The energy of an electron in the first Bohr orbit of the hydrogen atom is $-13.6 \ eV$. Calculate the energy of an electron in the first Bohr orbit of $He^{+}$ in $eV$.

For the $H$ spectrum,the limiting line in the $Balmer$ series has a frequency of ...... $(R_\infty = 3.29 \times 10^{15} \text{ cycles/s})$

State the uses of atomic spectra.

The value of Rydberg constant $\left(R_H\right)$ is $2.18 \times 10^{-18} \ J$. The velocity of an electron having mass $9.1 \times 10^{-31} \ kg$ in Bohr's first orbit of a hydrogen atom $= \dots \dots \dots \times 10^5 \ ms^{-1}$ (nearest integer).

Bohr’s atomic theory gave the idea of :

The ratio of the energy of the electrons in the ground state of hydrogen to the electrons in the first excited state of $Be^{3+}$ is: