Question

An X-ray tube is operating at 84 kV mA. Only 1% of the electric power supplied is converted into X-rays. If target has a mass of 300 gm and specific heat of 0.04 cal/gm/ ${}^{o}C$. Then choose the correct statements from the options below. (use 1 cal = 4.2 J & hc = 12400 ev - ${}^{o}A$) Assume entire thermal energy is absorbed by the target.

• A. cut-off wavelength is approximately 0.15 ${}^{o}A$
• B. cut-off wavelength is approximately 6.8 ${}^{o}A$
• C. average rate of temperature rise of target (assuming no heat loss) is 16.5 ${}^{o}C/sec$
• D. average rate of temperature rise of target (assuming no heat loss) is ${1.7}^{o}C/sec$.

Answer 1

Answer: (A), (C)

The correct options are
A

cut-off wavelength is approximately 0.15 ${}^{o}A$

C

average rate of temperature rise of target (assuming no heat loss) is 16.5 ${}^{o}C/sec$

${\lambda }_{\text{cut off}}=\frac{12400}{84000}=0.15A^{\circ }99\%ofpower=84000\times 10\times {10}^{-3}\times 0.99=300\times 0.04\times 4.2\frac{dT}{dt}\Rightarrow \frac{dT}{dt}={16.5}^{o}C/sec.$