$X$-rays are produced due to

The work functions of $Ag, Mg, K$ and $Na$ respectively in $eV$ are $4.3, 3.7, 2.25, 2.30$. When an electromagnetic radiation of wavelength of $300 \ nm$ is allowed to fall on these metal surfaces,the number of metals from which the electrons are ejected is $(eV = 1.6022 \times 10^{-19} \ J)$

The energy of one mole of photons of radiation of frequency $2 \times 10^{12} \ Hz$ in $J \ mol^{-1}$ is $.....$ (Nearest integer) (Given: $h = 6.626 \times 10^{-34} \ Js$,$N_A = 6.022 \times 10^{23} \ mol^{-1}$)

The energies $E_1$ and $E_2$ of two radiations are $25 \ eV$ and $50 \ eV$ respectively. The relation between their wavelengths,i.e.,$\lambda_1$ and $\lambda_2$,will be:

What is the speed of all types of electromagnetic radiation in a vacuum? What is it called?

$A$ photon-sensitive metal is not emitting photoelectrons when irradiated. It will do so when the threshold is crossed. To cross the threshold,we need to increase: