Why Does a Stick Seem to Bend When Put in Water?
When light passes from one medium to another, as for example from glass or water to air, or from air or glass to water, the rays of light change their course, thus making them seem to be bent or broken. The rays of light from the part of the stick in the water take a different direction from the rays from the part which is out of the water, giving the appearance of breaking or bending at the place where the air and water meet. It is, of course, the light rays which are bent and not the object itself.
This bending or changing of the path of light rays is called refraction. If you place a coin in a glass of water so that it may be viewed obliquely, you can apparently see two coins, a small one through the surface of the water and another apparently magnified through the side of the glass.
This is due only to the absolute principle that rays of light change their direction in passing from one thing to another, and on this principle of the rays of light our optical instruments, including the microscope, the telescope, the camera and eyeglasses are based.