Anode accelerators in CRTs (1 Viewer)

[Giant Lobster]

About CRTs, the books briefly mention electrons are accelerated by anode plates outside of the evacuated chamber. How does this work? I know the plates are +ve and thus would pull electrons but once they reach the closest point the force will be pulling them back; slowing them down... I don't get that.

 

[raging]

i guess exam wise we just have to mention that anodes are used in CRTs to accelerate the electrons produced by thermionic emission and they are later deflected by two pairs of capacitor plates

i doubt questions like this woudl worth more than two marks

 

[jims]

between the thermionic emission thing and the anode theres an electric field, so the electrons are affected by it (ie attracted towards the anode)
but theres no cathodic plate behind that anode so no electric field exists there, ergo its not attracted back. i think thats how it works....

 

[Giant Lobster]

hmmm nah what im asking is since electrons are attracted to anodes, and they use them as accelerators and not the actual target, wont the electrons be pulled backwards once it passes the anode accelerators?

 

[inasero]

hmmm not unless the kinetic force exceeds that of the electrical attractive force....

 

[Giant Lobster]

yeah of course.. but wouldnt that defeat the purpose? cos the anode gives a certain pull in the correct direction, then negates its own contributions after the electron has past the point. so the net effect is that the electron wasnt helped at all by the anode
well ideally, the anode wont even let the electron pass and itll just accumulate near the anodes... i still dun get this.

 

[inasero]

hmm i getcha now...good question

also what i dont understand is u know how the crookes bent tube demonstrates that cathode rays travel in a straight line right? but if the stream of electrons hits the glass on the opposite side then how do they reach the anode to complete the circuit?

it doesnt make sense

 

[Giant Lobster]

yeh im full lost when it comes to cathodes.
im naturally inclined to think gases are insulators, but apparently that isnt the case.

 

[punk0rz]

the terms 'insulators' and 'conductors' are decieving, as a so called 'insulator' will become a 'conductor' given a high enough potential difference. instead, classing something as a 'good' or a 'poor' conductor makes more sense to me. gases are generally 'poor' conductors unless at low pressure and high potential difference - ie there are less gas particles obstructing the path of electrons, hence when a large potential difference is applied they are 'conducted' mainly through empty space... this is how it seems to make sense to me anyhow.. as for crookes bent tube, we haven't covered that in class - the maltese cross experiment seems to prove the same phenomena and in a much more easily understood fashion. im assuming crookes bent tube is a cathode ray tube with a bend in it somewhere (yes im a genius) - where is the bend and how sharp is it? im assuming it would have to be relatively obtuse to allow at least some electrons reach the cathode, with a relatively small percentile striking the edge of the bend on transit...