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    Hi everyone,

    I'm revising for a QM exam but some of this question is A-level-ish

    I'm simpley not getting the answers provided, which are after each question in brackets

    A1: Caluclate the wavelegnth of the following:
    a) a 10eV photon (3.1E^{-9}m)
    b) an electron with a kinetic energy of 10eV (3.9E^{-10}m)
    c) a thermal neutron of average kinetic energy in a neutron gas of temperature 300K (6.2E^{(-9}m)
    d) a tennis ball with mass of 57g travelling at 50m/s (2.3E^{-34})

    Does anyone actually get these answers?
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    I make (a) 1.2 x 10^-7 m; I can't see where their answer comes from.

    I agree with (b). First work out the velocity of the electron, then use the de Broigle equation (ignoring relativistic effects).

    I don't have the knowledge to comment on (c).

    I agree with (d); it's a straightforward application of the de Broigle equation.
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    for c) you can find the average translational kinetic energy of the neutron, given by (3/2)kT where k is the boltzmann and T is temperature in kelvin. plug that into KE=(p^2)/(2m) to find momentum of the neutron and voila
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    I'm not 100% sure if I did correctly, but I agree with C.

    Use kinetic theory of gases - \left< E_k \right> =\tfrac{3}{2}k_{\text{B}}T.

    Express mean momentum in terms of mean kinetic energy. Then use the Broglie relation of wavelength and momentum.
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    I have to disagree that k is Stefan-Boltzmann constant. The Stefan-Boltzmann constant is used in Stefan-Boltzmann law: P/A=\sigma T^4.
    The k in kinetic theory of gases is just Boltzmann constant.
 
 
 
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