Why some materials transmit light n some not?
Opaque materials are by definition materials which cannot transmit light. Transparent materials are by definition materials which do transmit light. There are three optical properties coming in to play, unique at every value of frequency. They are as follows: reflectivity, transmissivity, and emissivity. Only two of these properties are independent, because they all must add up to 1. For any opaque material, transmissivity is zero. Emissivity and reflectivity combined determine if the material reflects or absorbs. Why is the absorbing property called emissivity…not absorptivity? Well, it can be called either. As per Kirchhoff’s law of radiation, these two properties are equal at any given value of frequency. It is just that emissivity is more documented. Why is this so? Unfortunately you cannot receive as real of an answer as you might like. Some materials have molecules which are “in tune” with each frequency and therefore tend to reflect the light. If molecules are not “in tune”, t
