22.3.1—The photoelectric effect provides evidence for a particulate nature of

Photoemission is evidence that light transfers energy in discrete photons, each with energy E=hf.

The threshold frequency, near-instant emission and intensity–frequency separation are difficult to explain with a purely continuous-wave energy supply.

A low-intensity beam above threshold can eject electrons immediately, whereas a bright beam below threshold cannot in the ideal model.

This evidence supports quantised energy transfer; it does not mean every classical wave description is useless in every context.