Q: In this task you will be given a text passage from a trivia quiz. You should choose the category this question belongs to from these categories: History, Science, Social Science, Fine Arts, Literature. You can only choose one category, so if in doubt, please choose the closest match.
This effect dominates in energy regimes under one mega-electron volt, while at higher energies Compton scattering and pair production are likely to occur. It was first observed by Heinrich Hertz while working with spark gaps. Mathematically, this effect is likely to occur when the threshold frequency of the electromagnetic radiation times Planck's constant is equal to the work function, usually represented by a lower case phi. For 10 points, name this effect where incident light on the surface of a metal releases electrons.
A:
Science