3B SCIENTIFIC PHYSICS 1000620 Instrucciones De Manejo página 15

Fig.8 Example curve recorded with the control unit for the Franck-Hertz experiment
7.3.3 Calibration of measurement curve
• Set the heater voltage to 3.5 V and collector
voltage to -1.5 V; set the lower limit for the
accelerating voltage to 0 V and the upper
limit to 60 V. Turn up the gain.
The oscilloscope screen shows a curve which has
a weakly defined structure in three places. The first
of these structures are of interest here. To empha-
sise these places, carry out the following proce-
dure.
• Reduce the upper limit of the accelerating
voltage down to about 35 V.
This zooms in on the measurement curve and
the structures become clearer.
• In order to display the curve even bigger,
raise either the gain or the heater voltage.
You may need to change the oscilloscope
settings.
• Raise the upper limit of the accelerating
voltage (to about 15 V) until the curve starts
at the edge of the first peak. You may need
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•
The range of the curve in which the critical po-
tentials lie is now displayed within clearly de-
fined limits on the oscilloscope screen and the
critical potentials themselves can specifically be
identified.
Technical amendments are possible
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to increase the gain to display the structures
better.
Reduce the upper limit of the accelerating
voltage (to about 20 V) until the curve ends
at the point where ionisation begins.