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

 Refraction is due to changes in the speed of light.  Different media slow down light by different amounts.  The more the light slows down the more the light is refracted.  When light from the straw passes from the water into the air the light rays are bent.

Analogy: A car rolling from pavement onto sand.

 Makes it difficult to judge the actual location of an object that is in a different medium with respect to the viewer 5

6  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.

 The speed of light in vacuum of space = 300 million m/s or 3.0 x 10 8 m/s, denoted by the constant c  The particles in a medium slow down the passage of the waves, which results in light traveling more slowly through a block of glass, for example, than it travels through a vacuum. 7

 Light refracts only at the boundary when it is entering or leaving a medium. 8

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 (No particles to interact with the light) 3.00 x 10 8 m/s Water 2.26 x 10 8 m/s Acrylic (Plastics) 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. 11 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 material. 12 Bends away from the Normal Medium 2 will have a greater speed of light

 Rule #4: When the angle of incidence is zero, there is no refraction. (No change in direction, yes a change in speed) 13

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15  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.

 In addition to the incident ray and the reflected ray, there is now a third ray called the refracted ray  The refracted ray is the one that bends upon entering a second medium.  The angle of refraction is the angle between the normal and the refracted ray.  Its symbol is the upper-case R.

17 At the boundary of two mediums, some of the light is reflected while the rest is refracted.

 The process of separating colours by refraction.  Blue light bends more than red light  blue light must travel slower than red light.  Only in a vaccum do all wavelengths of light and other electromagnetic waves travel at the same speed, c = 3 x 10 ^8 m/s 18

Different frequencies (colours) of light actually refract at different angles. This is called dispersion and is especially apparent when white light is passed through a prism.

 A constant associated with a specific medium i.e. plastic, air, water  The amount by which a transparent medium decreases the speed of light  The larger the number, the more the medium decreases the speed of light  Equal to the ratio of the speed of light in a vacuum to the speed of light in the medium at hand (unitless) 21

 The refractive index of a medium is determined by comparing the speed of light in the medium with the speed of light in a vacuum index of refraction of material = speed of light in vacuum speed of light in medium 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 because both m/s speeds cancel out.

23 MaterialIndex of Refraction Vacuum Air Ice1.31 Water1.33 Sugar solution(30%)1.38 Sugar solution (80%)1.49 Typical crown glass1.52 Sodium chloride1.54 Sapphire1.77 Diamond2.417 Oil, Safflower1.466 Oil, vegetable (50° C)1.47 Milk1.35 Glass, Pyrex1.474 Plexiglas1.488

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 = 1.52 x 10 8 m/s n = ? n = 3.00 x 10 8 m/s 1.52 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.

Given: c = c n= 2.42 v = ? v= c/n = 3.00 x 10 8 m/s n V = 1.24 x 10 8 m/s Therefore, the speed of light in diamond is 1.24 x 10 8 m/s The index of refraction in diamond is n = Determine the speed of light in diamond.

 Purpose: How does the angle of refraction and speed of light vary in different media?  Complete the lab sheet and hand in by the end of class! 27