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Electron-photon , photon-electron

  1. Jul 14, 2013 #1
    Hi ,
    If I accelerate electrons using a electrostatic field and direct them into a plate which has the opposite charge on it for the electrons to "crash" in it , they will but after the plate there is a need for me to transport that kinetic energy that they gained when accelerated by the field to travel with a way that doesn't interact with electric field like a electron or ion would due to it's charge.
    So here is the question do electrons with sufficient kinetic energy can cause photons to be emitted from a metal plate so that they could travel further and crash into another plate and cause the photoelectric effect so that the energy I had would be transported back to electrons.

    Now I know the second one works , where I have photons of given sufficient energy and I can get electrons out when those photons hit a plate , but how does the first part works , where I have electrons that i need to make into photons so that they could transport the energy where electrons are not suited?
    I guess it should work just like the photon to electron part.

    And if sophiecentaur reads this , yes Sophie I now don't mess charge with PE anymore.Thanks for the clarification.I kinda missed that out. :)
  2. jcsd
  3. Jul 14, 2013 #2


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    Hi Crazy! Excuse me, but I'm not clear on your specific question
    "do electrons with sufficient kinetic energy can cause photons to be emitted from a metal plate so that they could travel further and crash into another plate and cause the photoelectric effect so that the energy I had would be transported back to electrons."

    Are you describing a photomultiplier tube?
    If yes, then see
    http://learn.hamamatsu.com/articles/photomultipliers.html [Broken]

    If no, please help by making your question somehow more understandable for my feeble mind to grasp. Thank you.
    Last edited by a moderator: May 6, 2017
  4. Jul 14, 2013 #3
    Hi Bobby thanks for a fast response, yeah I guess my aim was kinda unclear.
    Ok the thought is something like this.
    I have a negative electrode and a positive one , now the electrons get accelerated from the negative to the positive in a vacuum filled with an "electron gas". But in order not to get a "short circuit" between the electrodes as would normally happen , the positive electrode to which the electrodes would run is not placed inside the vacuum but insulated , instead a plate of the same negative potential is placed outside and another plate inside now as we know the outside negative plate would cause the inner plate to get polarised so that the positive charges on that plate would gather towards the negative plate outside, now to those positive inner plate charges I would like to direct those electrons.Now after they would hit the plate , I would need some kind of mechanism to get them where they started from just further do do the same ting which is to accelerate them with the electric field so that they could run into another plate like the one before.
    But when a electron with high velocity (kinetic energy) hits a plate like that the initial electron is lost but hence conservation of energy applies there must be something coming out of the plate , i assumed it could be an equivalent energy photon which could then go on to hit another plate and a electron could be born again to do the same cycle I talked about one more time.

    But the question is about the first part where the accelerated electrons hit the charged plate which is charged due to an near outside electric field.
  5. Jul 14, 2013 #4


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    It is still vey unclear what you are asking here. Are you trying to generate photons out of those primary electrons, and then the photons in turn generate secondary electrons?

    It seems as if you are more concerned about giving energy to the primary electrons? Not sure why this is a major issue since this not that difficult to accomplish (see SEM instruments).

  6. Jul 14, 2013 #5
    Well no I'm not concerned with giving energy to the primary electrons because the electric field already does that and it's his concern:)

    "It is still very unclear what you are asking here. Are you trying to generate photons out of those primary electrons, and then the photons in turn generate secondary electrons?""

    Yes exactly,I'll tell you why, the thing is imagine a round tube with vacuum and electron gas in it, now somewhere in that tube is a negative electrode (cathode) , nothing happens, then a little further is a metal plate which isn't connected with anything directly (to avoid short circuit) but has a positive plate around it outside of the tube.Which induces polarisation in the plate and hence a positive charge in the middle of the plate (because the negative has moved to the sides where the positive charge is closer from the outside) Now my electrons are feeling attraction from that positive charged region of the plate and they are accelerating from the cathode towards it.

    The thing is I have only one closed tube with electrons in it but I need atleast two of these cycles , so that when the electrons strike the plate they don't disappear. I know they can't i'm just not exactly sure what happens further , well certainly the plate get's neutralised all the time as the positive charge from the outside tries to keep it polarised but the electrons running into it are doing the opposite.
    I just need those electrons past that plate so that they could be accelerated one more time and so this goes on around the tube non stop.
    +there is a coil just after the cathode into which current is induced while the electrons go by it in a perpendicular way to the coil while on their way to the plate.I guess this has to be taken into account too as the back EMF will slow them down and the energy they'll have when crashing into the plate will be lower , so if I wanted to do the electron photon photon electron thing maybe it wouldn't be enough.
    i guess the question then is what happens to those electrons after they hit the plate at whatever speeds their in at that moment?

    Or maybe to get this whole thing working the same way , I should get rid of the inner plates , just leave the electron gas in the tube and attach metal rings or whatever metal plates at two opposite places to the tube and set those metals to positive and negative potential accordingly.
    Now according to theory the electrons should flow inside the tube as the electric field is exerting a force on them and while they flow they would induce a current in a wire wound around the tube in which they are flowing, now just for interest if this works at all just how good of a transformer would it make? :D
    Last edited: Jul 14, 2013
  7. Jul 15, 2013 #6
    Doesn't seem like this thread has got much interest but I don't blame anyone, the ideas are not that smart and probably heard , yet I have learned quite alot with these questions (specific ones) here on Pf , so thanks and any more insights on this topic much appreciated.
  8. Jul 15, 2013 #7


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    It's just really hard to follow what you're trying to do when you talk about plates inside plates that aren't grounded, those inside tubes with fields and more plates outside or something...

    We can't really answer if we can't even grasp what you're trying to do. Whatever it is you want to know, spend some time and figure out if you can use a simpler setup to find out.
  9. Jul 15, 2013 #8


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    +1 on Drakkith's comments. I looked at this thread and wanted to contribute, but I just can't visualize the setup.
  10. Jul 15, 2013 #9


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    Crazy, Ditto everything Drakkith (Edit: and DaleSpam, too) wrote above. Members here get great satisfaction by assisting a "true searcher" trying to understand how nature works. No ideas are "not smart". It's just that sometimes it is not so easy to write out the description of our ideas in plain English.

    A diagram of your proposed apparatus would help immensely.

    The term "electron gas" is often used to describe electrons in a metal, with the positive ions balancing out the negative electrons, making an approximately neutral volume, and is really a quantum-mechanical description.

    For free electrons as in a vacuum tube normally we just describe a "beam" or a "flow" leaving the cathode, focused by charged electrodes (voltage) or coils (magnetic fields), and finally impacting the anode, or screen as in a CRT. In a triode amplifier the control grid voltage modulates that flow.

    These are just a few examples of questions that could be addressed by members here:

    1. Do electrons give up all their momentum when they impact on a surface?
    2. Do the electrons forming an "electron gas" in a vacuum interact with each other?
    3. How do others build a device which accelerates electrons?
    4. When a beam of electrons passes through a coil will a current be induced?
    5. When a photon of certain energy (frequency) strikes a plate is an electron ejected (emitted)?

    If you still have questions or doubts please feel free to try again.
  11. Jul 15, 2013 #10


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    Look up Auger Effect. This has been done without needing all those gymnastics that you have been describing.

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