Reasons why the Franck Hertz experiment might fail

In summary, during the Franck Hertz experiment with mercury vapour, intervals of 5.75 and 6.40 V were obtained for the excitation potential, while the expected intervals should have been at 4.9 V. The potentials were measured using an oscilloscope on convenient scales, but other possible factors that could have affected the results include a faulty tube or air in the mixture, the need for calibration of the oscilloscope, or issues with cables or grounding. It is also important to note that glass has capacitance and can accumulate charge, so precautions should be taken to avoid touching the tube during the experiment. Additionally, it is recommended to allow the filament to warm up before starting the experiment.
  • #1
sunrah
199
22
We conducted the Franck Hertz experiment with mercury vapour and got intervals for the excitation potential of 5.75 and 6.40 V. I know that the intervals should be 4.9 V.
The potentials were measured using an oscilloscope at the most convenient scales.

I just can't think what may have gone wrong other than faulty tube/air in mixture (although we should still see some intervals at 4.9 V I think?) or oscilloscope needs callibrating. The apparatus was allowed to heat up a good ten minutes before we started.

What else could have affected things?
 
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  • #2
Check your cables. Sometimes the solder joints to the plugs at the end of the cables break.

Check your grounding.

Glass has capacitance and can accumulate charge but any good company will usually coat their tubes will an extremely thin metallic film to dissipate it.

Because of the capacitance, don't let anyone touch the tube during the experiment.

Did you give the filament a little time to warm up?
 

1. What is the Franck Hertz experiment?

The Franck Hertz experiment is a classic physics experiment that demonstrated the quantization of energy levels in atoms. It involves passing electrons through a tube filled with gas and measuring the energy of the electrons after they collide with gas atoms.

2. What are some potential reasons why the Franck Hertz experiment might fail?

There are several reasons why the Franck Hertz experiment might fail, including incorrect setup or calibration of equipment, impurities in the gas, or external interference from electromagnetic fields.

3. How can incorrect setup or calibration of equipment affect the Franck Hertz experiment?

If the equipment used in the experiment is not set up or calibrated correctly, the measurements taken may be inaccurate and lead to incorrect results. This can include incorrect voltage settings, faulty connections, or malfunctioning equipment.

4. Can impurities in the gas affect the Franck Hertz experiment?

Yes, impurities in the gas can affect the Franck Hertz experiment by altering the behavior of the gas atoms and electrons. This can lead to incorrect energy measurements and potentially cause the experiment to fail.

5. How can external interference from electromagnetic fields impact the Franck Hertz experiment?

External interference from electromagnetic fields can disrupt the movement of electrons and gas atoms, leading to distorted results and potential failure of the experiment. It is important to conduct the experiment in an environment with minimal electromagnetic interference to ensure accurate results.

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