• Tags: photocell, applications, technology
• Difficulty: Foundation

Photocells (photoelectric cells) convert light energy to electrical energy using the photoelectric effect. Types: photoemissive (electrons ejected from cathode), photoconductive (resistance changes with light — LDR), and photovoltaic (generates EMF directly — solar cell).

Applications: burglar alarms, automatic door openers, light meters in cameras, sound reproduction from film tracks, solar cells, smoke detectors, photomultiplier tubes (for detecting single photons). The photoelectric effect is also the basis for X-ray photoelectron spectroscopy (XPS) used in material science.

JEE rarely tests applications directly but may include conceptual questions about how photocells work or why certain metals are preferred (low work function metals like Cs for visible light detection).