Question

The cut off wavelength of continuous X-ray from two coolidge tubes operating at 30 kV but using different target materials (molybdenum Z= 42 and tungsten Z = 74) are

• A. 1Å, 3Å
• B. 0.3 Å, 0.2 Å
• C. 0.414 Å, 0.8 Å
• D. 0.414 Å, 0.414 Å

Answer 1

Answer: (D)

0.414 Å, 0.414 Å

Answer 2

Cut off wavelength of continuous X-rays depends solely on the voltage applied and does not depend on the material of the target. Hence the two tubes will have the same cut off wavelength.

$Ve = h\nu = \frac{hc}{\lambda}$ or

$\lambda = \frac{hc}{Ve} = \frac{6.627 \times 10^{- 34} \times 3 \times 10^{8}}{30 \times 10^{3} \times 1.6 \times 10^{- 19}}m = 414 \times 10^{= 10}m = 0.414Å.$