Question :

We were recently studying the chapter on Atomic Structure and we had a topic about cathode rays and the single particle of a cathode ray is called cathode ray particle.

The next topic was about +ve rays / canal rays and there was a discharge tube diagram showing the creation of positive rays and the diagram showed positve rays emitting from anode which is the expected thing (since cathode rays emit from cathode).

Our class teacher told us that the diagram was wrong and that positive rays don’t emit from anode and also they aren’t called anode rays.

Now I am confused whether my teacher is right or wrong. If he is right then what is the reasoning behind this

Teacher’s answer :

This is what our teacher told us :

positive rays are not called anode rays because they unlike cathode rays (which originate from the cathode) these are not produced by the anode.

Origin :

These are produced by ionization of atoms or molecules of residual gas when bombarded with cathode rays.

Equation :
$$ \ce {e}^{-} + M → \ce {M}^{+} + \ce {e}^{-} + \ce {e}^{-} $$

  • 1
    $\begingroup$ Cathode rays and anode rays are quite different things. $\endgroup$ – Ivan Neretin May 23 '18 at 11:52
  • $\begingroup$ @IvanNeretin : OOPs. That was a mistake on my part, updated $\endgroup$ – Muhammad Salman May 23 '18 at 11:58

Your teacher was absolutely right, because anode rays are not generated from anode.

They are the result of fast-moving cathode rays that strike the gas molecules. They knock out electrons from gas molecules and thus become positive ions which start moving towards the cathode.

They are called positive rays due to their positive charge and canal rays as they were passed through a perforated cathode or canal.


Your teacher was wrong (or you misunderstood).

Anode rays = positive rays = canal rays, and they come out of anodes.

See the Wikipedia article on anode rays.

The whole business is tricky to memorize because long before you were born, people defined the charge of electrons as negative. This is how I remember my definitions:
(1) Electrons are negatively charged.
(2) Cations are positively charged. Remember that cats are cute and furry and cuddly, which is a positive thing.
(3) Cations are attracted to cathodes. Anions are attracted to anodes. That's why they are called that. So the electrodes have charges opposite to the ions they attract: anodes are positive (not enough electrons), cathodes are negative (too many electrons).
(4) Particles that leave an electrode do so because they have the same charge and are repelled. Anodes make positive particle beams, cathodes make negative particle beams.

I can't tell if the diagram you were given is wrong without seeing the diagram...

  • $\begingroup$ I can’t show the diagram it is on my book $\endgroup$ – Muhammad Salman May 23 '18 at 12:43
  • $\begingroup$ "Anion = A Negative Ion" works better for me, even though I do think cats are a positive thing (amber vs cat fur included). $\endgroup$ – Jon Custer May 23 '18 at 13:09
  • 1
    $\begingroup$ "Cat-ions are purrsitive" is how I remember it. Although I probably shouldn't. $\endgroup$ – AndyW May 23 '18 at 13:47
  • $\begingroup$ Positive rays don't come out of anodes, it just looks that way. They are generated in the gas from gas molecules not from the anode. $\endgroup$ – matt_black May 29 at 11:17

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