# a beam of helium atoms moves with a velocity of 20000 m/s. Find the wavelength of particles constituting with the beam

Please find below the solution to the asked query:

According to de-Broglie relation: $\lambda =\frac{h}{P}=\frac{h}{mv}$

As 1 mol or 4 g of He contains 6.022 x 10

^{23}atoms, then mass of single He atom = (4 / 6.022 x 10

^{23}) = 6.64 x 10

^{-24}g

Hence, the wavelength = $\lambda =\frac{h}{mv}=\frac{6.626\times {10}^{-34}Kg{m}^{2}{s}^{-1}}{6.64\times {10}^{-27}Kg\times 20000m{s}^{-1}}=4.99\times {10}^{-12}m\phantom{\rule{0ex}{0ex}}\lambda =\mathbf{499}\mathbf{}\mathit{p}\mathit{m}$

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