In order to better observe the discrete quantized energy levels, a high voltage is needed to accelerate the electrons. This means the high voltage supply is used to amplify the signal output from the function generator. In this experiment, the high voltage device amplified the voltages by 20V. Because the high voltage device amplified the linear voltage ramp function generator voltage by 20 voltages, the function generator had a voltage set between 0 and 4V so that the output voltage would remain between 0 and 80V. And as shown in Fig. \ref{fig:DCPowerSupply}, the high voltage output is applied between the cathode and accelerating plate to give the electrons enough energy. And another set of output leads would be put into a multimeter to measure the accelerating voltage.

When measuring the anode output, a low noise current preamp (Stanford Research Systems Model SR570) is used to amplify the small currents. The low noise preamp amplifies the small currents generated by the Franck- Hertz experiment. Using the amplified signal, the preamp then converts the signal to a voltage. In addition, the preamp is also used to clean up the signal by stabilizing the anode voltage (Not true: what is measured is a current, not a voltage. The input to the anode (and hence to the preamp) is a current. THe preamp measures the current and outputs a voltage that is proportional to the current). It does so by applying a 12dB low pass filter that allows us to filter out the unwanted frequencies.

To recap the two voltages that are being measured, there is the anode voltage which measures the electrons hitting the last plate in the tube and there is the accelerating voltage that measures the voltage applied to the system.

NOT TRUE: only one voltage is being physically measured: the accelerating voltage for the electrons. The other quantity being measured is a current: the electron current from cathode to anode. You are confusing what is measured in your apparatus — the Frank hertz tube — with what is RECORDED by the computer. Just because the output of an instrument that you measure with a computer happens to be a voltage doesn’t mean that what the instrument measured was a voltage. according to the table below, if the computer recorded a voltage of 1 V, then it meant that the cathode to anode current that was measured was 5 nA

In order to obtain more information on the quantum nature of atoms, the anode current plotted against the accelerating voltage would provide a general idea of the excited energy levels.