$A$ $124 \ W$ bulb converts only $15 \ \%$ of the energy supplied to it into visible light of wavelength $640 \ \text{nm}$. How many photons are emitted by the light bulb in one second?

The electron in the $n^{th}$ orbit of $Li^{2+}$ is excited to $(n+1)$ orbit using the radiation of energy $1.47 \times 10^{-17} \ J$. The value of $n$ is $....$. Given $R_H = 2.18 \times 10^{-18} \ J$.

What is the energy associated with the first orbit of $Li^{2+}$ $(R_{H} = 2.18 \times 10^{-18} \ J)$?

When a hydrogen atom in an excited state undergoes electronic transitions to the ground state,$5$ spectral lines are observed in the ultraviolet region. How many spectral lines will be observed in the infrared region due to transitions from the same excited state?

In which hydrogen-like ion is the difference in wavelength between the first line of the Balmer series and the first line of the Lyman series equal to $59.3 \ nm$? $[R_H = 109678 \ cm^{-1}]$

The wavelength of a spectral line for an electronic transition is inversely related to