Concept:The photoelectric effect is applied when light energy is converted into an electric current or is used to control a circuit.
Explanation:Situation I involves processing sound in films, which uses photoelectric cells to turn changing light into electrical signals; hence it employs the photoelectric effect.
Situation II involves automatic street lighting, where photoelectric cells detect decreasing daylight and switch the lights on; thus it also uses the effect.
Situation III is reproduction of sound by a telephone, which relies on electrical signals rather than light, so it does not use the photoelectric effect.
Situation IV is the production of current in a solar cell, which works by the photovoltaic form of the photoelectric effect.
Therefore, the situations that correctly apply the photoelectric effect are I, II, and IV.
Answer:I, II and IV only, which is Option A.