In an x-ray tube the voltage applied is 20 kV. The energy required to remove an electron from K shell is 19.9 K e V. In the x-rays emitted by the tube (h c = 12420 keÅ)

(A) Minimum wavelength will correspond to maximum energy i.e.,from   $\lambda$ to k.
 $\begin{array}{l}\Delta E=19.9KeV\\ \therefore {\lambda }_{\min }=\frac{1.24\times {10}^4}{19.9\times {10}^3}\stackrel{\circ }{\text{A}}=0.62\stackrel{\circ }{\text{A}}=62pm.\end{array}$
(B) (B) Energy of the characteristic x–rays will be less than corresponding to  $\alpha$ to K– shell, hence than 19.9 keV.