Final answer:
Night-vision goggles detect infrared radiation, allowing the wearer to see in the dark by converting this radiation into a visible image, often to identify warm objects that emit or reflect infrared light.
Step-by-step explanation:
Someone wearing night-vision goggles can detect infrared radiation. These goggles use special sensors to pick up on infrared light, which is not visible to the human eye. The sensors detect the infrared light emitted or reflected by objects and convert it into a visible image, allowing the wearer to see in low-light conditions or even in total darkness.
Infrared radiation is efficiently emitted and absorbed by water molecules, as they rotate and vibrate particularly well at these frequencies. The human body, being warm and composed of a significant amount of water, has a high emissivity in the infrared range (e=0.97). Night-vision goggles harness this property to identify warm objects, like humans, based on the infrared radiation they emit.