Question

Iron emits K_α X-ray of energy 6.4 keV. Calculate the times taken by an iron K_α photon to cross through a distance of 3 km.

Answer 1

Given:
Energy of the X-ray, E = 6.4 keV
Distance travelled by the photon, d = 3 km = 3 $\times$ 10³ m
Time taken by the photon to cross the distance of 3 km is given by
$$\begin{gathered} t=\frac{\mathrm{Distance}}{\mathrm{Speed}}=\frac{3\times {10}^3}{3\times {10}^8} \\ t={10}^{-5}\mathrm{s}=10\times {10}^{-6}\mathrm{s} \\ t=10\mathrm{\mu s} \end{gathered}$$

Both the K_α photon and X-ray will take the same time, that is, 10 $\mathrm{\mu s}$, to cross the distance of 3 km.