The wavelength
of 20 eV electrons is about 2.7 Angstroms (2.7 x 10^{-10}
m)

**Rationale**

It is best to simplify the equation by substituting for all the
known variables except the electron voltage, V , and simultaneously
multiplying by 10^{10} to accommodate the change in units
from metres to Angstroms : this gives

Wavelength, λ ~ ( 150 / V )^{1/2}
Angstroms

Substituting V = 20 gives a wavelength of around 2.7 Angstroms .