) and current I
A
(read on “Ammeter”) in Table 1:1. Continue to increase the voltage by the same
small increment and record the new voltage and current each time in Table 1:1. Stop when the accelerating voltage V
G2K
= 85V. (If the current I
A
exceeds the range, reduce the filament voltage (for example, 0.1V) and start over again.)
2. Try to identify the “peak positions”, i.e. watch for those values of the accelerating voltage V
G2K
for which the current
reaches a local maximum and begins to drop on further increase of the accelerating voltage. Take a few data points (V
G2K
,
I
A
) around these peak positions and record them in Table 1:2. Try to identify the “valley positions”, i.e. watch for those
values of the accelerating voltage V
G2K
for which the current reaches a local minimum and begins to rise on further
increase of the accelerating voltage. Take a few data points (V
G2K
, I
A
) around these valley positions and record them in
Table 1:2.
3. Take sufficiently many voltage values so as to allow you to determine the positions of the peaks and valleys.
Table 1.1: Accelerating Voltage and Tube Current
Table 1.2: Peak and Valley Voltages
Analysis
1. Plot the graphs of Current (y-axis) versus Voltage (x-axis).
V
G2K
(V)
I
A
(x 10
-10
A)
V
1
V
2
V
3
V
4
V
5
V
6
Peak
positions
V
G2K
(V)
I
A
(x 10
-10
A)
Valley
positions
V
G2K
(V)
I
A
(x 10
-10
A)
Note:
• During the experiment, pay attention to the output current ammeter when the voltage is over 60 V. If
the ammeter’s reading increases suddenly, decrease the voltage at once to avoid the damage to the
tube.
• If you want to change the value of V
G1K
, V
G2A
and V
H
during the experiment, rotate the “0 ~ 100 V”
adjust knob fully counter-clockwise before making the changes.
• The filament voltage is tunable from 0 to 6.3V. If the anode output current is too high and causes the
amplifier to overflow, the filament voltage should be decreased.
• As soon as you have finished the experiment, return the V
G2A
voltage to 0 V to prolong the life of the
argon tube.