User's Manual

Franck-Hertz Experiment Sample Data 2: Using a PASCO Interface
21
012-14264A
Use both. The average of the accelerating voltages matching peak positions and the valley positions is the voltage for the
approximate excitation energy, e•U
0
.
2. Why are the peaks and valleys smeared out rather than sharp?
The shape of the peaks and valleys in the curve is affected by the fact that there is a potential drop of 1.5 V at the cathode,
which is the source of the electrons. The cathode potential causes the peaks and valleys to occur over a space of 1.5 V, rather
than at a sharp point.
3. How precisely can you determine the peak/valley position? Explain and justify your estimates.
Note that the current fluctuations in the vicinity of the peaks, the width of the peaks, the steepness of the drop-off or rise, and
background height and shape all may play a role in this
4. How would molecular contaminants in the tube affect your results?
The molecular contaminant in the tube has a different first excitation potential (V
0
), so that the measurement of argon atom’s
first excitation potential would be affected.
Sample Data 2: Using a PASCO Interface
Filament voltage (V) = 3.55 V
V
G1K
= 1.5 V
V
G2A
= 11.0 V