Which one of the following metals is used in the filaments of photo-electric cells that convert light energy into electric energy ?

Photoelectric cells convert light energy into electrical energy using the photoelectric effect, where light incident on a metal surface causes the emission of electrons. For efficient conversion in the visible light spectrum, metals with low work functions are required. Alkali metals like rubidium, cesium, and potassium are ideal because their valence electrons are loosely bound, allowing for easy photoemission. While tungsten is commonly used as a filament in incandescent bulbs or thermionic tubes due to its high melting point, it has a high work function and is not suitable for the light-sensitive surfaces of standard photocells. Rubidium, specifically, is used in the photoemissive coatings (often referred to as the sensitive 'filament' or cathode surface) of photoelectric cells to ensure high sensitivity to light [1].

Sources

1. [1] https://ntrs.nasa.gov/api/citations/19700009387/downloads/19700009387.pdf