How does an electron gun shoot a stream of electrons?


by Cyberice
Tags: electron, electrons, shoot, stream
Cyberice
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#1
Aug8-03, 10:15 PM
P: 50
Electricity is the movement of electrons from attom to atom but how are streams of electrons shot through the air to hit a phosphor screen in a TV or monitor by an electron gun? I have heard of electrical arc's but when those are preformed there are usually sparks going every where so I know it doesn't use an arch to reach the screen or to remove the elctrons from the atom.

I just don't see how an electron can be removed from it's atom to fly throught the air and make it to the screen. In electricity the same electrons are "recycled" over and over again throught the circuit by using the electron present in the conductor. But how the the atoms get their electrons back after having them shot off by an electron gun? How does the electron gun take away an atoms electron with out replacing it with another one immetiately? How can you recycle the electrons once they hit the screen back into the atoms used for the electron gun? And where do the electrons go after they hit the phosphor to light it up? They obvioulsy don't build up, so do they just fall off? And to top off that pile of questions: Is the inside of a CRT a vaccum? Because if it isn't then how do the elements (gasses and dust) not interfere with the electons to prevent them from hitting the screen and using them for themselves?

I would LOVE to hear a good explanation to this.
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radagast
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#2
Aug8-03, 10:33 PM
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Atoms loose and gain electrons all the time. When they have an unbalanced number they are called ions. This can occur through chemical means, electrical means, or just plain getting enough energy into an atom, such that the electrons are raised to an energy level allowing them to leave.

For example, in the circuit example you used - take a capacitor. Once the capacitor is charged, then part of the capacitor has too many electrons, thus a negative charge, the other a positive charge. They aren't balanced (or recycled as you put it) until the capcitor is discharged. Clouds can form a half of a giant capacity, which discharges in the form of lightning.

In the case of an electron gun, the guns element (similar to the filiment in a light bulb, is heated and kept at a high negative voltage. A screen not too far from the filiment has a high, but opposite charge, such that when the filiment is heated and the electrons have enough energy to escape they fly toward the screen. Their kinetic energy is enough to keep most of them traveling toward the picture screen. In this case, the vacuum of the picture tube is substituted for a wire. The net negative charge of the filiment is reduced by the leaving electrons, which travel to the screen, reducing it's net positive charge. Since circuits supply both the positive charge of the screen and the negative charge of the filiment, there is a flow of current from the filiment to the screen via the vacuum of the tube.

I'm sure I got many of the details incorrect, but the basics of how it works is enough to give you the idea.

Electrically charged particles (protons) form the solar winds, which cause the Auroras.
Cyberice
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#3
Aug8-03, 10:45 PM
P: 50
Thanks for the info. I actually learned something. [:)]

radagast
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#4
Aug9-03, 10:23 PM
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How does an electron gun shoot a stream of electrons?


I live to serve. [;)]
ShadowKnight
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#5
Aug28-03, 12:42 PM
P: 55
I know this is an older post post but thought you may be interested in more. To answer your questions (the best I can)
Yes, a CRT used in a TV or computer monitor is a vacuum.
The electrons from the "gun" are replenished by the AC power coming into the TV. This brings a constant source of new electrons.
Where does the electron go? You are right, it doesn't build up on the screen. When an electron hits the phosphor of the screen it becomes light energy. The light energy leaves the screen as light, not as an electron directly. This is extremely simplified, but gets the point across.
You should read here if you want to know more.
http://entertainment.howstuffworks.com/tv.htm
radagast
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#6
Sep9-03, 11:41 AM
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P: 460
The electrons may trigger light emission, but they do not 'become light energy' as in electron hits the phosphor of the screen it becomes light energy.

The gun and the screen are just two points along a circuit. The AC is converted to high voltage DC, the electrons travel fromt the DC source, into the gun, are shot at the screen, collected at the screen, and travel back into the DC source.


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