When an electron in a hydrogen spectrum transitions from the $7^{th}$ energy level to the $1^{st}$ energy level,what is the total number of spectral lines produced?

In a hydrogen atom,if $9 \, eV$ of energy is supplied,how many spectral lines will be emitted?

In the Rutherford experiment,if light atoms are used instead of heavy elements,what change is observed in the results?

In astronomical observations,signals observed from the distant stars are generally weak. If the photon detector receives a total of $3.15 \times 10^{-18} \, J$ from the radiations of $600 \, nm$,calculate the number of photons received by the detector.

For a hydrogen atom with $n = 1$,the radius of the Bohr orbit is approximately $0.530 \, \mathring{A}$. What will be the radius for the first excited state $(n = 2)$ in $\mathring{A}$?

The wavelength and frequency of a photon with energy $2 \ eV$ are respectively: