Why canal rays need a perforated cathode?

[ananthu]

In the cathode ray production experiment, at about .01 mm of Hg, cathode rays travel from cathode and move towards anode and produce fluorescence on the walls near the anode.At the same time canal rays also move towards cathode. But only when you use a perforated cathode, the canal rays penetrate through it and produce fluorescence at the back of the cathode. I have doubts on the following aspects of the above experiment.
We are not using any perforated anode in the case of cathode ray production. Still these rays are able to produce fluorescence on the walls near the anode, thus indicating their presence. But why, the canal rays or the anode rays, so to speak, do need a perforated cathode to reach the other side and produce glow on the fluorescence screen kept at the back of the perforated cathode? Can not the anode rays make the walls near the cathode, glow even without a perforation in the cathode, as the cathode rays did?

As I am not able find the reason for it, it will be of great help to me if some experts on the subject throw some light on this aspect.

 

[UltrafastPED]

Canal rays are positive ions, while cathode rays are electrons or other negative ions.

None of them make it through if there are no holes ... the anode and the cathode are usually much too thick for particles to pass through; even a micron is too thick!

The fluorescence you see on the walls is from scattered electrons; they are much lighter than the positive ions, and hence scatter much more easily.

 

[ananthu]

Thanks for the reply.Sorry for my delayed response.

Canal rays are positive ions, while cathode rays are electrons or other negative ions.

The fluorescence you see on the walls is from scattered electrons; they are much lighter than the positive ions, and hence scatter much more easily.

Regarding the above statement, I could understand the light rays being scattered by an object. But how does it happen in the case of cathode rays? The latter being negative, when they hit the positive anode, will they not be attracted towards or absorbed by the anode rather than getting scattered?

 

[UltrafastPED]

Depends on the energy - if the particle energy is low enough there will be minimal scattering - but as the particle energy increases more and more scattering will be observed.

 

[pmacias]

The reason why canal rays need a perforated cathode is because they are a different type of ray compared to cathode rays. Canal rays are positively charged ions, while cathode rays are negatively charged electrons. When a high voltage is applied to the cathode, it emits electrons which travel towards the anode. These electrons create a vacuum in the glass tube and collide with the gas molecules present, causing them to emit light. This is the fluorescence seen on the walls near the anode.

However, canal rays are not emitted from the cathode. They are produced by ionizing gas molecules using a strong electric field. These ions are then attracted towards the cathode, but due to their positive charge, they cannot pass through the solid metal surface of the cathode. This is why a perforated cathode is needed - to allow the positively charged canal rays to pass through and reach the other side.

In addition, the anode in this experiment is not perforated because it is not needed for the production of canal rays. The anode is simply used to provide a positive charge and attract the canal rays towards the cathode. The fluorescence seen on the walls near the anode is a result of the interaction between the canal rays and the gas molecules in the tube.

I hope this explanation helps to clarify why a perforated cathode is necessary for the production and observation of canal rays. It is important to note that each type of ray behaves differently and requires specific conditions for their production and detection. As scientists, it is our job to continue exploring and understanding these phenomena.