Conduction occurs either by the movement of electrons or the movement of ionic atoms or molecules. Conductors always have a very small amount of resistance to electrical conduction. Semiconductor A material that will conduct a small amperage of electricity when the voltage exceeds some critical value. This minimum necessary voltage corresponds to the energy necessary to excite electrons from a filled energy level called the valence band to an unoccupied energy level called the conduction band. This energy difference is called the band gap.
Intrinsic semiconductors are materials which have a small band gap in their pure form.
Superconductor Certain materials at very low temperatures will have a state with no resistance to electrical conduction. The exact means by which this occurs is not yet completely understood. The opacity will depend upon the wavelength of light also. Refraction Refraction is the bending of light rays. The amount of bending is different for different substances and different wave lengths of light.