In J. J. Thomson's cathode ray experiment, he used a discharge tube in order to make the gas inside conduct electricity.

Why do gases under low pressure conduct electricity?

  • 7
    $\begingroup$ Gases under high pressure can as well - see, e.g., lightning. All a question of the electric field, ionization potential, and mean free path of the electrons. $\endgroup$ – Jon Custer Sep 30 '16 at 16:46
  • $\begingroup$ highly related: chemistry.stackexchange.com/questions/37004/… $\endgroup$ – orthocresol Sep 30 '16 at 18:59
  • 2
    $\begingroup$ I think @ Jon Custer is correct. I suspect cathode ray tubes are mostly evacuated to allow the electrons a relatively unimpeded path. $\endgroup$ – bpedit Sep 30 '16 at 19:16
  • $\begingroup$ In a microwave oven, hot air at atmospheric pressure conducts nicely: youtube.com/watch?v=5f46zUgYBKE $\endgroup$ – DrMoishe Pippik Oct 2 '16 at 2:28

The cathode ray tube doesn't conduct electricity per se. It liberates free electrons that are simply moving through a vacuum from one end to the other. In practice, you can't create a real vacuum, so a low pressure gas (as low as possible) is used instead.

Air has a high enough dielectric strength that it will dampen the effect of the applied voltage. That is, it'll be harder to liberate free electrons to shoot down the tube.

| improve this answer | |

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.