What happens when an electron moving from the 3rd energy level to the 1st energy level?

A photon of wavelength 103 nm is released

Explanation:

When an electron in an atom jumps from a higher energy level to a lower energy level, it releases a photon whose energy is equal to the difference in energy between the two levels.

For example, if we are talking about a hydrogen atom, the energy of the levels are:

So, the energy of the photon released when the electron jumps from the level n=3 to n=1 is

In Joules,

We can also find the wavelength of this photon, using the equation:

heat the gas and measure the pressure