Why are energy levels (shells) not equally spaced?

Question

Why are energy levels (shells) not equally spaced?

Answer 1

The farther away from the nucleus, the less the positive charge is felt by the electron. This is an exponential effect, and grows with distance. This would be the most elementary way of explaining it, but try this question with physics as well.

Answer 2

The energy of the levels are in the form En = -E1/n^2

this result is correctly demonstrated by quantum chemistry but a simpler explanation lies in Bohr's atom theory

Demonstration in the link