Recently it has become possible to alter the velocity of gaseous atoms with radi

Question

Recently it has become possible to alter the velocity of gaseous atoms with radiation pressure from laser beams. In one experiment an atomic beam of sodium atoms was brought almost to a standstill by shining lasers from six directions tuned to the D-line of Na. In this "optical molasses" the atoms move sluggishly about with an average velocity of 40 cm?s?1.

Find the de Broglie wavelength of these atoms. (Using this method, a so-called Bose-Einstein condensate has been made, an ultracold cluster of atoms that behaves like one giant atom.)

Explanation / Answer

Each mole sodium atoms weigh 23 grams.
so one atome weighs 23/(6.023*10^23) = 3.833*10^(-23) grams.

de broglie's wavelength = h/p
where h= planck's constant,
p=momentum.
hence wavelength = [6.625*10^(-34)] / [{3.833*10^(-23)}*40*10^(-2)] = 6.651*10^(-13) metres = 0.651 pico Meters.

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