Which device is used to detect infrared radiation?

A photodiode is the correct choice for detecting infrared radiation because it is specifically designed to respond to light, including wavelengths in the infrared spectrum. When infrared radiation hits the photodiode, it generates a small electrical current that can be measured. This characteristic makes photodiodes ideal for applications that require the detection of infrared signals, such as remote controls, optical communications, and various sensing technologies.

While thermometers measure temperature changes often caused by infrared radiation, they do not directly detect or convert infrared light into an electric signal. Geiger counters are instruments for detecting ionizing radiation, such as alpha and beta particles and gamma rays, not infrared radiation. CCD cameras, while capable of capturing images, are typically more responsive to visible light than to infrared wavelengths unless specifically designed for such purposes using filters or specialized sensors. Therefore, photodiodes are the most appropriate choice for direct detection of infrared radiation.