The ratio of the energy of a photon of $2000 \ \mathring{A}$ wavelength radiation to that of $4000 \ \mathring{A}$ radiation is

The radius of the second Bohr orbit,in terms of the Bohr radius,$a_{0}$,in $Li^{2+}$ is

The binding energy of an $e^-$ in the ground state of a hydrogen atom is $13.6 \ eV$. The energy required to remove an electron from the ground state of a $He^+$ ion is:

The postulate of Bohr theory that electrons jump from one orbit to the other,rather than flow,is according to:

The ground state energy of hydrogen atom is $-13.6 \ eV$. The energy of the second excited state of $He^{+}$ ion in $eV$ is:

$A$ metal surface is illuminated by light of two different wavelengths $248 \ nm$ and $310 \ nm$. The maximum speeds of the photoelectrons corresponding to these wavelengths are $u_1$ and $u_2$ respectively. If the ratio $u_1 : u_2 = 2 : 1$ and $hc = 1240 \ eV \ nm$,the work function of the metal is nearly $:-$ (in $eV$)