If the lattice constant of a crystal is $3 \times 10^{-8} \, cm$ and the glancing angle for the first-order diffraction of $X$-rays is $30^{\circ}$,then the value of $\lambda$ will be ..... $\times 10^{-8} \, cm$.

The minimum wavelength of $X$-rays produced by electrons accelerated by a potential difference of $V$ volts is equal to:

The wavelength of the $L_\alpha$ $X$-ray line of $Pt^{78}$ is $1.32 \, \mathring A$. The wavelength of the $L_\alpha$ line in the $X$-ray spectrum of another unknown element is $4.17 \, \mathring A$. If the screening constant for the $L_\alpha$ line is $7.4$,then the atomic number of the unknown element is:

$A$ hydrogen atom does not emit $X$-rays because

An electron beam strikes a target at an accelerating potential of $50 \,kV$. Which of the following frequencies of $X$-rays will not be obtained?

The wavelength $\lambda$ of the ${K_{\alpha}}$ line of characteristic $X$-ray spectra varies with atomic number $Z$ approximately as: