Question

The figure shows the intensity-wavelength relations of X-rays coming from two different Coolidge tubes. The solid curve represents the relation for the tube A in which the potential difference between the target and the filament is VA and the atomic number of the target material is ZA. These quantities are VB and ZB for the other tube. Then,
(a) VA > VB, ZA > ZB
(b) VA > VB, ZA < ZB
(c) VA < VB, ZA > ZB
(d) VA > VB, ZA < ZB
Figure

Answer 1

The correct answer is (b) VA > VB, ZA < ZB

EXPLANATION:

• From the figure, it is evident that more than the tube B’s x-ray, the tube A’s x-ray has less cut-off wavelength.  

• Therefore, λA < λB  

• When Moseley’s Law is used,

• ZB > ZA

• λ ∝ 1V, where the applied voltage is denoted by V in the X-ray tube.

• Therefore, VB < VB

• The wavelength at which the optical fibre becomes single mode is called the cut-off wavelength.