A photocell is a device which
A) Absorbs light and produces a stream of electrons.
B) Absorb a stream of electrons and produce light.
C) Converts protons into photons.
D) Converts photons into protons.

Hint: Photocell is an optoelectronic device that works on the principle of photoelectric effect. It is mainly used to detect light of suitable wavelength.

Complete answer:
Photocells produce energy by the process of photoelectric effect. The photoelectric effect is when particles of light called photons strike the surface of a metal and an electron from the metal is ejected. The energy of incident photons is transferred to the kinetic energy of the escaping electron and some of it goes into removing the electron which is called the work function of a metal used in photocell.

Hence, option (A) is the correct answer.

Note: Photocells are also called photoelectric cells because of its working principle. There are basically three types of Photoelectric cell:-
Photo-emissive cell:- It is a type of gas-filled or vacuum tube that is sensitive to light based on the principle of photoelectric field.
Photo-voltaic cell:-The photocell whose working is based on an inner photoelectric cell. It is also called a true cell because it generates e.m.f without the application of any external potential.
Photo-conductive cell:- The photoconductive cell is a two terminal resistance linearly varying with the intensity of then incidence light.
Applications of Photoelectric cells are:-
1. It can be used for automatic operation of switching on and off the street light.
2. It can be used in obtaining electrical energy from sunlight energy.
3. They are used for producing sound in cinematography.
4. It can be used to study the temperature and spectra of stars.