Behaviour of Light



and



Light can be absorbed, reflected or transmitted.



absorbed



reflected



transmitted



We are able to see the tree because light is reflected into your eyes. We see reflected light.



A beautiful example

of natural reflection!



Notice that the angle of the ball hitting the wall appears to be equal to the angle of the ball moving away from the wall.



rough surface



REFRACTION - Refraction occurs when the light ray changes mediums. Light traveling through air and then going through water is an example of a light ray changing medium. The speed of the light ray changes when it enters a different medium. In most cases the direction of the light also changes. We say the light bends. Depending on the new medium the light will travel faster or slower. It is the different densities that causes the ray to slow down or speed up which then causes it to bend. Light rays slow down about 25% when passing through water and 35% when passing through glass. If the light travels slower then this medium is called the denser medium . If the light ray travels faster then the medium is called the rarer medium . When light enters a denser medium the ray bends toward the normal - when light enters a rarer medium it is bent away form the normal.



light bends quite a bit in water



refraction at work



bj



page 3 of 5



Reflection



Refraction



Back to electromagnetic spectrum, colour and waves p.2



To mirrors, lenses and your eyes p.4



Reflection



Reflection : If an object does not emit its own light, it must reflect light in order to be seen. Reflection involves two rays - an incoming or incident ray and an outgoing or reflected ray. If we draw a line perpendicular to a flat surface, this line is said to be the normal. A ray of light that hits this surface is called the incident ray. This ray of light hits the surface and bounces off ( reflected ray ). The angle between the incident ray and the normal will be identical in measurement as the angle between the reflected ray and the normal. All reflected light obeys this relationship, called Snell's Law, that the angle of incidence equals the angle of reflection. This is the Law of Reflection. Reflection from a smooth, mirror-like surface is called specular . If the surface is rough, the rays of light are reflected in many directions. The angles of incidence and reflection are still equal but the rays appear to be scattered. This is diffuse reflection. This diffuse reflection is how we can see illuminated objects.



smooth surface



Angle of Incident = Angle of Reflection



-with permission from Dr. Steven Shropshire,

Department of Physics, Idaho State University

