3B Scientific Teltron Critical Potentials Tube S with He-Filling - Manual (Page 3)

UE502050 3B SCIENTIFIC® PHYSICS EXPERIMENT
3B Scientific GmbH, Rudorffweg 8, 21031 Hamburg, Germany, www.3bscientific.com
© Copyright 2008 3B Scientific GmbH
Optimising the parameters:
•
Start the graph-plotting of the experimental data.
•
Set up the graph with “relative time t in s” on the x-axis and
the quantity I on the y-axis.
•
Repeat the measurements with slightly higher heater voltages
and different accelerating voltages, plotting the graph in each
case, to find the optimum heater voltage and optimum range
between the minimum and maximum accelerating voltages U
A
.
Calibrating the accelerating voltage:
•
In the spectrum, identify the 2 3 S peak at 19.8 eV and
determine its position t
1
on the time axis.
•
Identify the ionisation threshold at 24.6 eV and determine its
position t
2
on the time axis.
•
Enter a new formula for the quantity V defined as
19.8 + 4.8 * (t - t
1
)/(t
2
- t
1
); in this expression enter the
numerical values for t
1
and t
2
in ms determined as above.
•
Set up a graph with the quantity V on the x-axis and the
quantity I on the y-axis.
•
Re-start the plotting of the experimental data.
SAMPLE MEASUREMENTS AND EVALUATION
Table 1: Literature values of the critical potentials of helium
Term
E / eV
2 3 S 19.8
2 1 S 20.6
2 3 P 21.0
2 1 P 21.2
3 3 S 22.7
3 1 S 22.9
4 1 P 23.7
Ionisation 24.6
•
In the plot of the experimental data, identify the critical
potentials listed in Table 1 (see Fig. 4).
2 S 3
2 P 3
Ion
3 S 1
3 P 3
3 P 1
2 S 1
2 P 1
3 S 3 4 S 3
4 S 1
Fig. 4: Collector current I
R
as a function of accelerating voltage U
A