Question

To decrease the cut-off wavelength of continuous $X$ -ray by $25\%$ , the potential difference across the $X$ -ray tube

• A. must be increased by $\frac{100}{3}\%$
• B. must be decreased by $20\%$
• C. must be increased by $25\%$
• D. must be decreased by $25\%$

Answer 1

Answer: (A)

$\lambda =\frac{h c}{e V},\frac{\lambda _{1}}{\lambda _{2}}=\frac{V_{2}}{V_{1}},\lambda _{2}=\frac{3}{4}\lambda _{1}$
$V_{2}=\frac{4}{3}V_{1}\left(w h i c h \, i s \, e q u a l \, t o \, \frac{100}{3} \% \, i n c r e a s e\right)$