# Q: 11.14 (a) The wavelength of light from the spectral emission line of sodium is $\dpi{100} 589\hspace{1mm}nm$. Find the kinetic energy at which an electron would have the same de Broglie wavelength.

$\\p=\frac{h}{\lambda }\\ p=\frac{6.62\times 10^{-34}}{589\times 10^{-9}}\\ p=1.12\times 10^{-27}\ kg\ m\ s^{-1}$
$\\K=\frac{p^{2}}{2m_{e}}\\ K=\frac{(1.12\times 10^{-27})^{2}}{2\times 9.1\times 10^{-31}}\\ K=6.89\times 10^{-25}\ J$