How fast do CRTs shoot electrons?

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Discussion Overview

The discussion centers around the speed at which cathode ray tubes (CRTs) shoot electrons, specifically focusing on average speeds and the factors influencing them, such as voltage. The scope includes theoretical considerations related to electron acceleration and relativistic effects.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • Some participants assert that electrons must travel at speeds less than the speed of light due to their mass and special relativity.
  • One participant calculates that with a 400 V cathode voltage, electrons achieve an average speed of approximately 1.18 x 107 m/s, which is about 4% of the speed of light.
  • Another participant mentions that in larger tube TVs, the accelerating voltage can be around 25,000 Volts, suggesting that electrons could reach speeds of about one-third the speed of light using a non-relativistic approximation.
  • A participant acknowledges a mistake in their earlier voltage figure, indicating uncertainty about the correct voltage for CRTs.

Areas of Agreement / Disagreement

Participants generally agree that electrons cannot exceed the speed of light due to their mass, but there are differing views on the specific average speeds achievable in CRTs based on varying voltage levels. The discussion remains unresolved regarding the exact speed of electrons in CRTs.

Contextual Notes

The calculations provided depend on assumptions about voltage and do not account for relativistic effects at higher speeds, which may affect the accuracy of the proposed speeds.

Ralphonsicus
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Thanks.
 
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It must be less than the speed of light.
 
Yes I know that because electrons have mass and therefore (according to special relativity) they cannot reach light speed. But that wasn't the question, the question was HOW FAST do CRTs shoot electrons (on average)?
 
Ralphonsicus said:
Yes I know that because electrons have mass and therefore (according to special relativity) they cannot reach light speed. But that wasn't the question, the question was HOW FAST do CRTs shoot electrons (on average)?

With a quick bit of googling I found that the voltage of a CRT TV cathode is 400 V. Therefore an electron accelerated will obtain 400 eV of energy. The speed of an 400 eV electron is 1.18*10^7 m/s or ~4% of the speed of light.
 
Oops, don't know how I came up with 400 V. Maybe that's for a ye olde oscilloscope or something.
 
Haha it's grand, thanks all.
 

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