The energy of an electron in the excited hydrogen atom is $-3.4 \ eV$. Then according to Bohr's theory,the angular momentum of the electron in that excited state is ($h=$ Planck's constant).

The ratio of the area enclosed by the second orbit to the first orbit is ......

For the Balmer series in the spectrum of $H$ atom,$\bar{v}=R_{H}\left\{\frac{1}{n_{1}^{2}}-\frac{1}{n_{2}^{2}}\right\}$,the correct statements among $(I)$ to $(IV)$ are:
$(I)$ As wavelength decreases,the lines in the series converge.
$(II)$ The integer $n_{1}$ is equal to $2$.
$(III)$ The lines of longest wavelength corresponds to $n_{2}=3$.
$(IV)$ The ionization energy of hydrogen can be calculated from wave number of these lines.

The series limit for the Balmer series of $H$ atom spectra is:

For a lithium atom,what can be said about the angular momentum and energy values for the permitted orbit of its third electron?

If the energy of a photon with a frequency of $2 \times 10^{12} \ Hz$ is $E$,then the energy of a photon with a frequency of $4 \times 10^{12} \ Hz$ will be ....