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While studying about the anode ray experiment (E. Goldstein), I had a doubt pop up in my head. In the experiment, a perforated cathode has been used. What is the exact reason behind that? Upon spending some time over the net I've mostly come across the answer that it increases the surface area. Is there any other, more fulfilling answer to this? Why was such an electrode not used for the cathode ray experiment?

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  • $\begingroup$ It is flattering you prefer for this topic chemists to physicists. $\endgroup$
    – Poutnik
    Commented May 14 at 18:08

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Between the two plates, there is an electric potential. Since the tube is almost evacuated, charged particles can be accelerated and eventually travel across space with less chance to be discharged, than it were in air at atmospheric pressure. If the target were solid (similar to the solid anode in a conventional X-ray tube), the particles would hit this surface and «only» discharge there (and cause Bremstrahlung). Think of snow balls hitting a wall.

Here it is different, as some electrons accelerated are not caught and pass the mesh. They then can excite the few molecules still present in the back of the cathode. The English edition of Wikipedia contains the following illustration:

enter image description here

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    $\begingroup$ Thanks for the wonderful answer. Could you please elaborate on why this isn't required in the case of cathode rays? I couldn't understand that quite well. $\endgroup$
    – entropy
    Commented May 14 at 15:39
  • $\begingroup$ @entropy Cathode rays are the result of discharging electrons on gas molecules (thus, i) light is seen already between anode and cathode, ii) there can be multiple/different sorts of charged molecules generated). Anode rays are the result of electron impact on the surface of a solid target (hence reference to the conventional X-ray tube, though I presume today it equally could be a liquid (microfocus / molten metal jet X-ray tube), too). $\endgroup$
    – Buttonwood
    Commented May 15 at 16:16
  • $\begingroup$ Right, thanks a lot. Makes a lot more sense now. Thanks for the time and effort. $\endgroup$
    – entropy
    Commented May 15 at 17:43

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