\(\frac{{{p^2}}}{{2me}} = eV\,\,\,\)
\(P = \sqrt {2me\,\,eV} = \sqrt {2 \times 2.1 \times {{10}^{ - 31}} \times 1.6 \times {{10}^{ - 19}} \times 50000} \)
\( = \,\sqrt {14.56 \times {{10}^{ - 50}} \times {{10}^4}} = 12.06 \times {10^{ - 23}}kg\,m/\sec \)
\(\lambda = \frac{h}{p} = \frac{{6.6 \times {{10}^{ - 34}}}}{{12.06 \times {{10}^{ - 23}}}}m = \frac{{6.6}}{{12.06}} \times {10^{ - 11}}m = 0.055\,{\text{Å}}\)
$\left(\mathrm{m}_{\mathrm{e}}=9 \times 10^{-31}\;\mathrm{kg}\right)$
$\left({h}=6.63 \times 10^{-34}\, {J} \cdots\right.$, $\left.{c}=3 \times 10^{8} \,{ms}^{-1}\right)$