8. Write two uses of spherical mirrors.
9. Define the following:
(i) Least distance of distinct vision
(ii)
Persistence of vision.
Answers
1 A concave mirror is used as the reflector in search lights, head lights of motor vehicles, solar cookers, torches and in table lamps. A convex mirror is used in automobiles such as scooters, trucks and buses as rear view mirror to see the traffic behind the vehicle.
2.
a. In optometry, the least distance of distinct vision (LDDV) or the reference seeing distance (RSD) is the closest someone with "normal" vision (20/20 vision) can comfortably look at something. In other words, LDDV is the minimum comfortable distance between the naked human eye and a visible object.
B. Persistence of vision traditionally refers to the optical illusion that occurs when visual perception of an object does not cease for some time after the rays of light proceeding from it have ceased to enter the eye.