The correct answer is: B. Photovoltaic cell.
A photovoltaic cell, also known as a solar cell, is a device that converts light into electricity. It is a semiconductor device, meaning that it is made from a material that has electrical conductivity between that of a conductor and an insulator. When light hits a photovoltaic cell, it excites electrons in the semiconductor material. These excited electrons are then able to move through the material, creating an electric current.
Photovoltaic cells are used in a variety of applications, including solar panels, calculators, and wristwatches. They are also being used to generate electricity on a large scale, as part of the effort to transition to renewable energy sources.
The other options are incorrect for the following reasons:
- A photodiode is a semiconductor device that converts light into an electrical signal. It is used in a variety of applications, including optical communication, light detection, and solar cells.
- A thermocouple is a device that converts heat energy into electrical energy. It is made from two dissimilar metals that are joined together. When the junction is heated, an electric current is generated. Thermocouples are used in a variety of applications, including temperature measurement, temperature control, and power generation.
- A heliostat is a device that reflects sunlight to a single point. It is used in solar power plants to concentrate sunlight on a photovoltaic cell or solar thermal collector.