The transition from the state $n = 4$ to $n = 3$ in a hydrogen-like atom results in ultraviolet radiation. Infrared radiation will be obtained in the transition

What was the thickness of the gold foil kept in the Geiger-Marsden scattering experiment?

The figure represents the observed intensity of $X-$rays emitted by an $X-$ray tube, as a function of wavelength. The sharp peaks $A$ and $B$ denote

Hydrogen $(H)$, deuterium $(D)$, singly ionized helium $(H{e^ + })$ and doubly ionized lithium $(Li)$ all have one electron around the nucleus. Consider $n =2$ to $n = 1 $ transition. The wavelengths of emitted radiations are ${\lambda _1},\;{\lambda _2},\;{\lambda _3}$ and ${\lambda _4}$ respectively. Then approximately

$X$-rays incident on a material