The $K, L$ and $M$ energy levels of platinum lie roughly at $78, 12$ and $3 \ keV$ respectively. The ratio of the wavelength of the $K_{\alpha}$ line to that of the $K_{\beta}$ line in the $X$-ray spectrum is:

Hydrogen atom does not emit $X$-rays because

The minimum wavelength of $X$-rays produced by $20 \ kV$ electrons is nearly (in $Å$)

The graph between the square root of the frequency of a characteristic line in the $X$-ray spectrum and the atomic number of the target is:

$A$ potential difference of $42,000 \ V$ is used in an $X-ray$ tube to accelerate electrons. The maximum frequency of the $X-radiations$ produced is ($1 \ eV = 1.6 \times 10^{-19} \ J$ and $h = 6.63 \times 10^{-34} \ J \cdot s$).

$A$ metal target with atomic number $Z=46$ is bombarded with a high-energy electron beam. The emission of $X$-rays from the target is analyzed. The ratio $r$ of the wavelengths of the $K_\alpha$-line and the cut-off wavelength is found to be $r=2$. If the same electron beam bombards another metal target with $Z=41$,the value of $r$ will be