What must be the velocity, in meters per second, of a beam of electrons if they are to display a de Broglie wa?

What must be the velocity, in meters per second, of a beam of electrons if they are to display a de Broglie wavelength of 21.3 μm?

the de Broglie wavelength, L, is given by

L = h/mv

h=planck's cst = 66.2x10^(-34)Js
m=9.1x10^(-31)kg
v=velocity
L=21.3 microns = 2.13x10^(-5)m

solve for v:

v=h/(m L)

now substitute values and solve for v

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