Behavioural characteristics of light: Reflection and Refraction
The two most observable behavioural characteristics of light are reflection and refraction. This hub attempts to investigate reflection and refraction of light, and its application in everyday living.
Reflection is the bouncing of light off a surface, the simplest example being the reflection of a laser beam off a mirror. When illustrating the reflection of light it is essential to draw in a ‘Normal’ line; 90o to the reflective surface. Light is travels in a straight line and is represented as a singular line when demonstrating reflection.
When light reflects off a plane mirror, the angle of incidence is equal to the angle of reflection - mathematically: i = r, as in the diagram below. (The angles of incidence and reflection is the angle measured between the ray and the normal).
Reflection of light acts in the same manner when being reflected off concave or convex mirrors (i = r), but due to the curvature of the reflective surface, causes the light to focus (whether it be internally or externally).
In concave mirrors, light is directed into a focal point within the curve of the mirror. Examples of their practical application are anywhere where beams of light must be focused, such as dentist's mirrors, torches or headlights.
Convex mirrors disperse the rays of light, with the focus actually located within the curve. Their application is anywhere where an extended field of view is needed, such as mirrors in parking lots and in buses.
The diagrams below illustrate reflection of light from a concave and a convex mirror.
Refraction of light involves the 'bending' of light as it travels from one medium to another, and is the result of a change in the velocity of light. An example of this 'bending' can be seen with a spoon placed in a glass of water.
When travelling from one medium into a denser medium, the light bends towards the normal (and vice versa). The refraction of light obeys Snells law: Sin i/Sin r = n2/n1 = v1/v2 = π1/π2. The refractive index (n) for a wave travelling from one medium to another is the ratio of the sine of the angle of incidence to the sine of the angle of reflection. The refractive index is indicitive of the amount of bending (change in velocity) that will occur; the refractive index of light in a vacuum being equal to 1.
Total Internal Reflection
Total internal reflection occurs when light moves from a transparent medium into air and bends so much it is totally internally reflected (as shown by the blue ray in the diagram to the right).
There are two conditions that must be met for total internal reflection to occur:
- The internal medium has a higher refractive index than the external medium.
- The angle of incidence must exceed the critical angle (i > c).
The popularity of total internal reflection for communication purposes has steadily increased over the last several years, as light can travel considerably faster than electricity, and significanly more information can be encoded. Total internal reflection is used in technology such as firbe optic cables.