MadSci Network: Physics

Re: Why is the Cathode Ray tube cyindrical?

Date: Thu Jul 5 10:45:10 2001
Posted By: Nauzad Tantra, Undergraduate, Production/ Industrial engg., D J Sanghvi college of engg.
Area of science: Physics
ID: 994056532.Ph

Hi Girish,
The question asked is very interesting, and very simple to answer too, 
with a little thinking.

Your first question is why cathode ray tubes are cylindrical. Rather than 
giving a direct answer, think what would happen if the cathode ray tube 
were square or triangular or maybe any other shape you may wish ( 
hexagonal, rectangular...). 
The next stage is to think whether this will affect the functioning of the 
tube. The answer obviously is NO. Why? Because the rays being emmited out 
of the tube are electrons which can pass through any media and do not need 
a certain shape of a container to pass through. Imagine the electrons to 
be like water passing through a pipe. The water will pass irrespective of 
the shape of the cross section of the pipe. However we hardly see pipes 
which are non-cylindrical. Why? Only because its easier to manufacture a 
pipe which is cylindrical.

The same can be said for a glass tube. Round cross sections are easier to 
manufacture with glass by traditional blowing. Thats why cups and glasses, 
electric bulbs and flourescent tubes and most other glass items that you 
see around you are round.

Your next question asks if the cathode plate is tilted in the Cathode ray 
experiment, would the cathode rays still come out normal to the plate. 
Use the same example of water given above to get the answer to this 
question too. If a dam had an inclined sluice gate would the water come 
out perpendicular to it? NO. The same can be said for cathode tubes, which 
will not affect the direction of flow of electrons by tilting the plate. 
(PS: If this were true, imagine what would happen if the cathode were 
tilted 90'. Then the anode would become redundant :)

Hope this answers your doubts. Do mail me if you want further 

Best of luck

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