What is the photoelectric effect?

• A. The emission of electrons from a metal when light shines on the metal.
• B. The emission of electrons from a non-conductive surface when light shines on it.
• C. The emission of photons from a metal when heated.
• D. The emission of electrons from a metal when light shines on the metal.

Answer: (D)

The photoelectric effect is the ejection of electrons from a metal surface when light shines on it with enough energy per photon. Each photon has energy hf, and an electron can escape only if hf exceeds the metal’s work function phi. When hf > phi, the extra energy (hf − phi) becomes the electron’s kinetic energy. The emission rate depends on light intensity because more photons mean more electrons can be released, while the kinetic energy of the emitted electrons depends on the photon energy, not the light’s intensity. If the light is below the threshold energy, no electrons are emitted regardless of brightness. This phenomenon shows light behaving in particle-like packets (photons) and is captured by the statement describing electrons being emitted from a metal when light shines on it.