The wavelength of the most energetic $X$-rays emitted when a metal target is bombarded by $40 \ keV$ electrons is approximately .............. $\mathring{A}$.

$X$-rays of wavelength $22 \, pm$ are scattered from a carbon target at an angle of $85^{\circ}$ to the incident beam. The Compton shift for $X$-rays is ......... $pm$.

If the operating voltage of an $X$-ray tube is $50 \, kV$,then the velocity of the $X$-rays is . . . . .

If $X$-rays pass through a strong magnetic field,the $X$-rays . . . . . .

When the atomic number of the first target is $Z_1 = 64$ and the atomic number of the second target is $Z_2 = 80$,the approximate ratio of the wavelengths of the $K_{\alpha,1}$ and $K_{\alpha,2}$ radiations is .......

$A$ charged gold leaf electroscope has its leaves apart by a certain amount with enclosed air. When the electroscope is subjected to $X$-rays,then the leaves