Which term describes the emission of electrons from a material surface when it is illuminated by light?

• A. Refraction
• B. Diffraction
• C. Photoelectric effect
• D. Absorption

Answer: (C)

The emission of electrons from a material surface when it is illuminated by light is described by the photoelectric effect. When photons strike the surface with enough energy (hv greater than the material’s work function φ), they transfer energy to electrons, giving some enough energy to overcome their binding and escape. This energy balance is often written as hv = φ + KE of the ejected electron, explaining why there is a threshold frequency and why increasing light intensity (above threshold) increases the number of emitted electrons but not their maximum kinetic energy.

The other terms don’t describe this process: refraction is the bending of light as it changes speed at a boundary, diffraction is the spreading and interference of light around obstacles or openings, and absorption is the uptake of light energy by the material without necessarily ejecting electrons.