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Photoelectric effect question watch

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    Use Einsteins photoelectric effect equation to a surface of work function 2.0x10^-19 J to calculate the frequency of radiation needed to eject electrons from the surface with a max kinetic energy of 3.0x10^-19 J

    So i started off using Kemax=hf-thi but they use this equation hf=1/2mv^2max + thi we havnt even seen this equation before and it isnt in my textbook. How am i meant to know to use this and how is it derived?
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    (Original post by hazbaz)
    Use Einsteins photoelectric effect equation to a surface of work function 2.0x10^-19 J to calculate the frequency of radiation needed to eject electrons from the surface with a max kinetic energy of 3.0x10^-19 J

    So i started off using Kemax=hf-thi but they use this equation hf=1/2mv^2max + thi we havnt even seen this equation before and it isnt in my textbook. How am i meant to know to use this and how is it derived?
    K.E max is = 1/2mv^2
    They have subbed that in and then re-arranged to make hf the subject

    If you dont know where 1/2mv^2 comes from then it is just Kinetic energy..
    Energy= Work done = Force x Displacement
    Force= Mass x Acceleration
    Energy=Ma x S
    V^2=u^2 + 2as
    as= V^2-U^2/2

    We assume initial velocity = 0
    so a= V^2/2
    Energy=V^2/2 x M
    = 1/2mv^2
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    (Original post by Jian_Earle)
    K.E max is = 1/2mv^2
    They have subbed that in and then re-arranged to make hf the subject

    If you dont know where 1/2mv^2 comes from then it is just Kinetic energy..
    Energy= Work done = Force x Displacement
    Force= Mass x Acceleration
    Energy=Ma x S
    V^2=u^2 + 2as
    as= V^2-U^2/2

    We assume initial velocity = 0
    so a= V^2/2
    Energy=V^2/2 x M
    = 1/2mv^2
    Ah right yeah silly me! thanks for a min there I was thinking i had missed something really important lol cheers dude.
 
 
 
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