$lambda = "0.388 nm"$ .
Well, since an electron is a particle with mass, it can be described by the de Broglie relation:
$lambda = h/(mv)$ where:
$h = 6.626 xx 10^(-34) "J"cdot"s"$ is . Remember that$"1 J" = ("1 kg"cdot"m"^2)/"s"$ .$m_e = 9.109 xx 10^(-31) "kg"$ is the rest mass of an electron.$v$ is its speed. We don't need to know that per se.
And since it is also moving with a certain speed, it will have a kinetic energy of:
$K = 1/2 mv^2 = p^2/(2m)$ where:
$p = mv$ is the linear momentum of the particle.$m$ is the mass of the particle.$v$ is the speed of the particle.
And so, we can get the forward momentum in terms of the kinetic energy:
$p = sqrt(2mK) = mv$
Lastly, note that in
Therefore, the de Broglie wavelength of the electron is:
$color(blue)(lambda) = h/sqrt(2m_eK_e)$
$= (6.626 xx 10^(-34) cancel"kg"cdot"m"^cancel(2)"/"cancel"s")/sqrt(2 cdot 9.109 xx 10^(-31) cancel"kg" cdot 10 cancel"eV" xx (1.602 xx 10^(-19) cancel"kg"cdotcancel("m"^2)"/"cancel("s"^2))/(cancel"1 eV"))$
$= 3.88 xx 10^(-10) "m"$
$=$ $color(blue)("0.388 nm")$
And so, this is on the order of an X-ray photoelectron.