Abstract: In the Franck-Hertz experiment, the intensity of iYp-V varies with the temperature of the oven and the voltage of the filament. We find that the intensity of Ip-V signal decreases with the temperature when the tem-perature is below 160 ℃, and increases with the temperature when the temperature is higher than 170 ℃. We then introduce the model of thermal excitation and ionization, which explains such phenomenon when the law of thermal-dynamic equilibrium and the Le Chateler＇s law are applied. After that, we have designed some additional experi- ments, whose results support our postulation.

Key words: Frank-Hertz experiment, Ip-V signal, thermal ionization