Retro-reflector or mirror retroreflector
Purpose of the experiment:
How to position flat mirrors in order to obtain a retroreflector, i.e. a system that reflects light directly to the sender regardless of the direction from which the light falls.
List of materials:
- three square, flat mirrors of any size (for design considerations it would be good if the mirror edge was approx. 10-20 cm)
- sticky tape or plasticine (for temporary bonding of the mirrors)
- a laser pointer or a torch with a concentrated beam of light
- Position two mirrors and join their edges together (you can bond them using sticky tape of plasticine).
- Illuminate one of the mirrors with laser light or a torch.
- Change the relative positioning of the mirrors so that the light should be reflected towards the source of light (laser, torch) regardless of the direction of illumination.
- Build a similar system using three mirrors
Questions to the experiment:
- By means of what other optical elements can the retroreflector effect be achieved?
- Where are reflexive elements (retroreflectors) used?
Description of the phenomenon:
Interpretations of results:
For mirror reflection on any surface, the angle of reflection is the same as the angle of incidence; what is more, both light rays move on the same plane. If two mirrors touch each other along the edges forming an angle of 90 degrees, then regardless of the angle of incidence, after being reflected twice the light will propagate in the same direction from which it fell; the only condition is that the light ray should move in the plane perpendicular to the surface of the both mirrors. This limitation does not apply when three mirrors are used and each of them is positioned perpendicularly to the other two. In a retroreflector of this type there are typically three reflections on three mirrors.
- Reflective elements are made up of mini retroreflectors that reflect light and increase visibility, e.g. on the road.
- In order to improve safety, since 1st September 2014 pedestrians moving on roads outside built up areas have been obliged to wear reflexive elements after dark.