Key Concepts: Photoelectric Effect

The Photoelectric Effect

• Light shining on a metal surface can eject electrons — these are called photoelectrons.
• This effect could not be explained by classical wave theory.

Key Observations

• There is a threshold frequency (f₀) below which no electrons are emitted, regardless of intensity.
• Above f₀, increasing intensity increases the number of electrons but not their maximum KE.
• Increasing frequency increases the maximum KE of emitted electrons.
• Emission is instantaneous — no time delay.

Einstein's Explanation

• Light consists of photons, each with energy E = hf.
• KE_max = hf − φ, where φ = hf₀ is the work function (minimum energy to free an electron).
• Below the threshold frequency, no single photon has enough energy to eject an electron.