The law of reflectionEdit
This is the most important rule to do with reflection:
Angle of incidence = Angle of reflection
A periscope uses reflection - there are two mirrors at 45o. This means the user can see much higher than normal, as light rays come in, hit the mirror, hit the other mirror and then finally, reach the eye. In more elaborate periscopes, prisms replace mirrors - however, this needs another phenomena - total internal reflection.
Total internal reflectionEdit
Total internal reflection is when light hits a medium at an angle that is greater than the critical angle. The critical angle is the angle of incidence of which above, total internal reflection occurs.