Coloured beam in a discharge tube

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Why cathode rays which consist of electron that do not have any colour are seen as a colourful ray of light in a discharge tube??
 

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  • #2
berkeman
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Welcome to the PF.

Do you mean on the face of a Cathode Ray Tube (old-style television screen)? If so, phosphor coatings are used on the CRT faceplate to generate the colors...

http://qxwujoey.tripod.com/06crtmon.gif
06crtmon.gif
 

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  • #3
DrClaude
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The OP appears to be asking about discharge tubes, not CRTs. The answer is because the tube contains a gas, and it is that gas that emits the light upon excitation from electron impact.
 
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ZapperZ
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That means that we cannot see the cathode and anode rays without any phosphor coating?
Please read what DrClaude said. The discharge tube often has an inert gas!

Zz.
 
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I still can't understand please be more explanatory.....
 
  • #7
berkeman
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I still can't understand please be more explanatory.....
We are all saying that an electron beam traveling in a vacuum does not give off a color of visible light. The energy from the accelerated e-beam can be transferred to phosphor or to gas molecules to cause visible light to be given off.

Please use Google and our replies to do some more research on this topic, and report back here with links to your reading. Thank you. :smile:
 
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ZapperZ
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I still can't understand please be more explanatory.....
Electrons accelerates...... bump into inert gas atoms.... gas atoms get excited .... gas atoms then decay to give off light .... meanwhile, electrons get accelerated again..... bump into other inert gas atoms ... gas atoms get excited .... gas atoms then decay to give off light ...

Zz.
 
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