Explanation

(a) From conservation of energy the electron kinetic energy equals the maximum photon energy (we neglect the work function $\phi$ because it is normally so small compared to $eV_{0}$).
$eV_{0} = hv$$_{max}$
or $eV_{0} = \frac{hc}{{\lambda\ }_{\min}}$
$\therefore\ \ \ \ \ \ \ \ \ \ {\ V}_{0} = \frac{hc}{{e\lambda\ }_{\min}}$
or $V_{0} = \ \frac{12400 \times 10^{- 10}}{10^{- 11}}$ =124 kv
Hence, accelerating voltage for electrons in X–ray machine should be less than 124 kv.