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Helical Electron Path





Dennise
I did an interesting senior collage project around 1969 that was quite cool and satisfying.

The project consisted of a clear glass tube about 8 inches in diameter and six feet long. This tube was fitted with an electron producing filament at one end and an electron collecting plate at the other end, with a variable DC electric voltage applied across these ends. Two addition components completed the experimental setup.

The air in the glass tube was evacuated and replaced with an inert gas (argon, helium and neon were the gas choices as I recall). Finally, the tube was surrounded by a large copper coil which produced a variable magnetic field.

The object of the experiment was to combine these variables:

    electron source strength
    end to end electric field strength
    radial magnetic field strength
    inert gas type and pressure
;

in such a way as to produce a visible light stream from electron-gas atom collisions, under the influence of both electric and magnetic fields. The cool part, and the experiment's end objective, was that when all the variables were just right, the very visible blue electron stream followed a nice helical path from one end of the tube to the other.

After understanding the electron motion equations together with mastering the practical parts of the experiment, wah la ...... success and a nice pat on the back from my professor.

Has anyone ever heard about or seen such an experiment? I have long lost my report on the experiment and would sure like to see or read about someone else who did/does this. I have been unable to find any record of this experiment in My Alma Matter's arcives (Penn State).
coolclay
Wow, that is quite fascinating. So I looked up some more info, I think you are referring to a Crookes tube http://en.wikipedia.org/wiki/Crookes_tube.
Dennise
coolclay wrote:
Wow, that is quite fascinating. So I looked up some more info, I think you are referring to a Crookes tube http://en.wikipedia.org/wiki/Crookes_tube.


Well yes, Crooks Tubes were used to demonstrate the linear path of electrons in an air evacuated tube - and someone did demonstrate the magnetic deflection of such a path. Indeed this was the basis of what I did.

The difference though, was to get the electric and magnetic fields balanced just right so that the electrons followed a visible helical path from cathode to anode. When balanced correctly, I was able to play with the electric field and make the electron helix look like a helical spring inside that tube and was able pull the 'spring' back and forth.

I'd still like to see or read about a demonstration that is/was like my senior project in college.
365427417
Learning under
Dennise
365427417 wrote:
Learning under


????
LxGoodies
Dennise wrote:
coolclay wrote:
Wow, that is quite fascinating. So I looked up some more info, I think you are referring to a Crookes tube http://en.wikipedia.org/wiki/Crookes_tube.


Well yes, Crooks Tubes were used to demonstrate the linear path of electrons in an air evacuated tube - and someone did demonstrate the magnetic deflection of such a path. Indeed this was the basis of what I did.

sounds like CRT (Cathode Ray Tube) technology..

Quote:
The difference though, was to get the electric and magnetic fields balanced just right so that the electrons followed a visible helical path from cathode to anode.

So you'd like to focus so electrons get visible. This will only require a sufficient electron density and magnetic field. Electrons always move in a helical path, in a uniform magnetic field. The intensity of the magnetic field will decide the radius and spring density, dependent on the starting velocity of the electron, which is your balanced electric field... that is the device that accellerates your electron before entering the magnetic field.

http://www.physicsforums.com/archive/index.php/t-79340.html
http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=2400.0

Quote:
When balanced correctly, I was able to play with the electric field and make the electron helix look like a helical spring inside that tube and was able pull the 'spring' back and forth.

Aha that would happen on a step response in the electric field ! Interesting dynamics..

Quote:
I'd still like to see or read about a demonstration that is/was like my senior project in college.

I share your nostalgia.. It would be nice to program a TI-59 again, be a student, 19. Unfortunately I'm age 50, still kicking.. but it would be difficult to re-envision all these beautiful inventions I did and BUT never created.. because I'm too lazy

greetzz

Very Happy Very Happy Goodies (collegue former physics student)
Dennise
Quote:
So you'd like to focus so electrons get visible.


Well not exactly. As the electrons in the focused beam collided with the gas atoms, those atoms' electrons were exited into higher energy states. Then when the electrons fell back into lower energy states, photons were emitted in the visible light spectrum.

I'm sure that's what you meant, yes?
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