Intensity vs Current
Higher intensity → more photoelectrons → higher saturation current. Same V_s across intensities.
Key Notes
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.
Formulas
Photocurrent (saturation)
η = quantum efficiency; N_photons = photons/sec arriving.
Photon flux from intensity
I = intensity (W/m²); A = area; hf = energy per photon.
Intensity dependence
Linear, for given f > f₀.
Important Points
Intensity controls QUANTITY (number of electrons). Frequency controls QUALITY (energy per electron).
Doubling intensity at the same f doubles the photocurrent. Doubling intensity below f₀ still produces ZERO current.
Saturation occurs when anode voltage is high enough to collect every electron — current then becomes I_max independent of V.
Below saturation, some photoelectrons turn back due to space-charge or low anode-attraction.
Solar cells exploit this: more sunlight (higher I) → more photoelectrons → more current.
Quantum efficiency η is < 1 in reality — not every photon ejects an electron (reflection, deeper absorption losses).
Intensity vs Current notes from sciphylab (also known as SciPhy, SciPhy Lab, SciPhy Labs, Physics Lab). Class 12 physics revision for JEE Mains, JEE Advanced, NEET UG, AP Physics 1/2/C, SAT, and CUET-UG.