22.2.2—The terms threshold frequency and threshold wavelength

Threshold frequency f₀ is the minimum photon frequency that ejects electrons; threshold wavelength λ₀ is the maximum wavelength, related by c=f₀λ₀.

Below f₀ or above λ₀ no electrons are emitted regardless of intensity in the ideal model.

A metal with threshold frequency 6.0×10¹⁴ Hz has threshold wavelength about 500 nm.

Threshold frequency is not the frequency of emitted electrons, and higher intensity cannot compensate for lower photon frequency.