What is an "acceptor energy level"?explain.

What is donor energy level?Explain.

A p-type semiconductor has acceptor energy levels 57 meV(millielectron volt) above the valence band.Find the maximum wavelength of the radiation,which can create a hole?

What is Fermi energy level ?

In what part of its orbit is the earth's potential energy greatest with respect to the sun? In what part of its orbit is its kinetic energy greatest ? Explain.

What are energy levels or shells ?