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

What will be the ionization energy in $eV$ for an excited hydrogen atom?

If the velocity of an electron in the $1^{st}$ orbit of the $H$ atom is $V$,then what will be the velocity in the $4^{th}$ orbit of $Be^{3+}$?

Explain the following according to Bohr's model of hydrogen:
$(i)$ Principal quantum number
$(ii)$ Radius of stationary orbit $(r)$
$(iii)$ Energy of stationary state
$(iv)$ Isoelectronic ion of $H$
$(v)$ Velocity of electron

If the wavelength of an electromagnetic radiation is $2000 \ \text{Å}$, what is its energy in ergs?

Calculate the ratio of the radius of the $2^{nd}$ and $3^{rd}$ orbit of a hydrogen atom. (Note: $r_n \propto n^2$)