Q.

A metal target with atomic number Z = 46 is bombarded with a high energy electron beam. The emission of X-rays from the target is analyzed. The ratio r of the wavelengths of the Kα-line and the cut-off is found to be r=2. If the same electron beam bombards another metal target with Z = 41, the value of r will be               [2024]

1 2.53  
2 1.27  
3 2.24  
4 1.58  

Ans.

(1)

The ratio of the wavelengths of the Kα-line and the cut-off i.e.

λKαλ0(=r)∝1(Z-1)2

∴  r2r1=(Z1-1)2(Z2-1)2=(46-1)2(41-1)2=452402

or,  r2=1.265×r1=1.265×2=2.53