Why does Frank Hertz's experimental curve change periodically?

With the increase of electron energy, electrons and mercury atoms alternately collide elastically and inelastic, and the peak represents elastic collision, so the energy loss is less, the current is greater, and the energy decreases significantly after crossing the threshold.

In the mercury-filled F-H tube, electrons are emitted from the hot cathode, and the accelerating voltage UG2K between the cathode K and the second grid G2 accelerates the electrons. The first grid plays a buffering role in electron acceleration to avoid damaging the cathode when the acceleration voltage is too high. A reverse repulsive voltage UpG2 is applied between the plates P and G2. When electrons pass through KG2 space, if the energy is larger (≥eUpG2), they can rush through the reverse repulsive electric field and reach the flat plate, forming a flat plate flow, which is detected by the micro-galvanometer pA.

Extended data:

Precautions:

The experimental device adopts 220V AC single-phase power supply, and the grounding wire in the incoming line of the power supply should be in good contact to prevent interference and ensure safety.

The negative terminal of the X input of the function recorder cannot be connected with the negative terminal of the Y input, nor can it be connected with the ground wire (⊥) of the recorder, otherwise the instrument will be damaged.

If ionization breakdown occurs during the experiment (that is, the ammeter is seriously overloaded), the accelerating voltage should be reduced to zero immediately. So as not to damage the pipeline.

The shell temperature of the heating furnace is high, so handle should be used carefully when moving, and wires should not lean against the furnace wall to avoid scalding and softening of plastic wires.

Baidu Encyclopedia-Frank-Hertz Experiment