01Light as particles
Light shining on a metal ejects electrons only if each photon has enough energy (above a threshold frequency). Brighter light below threshold does nothing.
Above threshold, extra photon energy becomes kinetic energy of the electron; brighter light ejects more electrons, not faster ones.
02Notebook box
KE_electron = hν − work function.
Worked example: Red light ejects nothing; dim UV ejects electrons. Why? Photon energy, not intensity, matters.