Question

Why are the shells in which electrons revolve also called energy levels?

Answer 1

Each orbit has a definite energy which can be calculated . The energy of an electron remains constant as long as it revolves in a particular orbit. An electron absorbs energy while jumping from a lower energy level to a higher energy level and an electron gives out energy while jumping from a high energy level to a lower energy level.Therefore they are also called energy levels.

Answer 2

 the shells in which electrons revolve also called energy levels, because when an electron gains enough energy (usually done by introducing electricity) it rises to the next energy level.