What force causes light to reflect off a surface?
Answers
Reflection happens at the interface between two mediums with significantly different properties. For example, the conductivity of metal is very different from the conductivity of vacuum, so you will get reflection from a mirror in air. In this case, the high conductivity of the metal allows a current to flow in response to the e-field of the EM wave, and that current acts as the source of its own EM wave which is the reflected wave. In order for this to occur the surface must be smooth at the level of a wavelength of the EM wave, so for visible light this phenomenon is due to the collective behavior of many particles in the reflector. Most of the properties of solids (like metal) are not due to the behavior of the individual atoms, but rather due to their collective behavior.