In the Cathode Ray Experiment used to discover the electron,

(This is what my textbook says (Grade 11) so if there's any additional parameters that I do not know of I apologize)

The cathode ray tube has two electrodes and a evacuation. Under low pressures when high voltage is passed through the Electrodes, a stream of particles can be seen. Its presence was further confirmed by perforating the anode and by adding a phosphorescent coating of Zinc Sulphide behind it.

My question is since the anode is perforated will we see deflection of electrons towards the edges of the perforations because the eletrons tend to flow towards the anode so i see no reason for it to pass through the holes instead of deflecting towards the perforation boundaries.

Diagram to visualise what i mean :

Electrons flow into the anode to complete the circuit

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    $\begingroup$ This is because electrons possess very high speeds in the cathode ray tube and cannot be stopped suddenly. $\endgroup$
    – Infinite
    Apr 2, 2022 at 17:32
  • 1
    $\begingroup$ Yes, the field lines bend some near the holes. That is a small perturbation on the electron trajectory. $\endgroup$
    – Jon Custer
    Apr 3, 2022 at 15:36

1 Answer 1


I gather you are talking about the canal ray experiment rather as shown in the picture. In the canal experiments, positive charges pass through the hole when there is a reasonable number of gas particles.

The electron was not discovered with the perforated cathode experiments. These tubes were highly evacuated. The "electrons" (unknown at that time), were studied with tubes like these (https://virtuelle-experimente.de/en/e-feld/geschwindigkeit/geschwindigkeit.php):


This virtual experiment shows that the single hole in this diagram is indeed positively charged and one may ask why electron just get absorbed in it? The key point that you remember is that the voltage difference, although it looks like a small battery, is actually several thousand volts.

If the acceleration voltage different between the anode and the cathode is $V$, you can determine the velocity of electrons $v$ as

$v = \sqrt{ \dfrac{2 V e}{m} }$

Now $e/m$ is a huge number for electrons, and $V$ is large, so you can imagine that the electrons are directionally moving with a very very high velocity. Note a negatively charged cylinder over the coil. That coil also keeps the electron in the centered path.

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    $\begingroup$ Your explanation is correct. But it is not an answer to the question. As far as I understand, the question was : Why do the electrons cross the holes of the anode and are not deflected so as to touch the edge of the hole ? In my opinion, this phenomena is due to another anode, situated further away. $\endgroup$
    – Maurice
    Apr 3, 2022 at 9:52

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