12.1 What is Refraction?

 The bending or change in direction of light when it travels from one medium to another.

Analogy: A car rolling from pavement onto sand.

The speed of light in vacuum: c = 3.00 × 10 8 Speed of light in a medium: ( v ) is different for different materials Medium (Material)Speed of Light Vacuum (Nothing in the way!!) 3.00 x 10 8 m/s Water 2.26 x 10 8 m/s Acrylic (Fiber in sweaters and hats, etc.) 1.76 x 10 8 m/s

Rule #1: The incident ray, normal and refracted ray are all in the same plane.

Rule #2: Light bends towards the normal when its speed decreases in a material. 7 Bends Towards the Normal Medium 2 will have a slower speed of light

Rule #3: Light bends away from the normal when the speed increases in a material. 8 Bends away from the Normal Medium 2 will have a greater speed of light

9  Light from the spoon travels from water to air and will bend away from the normal.  Our brain assumes light travels straight and projects a virtual image into the water in a different location.  Therefore, the spoon appears displaced, while it’s only refracted.

10  Refraction is often accompanied by reflection – called partial reflection and refraction.  Eg. Light striking water or a window  Two-way mirrors and mirrored sunglasses reflect much of the incident light.

 The ratio of the speed of light in a vacuum to the speed of light in that medium.  Formula: Where:  n is the index of refraction  c is the speed of light (vacuum) (always 3.00x10 8 m/s)  v is the speed of light in a given medium. The index of refraction has no units (both m/s speeds cancel)

 Using the angle of incidence and the angle of refraction the index of refraction can also be calculated n = Index of Refraction i = angle of incidence R = angle of refraction

The speed of light in glass is 1.52 x 10 8 m/s. What is the Index of Refraction for glass?? Given: c = 3.00 x 10 8 m/s v = 1.53 x 10 8 m/s n = ? n = 3.00 x 10 8 m/s 1.53 x 10 8 m/s n = 1.96 Therefore, the index of refraction of glass is 1.96.

Given: c = 3.00 x 10 8 m/s v = 2.25 x 10 8 m/s n = ? n = 3.00 x 10 8 m/s 2.25 x 10 8 m/s n = 1.33 Therefore, the index of refraction of water is 1.33 The speed of light in water is 2.25x10 8 m/s. Determine the index of refraction.

Therefore, the index of refraction of ice is 1.37 A ray of light is passing from water into ice. If the angle of incidence of light in water is 40 degrees and the angle of refraction in ice is 28 degrees what is the index of refraction? Given i = 40º R = 28º n = ? n = sin 40 º sin 28 º n = n = 1.37