Photoelectric Effect Time Response

NCERT emphasizes that in the photon picture, photoemission is essentially instantaneous because a single photon delivers all its energy to a single electron in one discrete quantum interaction. There is no need for energy to build up gradually, so provided the photon frequency exceeds the threshold, an electron can be ejected within about $10^{-9}$ seconds of illumination. This immediacy directly contradicted the classical wave prediction and strongly supported Einstein's quantum model. The option about slowly accumulating wave energy is wrong because it is the discredited classical view that would predict a measurable time lag, which experiments never observed. The option about the metal heating first is wrong because photoemission is not a thermal process and occurs even for feeble beams. The option about many photons collectively energizing an electron is wrong because a single sufficiently energetic photon suffices, and multi-photon effects are negligible at ordinary intensities. As stated in NCERT Class 12, Chapter 11, the absence of a time lag is a hallmark of the particle nature of light. A consistency check confirms that one-photon, one-electron energy transfer naturally explains the observed instantaneous emission.