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"de broglie" question watch

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    hi,

    I need help with the following questions:

    An electron has kinetic energy 3.00 eV. Find its wavelength?

    i thought i would use 1/2mv^2 = 3 to find v which = 2.57x10^15.

    then using that, put it into h/mv so it = 2.83x10^-19. But this answer is wrong!:confused: i got no idea how to do this now...please help!!
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    Remember that the equations work in joules. You need to convert the 3eV into joules before you subsitute it into ke=0.5mv^2 to get the right answer.
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    oh so divide by 1.6x10^-19??
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    No 1 eV=1.6x10^-19 Joules. So 3 eV would be 3 times that wouldn't it? ^^
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    does m = rest mass of electron(9.11*10-31)
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    At AS, yes you would have to use that.
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    (Original post by malolis)
    No 1 eV=1.6x10^-19 Joules. So 3 eV would be 3 times that wouldn't it? ^^

    ye sorry!



    would the answer be 7.09x10^-10
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    I get 1x10^-9 but I could be wrong. Check the answer - you said you have it!
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    sounds about right, i normally get something to the ^-10, when working out the de broglie wavelength
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    thank you very much
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    (Original post by malolis)
    I get 1x10^-9 but I could be wrong. Check the answer - you said you have it!
    it was 7.09*10^-10 thanks for your help!!
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    (Original post by Alevelstudent123)
    it was 7.09*10^-10 thanks for your help!!
    Yes thats right, I forgot to multiply by 2 when working out the velocity from ke=0.5mv^2 ^^

    I fail...
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    i dont suppose you no how to do this do you?

    "A photon has energy 2.00 eV. Find its wavelength."

    cos i got no idea!
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    if you convert the energy into joules, the use the equation p=E/c, to find the momentum, then use h/p=de broglie wavelength, i think that'll give you the correct answer

    (Original post by Alevelstudent123)
    i dont suppose you no how to do this do you?

    "A photon has energy 2.00 eV. Find its wavelength."

    cos i got no idea!
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    (Original post by Alevelstudent123)
    i dont suppose you no how to do this do you?

    "A photon has energy 2.00 eV. Find its wavelength."

    cos i got no idea!
    You could just use E=hf and c= fλ to get E= hc/λ i.e. λ = hc/E
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    thanks a lot you really are a great help!
 
 
 
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