In the Franck-Hertz experiment, the first dip in the current-voltage graph for hydrogen is observed at $10.2 \, V$. The wavelength of light emitted by the hydrogen atom when excited to the first excitation level is $\qquad$ $nm$.
(Given $hc = 1245 \, eV \cdot nm$, $e = 1.6 \times 10^{-19} \, C$).

Consider a hydrogen-like ionized atom with atomic number $Z$ with a single electron. In the emission spectrum of this atom,the photon emitted in the $n = 2$ to $n = 1$ transition has energy $74.8 \ eV$ higher than the photon emitted in the $n = 3$ to $n = 2$ transition. The ionization energy of the hydrogen atom is $13.6 \ eV$. The value of $Z$ is:

The ratio of the radius of the first Bohr orbit to that of the second Bohr orbit of the orbital electron is

The energy of an electron in the ground state of a hydrogen atom is $E$. What is the energy of an electron in the $2^{nd}$ excited state of $Li^{++}$?

In the Bohr model of the hydrogen atom,the angular velocity $\omega_n$ of the electron depends on the principal quantum number $n$ as:

Consider an electron in a hydrogen atom,revolving in its second excited state (having radius $4.65 \, \mathring{A}$). The de-Broglie wavelength of this electron is .... $\mathring{A}$.