A photoelectric cell is primarily used to convert what type of energy?

A photoelectric cell, also known as a photovoltaic cell, is specially designed to convert light energy directly into electrical energy. This process involves the photoelectric effect, where photons from light strike the cell and excite electrons, creating an electrical current. This technology is foundational for solar panels, which harness sunlight to generate electricity.

The other forms of energy mentioned—heat, sound, and motion—are not the primary focus of photoelectric cells. While there are technologies that can convert heat into electricity (thermoelectric generators) or sound into electricity (microphone technology), and motion into electricity (mechanical generators), these do not pertain to the functioning of a photoelectric cell. Therefore, the correct answer is based on the specific role of photoelectric cells in the context of energy conversion.