Hard X -rays for the study of fractures in bones should have a...

From conservation of energy the kinetic energy of electron equals the maximum photon energy (we neglect the work function $\phi$ because it is normally so small compared to $e V_0$ ). $\therefore \quad e V_0=h v_{\max }$ or $e V_0=\frac{h c}{\lambda_{\min }} \therefore \quad V_0=\frac{h c}{e \lambda_{\min }} or$$\begin{aligned} V_0 & =\frac{12400 \times 10^{-10}}{10^{-11}} \\ & =124 \mathrm{kV}\end{aligned}$$$Hence, accelerating voltage for electrons in$X$-ray machine should be less than 124 kV .