Description:

When the light beam hits the water stream, the laser light gets reflected inside the stream. Remember the surface of water is reflective both on its surface and below the surface. When light leaves a denser material, it will change directions. However when the critical angle is reached it will reflect back. Critical angle is the smallest angle of incidence for which light is totally reflected. Total internal reflection happens when a wave strikes a medium boundary at an angle larger than a critical angle, with respect to the normal to the surface. Critical angle of water is 48.8 degrees. When the angle of the beam crosses the critical angle the light does not go out of the stream and total internal reflection takes place. the water is a denser medium than air, and when the laser light is shone into the water, the light then creates total internal reflection. when the water picks up speed and flows out of the hole in the water bottle, and the light stays trapped in the stream. the beam of light then reflects on the under and top sides of the water stream.