The total energy of an electron in the first excited state of the hydrogen atom is $-3.4 \ eV$. Find out its potential energy in this state.

An electron with kinetic energy $E$ collides with a hydrogen atom in the ground state. The collision will be elastic

How much energy is needed to release the electron from the second excited state in the hydrogen atom (in $eV$)?

Some energy levels of a molecule are shown in the figure. The ratio of the wavelengths $r = \frac{\lambda_1}{\lambda_2}$ is given by

The minimum excitation energy of an electron revolving in the first orbit of hydrogen is (in $eV$)

The figure shows the energy levels of a certain atom. When the electron de-excites from $3E$ to $E$,an electromagnetic wave of wavelength $\lambda$ is emitted. What is the wavelength of the electromagnetic wave emitted when the electron de-excites from $\frac{5E}{3}$ to $E$?