Coloured beam in a discharge tube

  • Context: High School 
  • Thread starter Thread starter shivanshu
  • Start date Start date
  • Tags Tags
    Beam Discharge Tube
Click For Summary

Discussion Overview

The discussion revolves around the phenomenon of colorful light observed in discharge tubes, specifically questioning why cathode rays, which are composed of electrons and do not possess color, appear as colorful rays of light when interacting with gases in the tube.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants propose that the colorful light is due to the excitation of gas within the discharge tube by the cathode rays.
  • Others mention that phosphor coatings are used in Cathode Ray Tubes (CRTs) to generate colors, suggesting a distinction between CRTs and discharge tubes.
  • A participant emphasizes that without phosphor coatings, cathode and anode rays would not be visible.
  • Another participant explains that the energy from the accelerated electron beam can be transferred to gas molecules, causing them to emit visible light upon excitation.
  • One participant reiterates the process of electrons colliding with inert gas atoms, leading to excitation and subsequent light emission.

Areas of Agreement / Disagreement

Participants generally agree that the colorful light in discharge tubes is related to the interaction between electrons and gas atoms. However, there are competing views regarding the role of phosphor coatings and the distinction between discharge tubes and CRTs, indicating that the discussion remains unresolved.

Contextual Notes

Some limitations include the potential confusion between discharge tubes and CRTs, as well as the varying levels of understanding among participants regarding the underlying physics of light emission in these contexts.

shivanshu
Messages
3
Reaction score
0
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??
 
Physics news on Phys.org
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
 

Attachments

  • 06crtmon.gif
    06crtmon.gif
    6.9 KB · Views: 1,240
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.
 
  • Like
Likes   Reactions: berkeman
berkeman said:
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
View attachment 223365
That means that we cannot see the cathode and anode rays without any phosphor coating?
 
shivanshu said:
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.
 
I still can't understand please be more explanatory...
 
shivanshu said:
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:
 
shivanshu said:
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.
 
  • Like
Likes   Reactions: DrClaude

Similar threads

High School J.J. Thomson's Coaxial Cylinders
  • · Replies 6 ·
Replies
6
Views
2K
Undergrad Why are more x-rays made from metal than glass
  • · Replies 5 ·
Replies
5
Views
2K
Graduate Interference pattern for a laser beam through an AOM
  • · Replies 4 ·
Replies
4
Views
4K
Obtain Cathode Ray Tubes Without X-rays
  • · Replies 9 ·
Replies
9
Views
2K
Undergrad Postive rays in cathode ray tube experiments?
  • · Replies 2 ·
Replies
2
Views
2K
High School Initiation and the math behind Arc Discharges
  • · Replies 8 ·
Replies
8
Views
1K
Undergrad Condenser lens retrofit for a lighting application
  • · Replies 24 ·
Replies
24
Views
3K
RF tube with photocathode, photoinjector
  • · Replies 7 ·
Replies
7
Views
2K
Undergrad Lichtenberg Figures: Positive & Negative Discharges on Plastics & Acrylic
  • · Replies 2 ·
Replies
2
Views
2K
Undergrad Why Bremsstrahlung <20keV for Tungsten?
  • · Replies 17 ·
Replies
17
Views
4K