The minimum energy required to free an electron from the surface is called the work function.

The minimum energy required to free an electron from the surface is called the work function.

• A. Electron affinity
• B. Band gap energy
• C. Activation energy
• D. Work function

Answer: (D)

The minimum energy to free an electron from a surface is the work function. It’s the energy barrier at the solid’s surface that an electron must overcome to escape into vacuum. This value is a property of the material and its surface condition, and it’s typically a few electron-volts for metals. In practice, it explains why light or heat must supply at least this energy to cause emission, and in the photoelectric effect the photon energy must be at least φ, with any extra becoming the ejected electron’s kinetic energy. Other terms describe different situations: electron affinity relates to adding an electron to a neutral atom in the gas phase, band gap energy is the energy separation between valence and conduction bands in a solid, and activation energy is the barrier to a chemical reaction—not the escape of a surface electron.

The minimum energy to free an electron from a surface is the work function. It’s the energy barrier at the solid’s surface that an electron must overcome to escape into vacuum. This value is a property of the material and its surface condition, and it’s typically a few electron-volts for metals. In practice, it explains why light or heat must supply at least this energy to cause emission, and in the photoelectric effect the photon energy must be at least φ, with any extra becoming the ejected electron’s kinetic energy. Other terms describe different situations: electron affinity relates to adding an electron to a neutral atom in the gas phase, band gap energy is the energy separation between valence and conduction bands in a solid, and activation energy is the barrier to a chemical reaction—not the escape of a surface electron.