The diagram shows niels bohr’s model of an atom.
what happens when the electron moves from the first energy level to the second energy level?

When the electron moves from the first energy level to the second energy level it absorbs a quantum of energy.

Explanation:

According to Bohr's atomic model, electrons move in circular orbits with constant energy. When an electron absorbs a quantum of energy (a discrete amount) it moves from a lower level to a higher level. Conversely, when an electron goes from a higher level to a lower level it releases a quantum of energy. The amount of energy absorbed or released (E) can be calculated through the Planck's-Einstein equation:

E = h . ν

where,

h is the Planck's constant

ν is the frequency of the radiation absorbed or emitted.