Final answer:
A photographic plate is a permanent, visible image produced by radiation passing through a material being tested. Photographic film is commonly used as a detector of ionizing radiation, such as in medical X-rays.
Step-by-step explanation:
A photographic plate is a permanent, visible image on a recording medium produced by penetrating radiation passing through a material being tested. Photographic film, which contains a light-sensitive chemical coating, is commonly used as a detector of ionizing radiation, such as in medical and dental X-rays. When radiation interacts with the film's emulsion, it chemically alters it, resulting in a darkening of the film.