momentum

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do gamma rays carry momentum? i thought they don't because they don't have mass so mv=0 but my frend says even tho they don't have mass they still carry momentum. how does this make sense? please help.

  • momentum -

    Photons in general carry momentum so any electromagnetic wave has momentum associated with it despite its lick of rest mass in the classical sense. If a photon hits something, it moves it.

    E = energy of photon = m c^2 = h f where c is velocity of light and h is plank constant and f is the frequency
    Of course we know classical rest mass m is zero but that does not prove there is no energy, m c^2 at the velocity of light.
    then m c = momentum p
    but m c = E/c
    so p = E/c
    but E = h f
    so
    momentum p = h f /c
    but f/c = 1/Tc = 1/Lambda
    where T is period and Lambda is wavelength
    so
    p = h/Lambda

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