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

Characteristic $X$-rays are not obtained in the spectrum of a hydrogen atom because,

Two elements $A$ and $B$ with atomic numbers $Z_{A}$ and $Z_{B}$ are used to produce characteristic $X$-rays with frequencies $v_{A}$ and $v_{B}$ respectively. If $Z_{A}: Z_{B} = 1: 2$, then $v_{A}: v_{B}$ will be

For the production of $X$-rays of wavelength $0.1 \mathring{A}$,the minimum potential difference required will be.....$kV$.

The wavelength of the series limit of the Lyman series in the hydrogen spectrum is $911 \ \mathring{A}$. Calculate the atomic number of the element that emits characteristic $X$-rays with a minimum wavelength of $0.7 \ \mathring{A}$.

When an $X$-ray of wavelength $0.5 \, \mathring{A}$ passes through a metal foil of thickness $3.5 \, mm$,its intensity is reduced to one-fourth of its initial value. The absorption coefficient of the metal is ..... $mm^{-1}$.