Franck Hertz experiment - overheated tube

[wavingerwin]

Homework Statement

What happens when the tube is (a) overheated or (b) too cool.

Homework Equations

The Attempt at a Solution

I searched on google and almost all said:

"
If the tube has been overheated, the emission current is small, and maxima and minima can hardly be recognized or seen at all ... On the other hand, when the tube is not sufficiently heated, the emission current is large and the maxima, especially those of a higher order, can hardly be seen. This is because, due to the low mercury pressure in the tube, discharge can place even at small voltages. When this is the case, the tube must be heated to a higher temperature.

"

I am struggling to understand this. What is the emission current? Is it the current of electrons flowing from the cathode? And I also don't get why would maxima/minima can hardly be seen if this current is small/large.

Please explain and thanks in advance

 

[mark726]

.

I can provide some insight into what happens to the tube when it is overheated or too cool.

Firstly, the emission current refers to the flow of electrons from the cathode to the anode within the tube. This current is crucial for the functioning of the tube, as it allows for the production of light and the detection of the spectral lines.

When the tube is overheated, the emission current is small. This means that there is not enough energy for the electrons to be emitted from the cathode. As a result, the spectral lines become faint or even disappear, making it difficult to observe the maxima and minima. This is because the electrons are not able to excite the atoms in the gas within the tube, leading to a decrease in the intensity of the spectral lines.

On the other hand, when the tube is too cool, the emission current is large. This means that there is too much energy for the electrons to be emitted from the cathode. As a result, the spectral lines become too intense, making it difficult to distinguish between the maxima and minima. This is because the excess energy from the electrons can cause multiple excitations within the gas atoms, leading to a broadening of the spectral lines.

In summary, in order for the tube to function properly and for the maxima and minima to be clearly observed, the tube needs to be heated to a specific temperature where the emission current is just right. Too much or too little heat can lead to difficulties in observing the spectral lines. I hope this helps to clarify the concept of emission current and its effects on the tube.