Correct Answer: Thermopile

Solution : The correct option is thermopile.

A thermopile is an instrument that detects radiant heat. It's a device that transforms heat energy into electrical energy. A thermopile is composed of many thermocouples, which are devices that translate temperature differences into electrical voltage. The thermocouples are linked in series, and the thermopile's output voltage is proportional to the quantity of radiant heat incident on it.