threshold frequency

Threshold frequency is the minimum frequency of light needed to eject electrons from a material, typically a metal. When light hits a metal surface, it can transfer energy to electrons. If the light’s frequency is below this threshold, the electrons won't gain enough energy to escape. If the frequency meets or exceeds the threshold, electrons can be released, creating a flow of electric current. Essentially, it's the smallest "color" or frequency of light that can stimulate electrons to leave the material's surface. This concept is fundamental in understanding the photoelectric effect and the quantum nature of light.