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)

$\lambda =\frac{hc}{eV},\frac{{\lambda }_1}{{\lambda }_2}=\frac{V_2}{V_1},{\lambda }_2=\frac{3}{4}{\lambda }_1$
$V_2=\frac{4}{3}{V}_1\left(whichisequalto\frac{100}{3}\%increase\right)$