Final answer:
Corner reflectors should be placed where total internal reflection conditions are met to ensure light is reflected back in a parallel direction. They are used in devices like binoculars and periscopes as well as for enhancing safety in transportation.
Step-by-step explanation:
Reflectors, specifically corner reflectors, should be positioned where they can satisfy the conditions for total internal reflection. With the properties of common materials, achieving a critical angle less than 45° is quite feasible, ensuring that light entering the reflector is reflected back parallel to the direction it came from. This is critical in applications such as binoculars and periscopes in submarines, where precise reflection is necessary for optimal performance. Reflectors are also used in other areas for safety; for example, astronauts placed corner reflectors on the Moon for scientific measurements, and they are commonly found on bicycles and vehicles to improve visibility and safety at night.