Question 3-19C2

The photoconductive effect describes how the electrical conductivity of certain materials, primarily semiconductors, increases when exposed to light. When photons of sufficient energy strike the semiconductor material, they energize electrons, causing them to break free from their atomic bonds and move into the conduction band. This process creates additional free electrons and "holes" (a type of positive charge carrier). The presence of more free charge carriers reduces the material's electrical resistance, thus increasing its conductivity. Option A describes the photovoltaic effect, where light energy is directly converted into voltage (electromotive energy), as seen in solar cells, rather than just an increase in conductivity. Option C describes the emission of light, such as from an LED, which is the opposite conversion. Option D is incorrect because the photoconductive effect causes an *increase*, not a decrease, in conductivity.