Calculate the wavelength for the emission of a photon having a wave number of $11516 \ cm^{-1}$. (in $nm$)

In the hydrogen spectrum,the various lines of the Lyman series lie in the $.......$ region.

Identify the region of the electromagnetic spectrum for the spectral lines when electron transition takes place from higher energy levels to $n=3, 4, 5$ in the atomic spectrum of hydrogen.

Which of the following statements is correct about the photoelectric effect?
$1$. The number of electrons ejected from a metal surface is inversely proportional to the intensity of light.
$2$. Below the threshold frequency,the photoelectric effect can be observed.
$3$. At a frequency higher than the threshold frequency,the ejected electrons have a certain kinetic energy.
$4$. At a frequency higher than the threshold frequency,the electron is still on the metal surface.

Explain the production,characteristics,and uses of $X$-rays.

Describe the electromagnetic spectrum.