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Photoelectric Effect & Energy Levels - Help in understanding Watch

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    I'm self studying so looking for a little clarification in my studies, any help is appreciated.


    Firstly - I've looked at the photoelectric effect and learnt about the threshold frequency for an electron to be released and if this is not reached nothing happens but then I've turned over the page (AQA book) and it now states about energy levels and how electrons can move up energy levels before finally becoming free electrons if there is enough energy. So I'm a little confused, my understanding is that the photoelectric effect is talking about the required photon frequency and an overall total energy (work function) to free an electron whereas the energy levels dives a bit deeper into this showing that electrons can receive more energy without becoming free electrons...

    Secondly - Regarding florescent tubes, high voltage in mercury vapour is used and then the UV light is converted with a phosphorus coating to produce visible light. Why can't they just use high voltage in phosphorus to excite the electrons and then as they drop energy levels produce visible light. Obviously there's a reason for the two stages but I can't put my finger on it...
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    (Original post by VulcanMonk)
    I'm self studying so looking for a little clarification in my studies, any help is appreciated.


    Firstly - I've looked at the photoelectric effect and learnt about the threshold frequency for an electron to be released and if this is not reached nothing happens but then I've turned over the page (AQA book) and it now states about energy levels and how electrons can move up energy levels before finally becoming free electrons if there is enough energy. So I'm a little confused, my understanding is that the photoelectric effect is talking about the required photon frequency and an overall total energy (work function) to free an electron whereas the energy levels dives a bit deeper into this showing that electrons can receive more energy without becoming free electrons...

    Secondly - Regarding florescent tubes, high voltage in mercury vapour is used and then the UV light is converted with a phosphorus coating to produce visible light. Why can't they just use high voltage in phosphorus to excite the electrons and then as they drop energy levels produce visible light. Obviously there's a reason for the two stages but I can't put my finger on it...
    you seem to have it correct, the photolectric effect looks at the amount of energy needed to free an electron from it's atom, but electrons inside an atom exist at discrete energy levels and can jump up to a higher energy level or down to a lower energy level by absorbing or emitting a photon, usually textbooks would be looking at the Bohr model of H atoms here.

    electroluminescence is used for illuminating some car dashboards, watch dials etc. I guess it's difficult/expensive to get it working as a powerful lightsource like a flourescent tube but tbh I don't know really what those problems are.
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    Thanks, sometimes I just need someone to say yes you're doing it right! I shall have a look into electroluminescence, thanks for pointing me the right way.
 
 
 
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