Intensity vs Current

Photoelectric current (number of electrons per unit time × charge) is DIRECTLY proportional to intensity, for given frequency above threshold.

Doubling intensity doubles the rate of photons hitting the surface ⇒ doubles the rate of photoelectron emission ⇒ doubles the saturation current.

Intensity does NOT affect: K_max, threshold frequency, stopping potential.

This proportionality is exact in the photon picture: I = (photon rate)·hf. Doubling I doubles photon rate, hence emission rate.

Saturation current: at high anode voltage, every photoelectron is collected. Saturation level scales with I.

Below saturation (low voltage), some electrons return to the cathode without crossing — current is sub-saturation.

Photodetectors, solar cells, light meters — all rely on the intensity-current proportionality.