 Solution

Nonrelativistic acceleration from rest gives $p=\sqrt{2m_{e}eV}$ and $\lambda =h/p$. The observed deflection is the angle between incident and diffracted beams, $2\theta =22^{\circ }$, so Bragg's law at first order givesHere $\lambda \simeq 0.100\mathrm{nm}$. The numerical evaluation uses the externally documented CODATA 2014 values $h=6.626070040\times 10^{-34}\mathrm{J}\mathrm{s}$, $m_e=9.10938356\times 10^{-31}\mathrm{kg}$ and $e=1.6021766208\times 10^{-19}\mathrm{C}$; it does not assert which rounded constants were in the exam's handbook. Relativistic corrections at this voltage are negligible at the precision of the angle.^[ref]