The conduction band is the band of electron orbitals that electrons can jump up into from the valence band when excited. When the electrons are in these orbitals, they have enough energy to move freely in the material. This movement of electrons creates an electric current.

Are electrons free in the conduction band?

Also, the electrons in the conduction band are free to move around the material with little resistance, while in the valence band the electrons are usually bound to the parent atom/molecule, but they do have some degree of freedom, just not as much as the conduction electrons. Look up valence band on wikipedia.

How do you determine the number of electrons in a conduction band?

The total number of electrons in the conduction band, N_cb, can then be obtained by integrating the above function from the bottom of the conduction band upward.