The number of absorption lines in the given figure will be .......

If the electron of a hydrogen atom is present in the first orbit, the total energy of the electron is

The work function of a metal $M$ is $6.3 \ eV$. The wavelength of the incident radiation required to just eject the electrons from its surface (in $nm$) is

The work function $(W_0)$ of $Li, K, Mg, Ag$ and $Cu$ are $2.42, 2.25, 3.70, 4.30$ and $4.80 \ eV$ respectively. The number of metals which undergo photoelectric effect if a radiation of wavelength $540 \ nm$ falls on them is $(1 \ eV = 1.602 \times 10^{-19} \ J)$.

Find the value of wave number $(\bar{v})$ in terms of Rydberg's constant,when the transition of an electron takes place between two levels of $He^{+}$ ion whose sum is $4$ and difference is $2$.

Heat treatment of muscular pain involves radiation of wavelength of about $900 \ nm$. Which spectral line of $H$ atom is suitable for this? Given: Rydberg constant $R_{H}=10^5 \ cm^{-1}, h=6.6 \times 10^{-34} \ J \ s, c=3 \times 10^8 \ m / s$.