Refracon. Refracon The spoon in the glass photo can be translated into a ray diagram.

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1 The of Light Learning Goals: to understand why light refracts when travelling through different media to calculate the index of refraction to use the index of refraction to calculate the speed of light through a certain medium to predict the change in direction of a ray of light travelling through different media is the bending of light when it crosses a boundary between two substances. Any substance light rays travel through is called a medium or media (plural). In the photo below the two media are air and water. The spoon in the glass photo can be translated into a ray diagram. Air Medium 1 Normal Incident Ray Angle of Incidence Water Medium 2 Refracted Ray Angle of 1

2 What Causes? Light refracts because light travels at different speeds in different media. The Speed of Light Light travels at almost 300 million m/s or 3.0 x 10 8 m/s.. through a vacuum. Moving at this speed light could travel seven times around the Earth in one second. However, it is impossible for light to travel at top speed when particles get in the way. The Index of Index of the amount by which a transparent medium decreases the speed of light. The larger the refracve index, the more the medium decreases the speed of light. Some indexes of refracon vacuum: n=1.00 air: n= water: n=1.33 sapphire: n= 1.77 diamond: n=

3 The Index of index of refracon of material = speed of light in a vacuum speed of light in a medium n = c v OR Since units cancel, a refracve index value does not have any units. The Index of The speed of light in a sample of glass is 1.91 x 10 8 m/s. The speed of light in a vacuum is 3.00 x 10 8 m/s. What is the refracve index of this glass? 1.57 The Index of What is the speed of light in water given that water has a refracve index of 1.33? 2.26 X 10 8 m/s The angle of the refracted light rays are usually measured from the normal, drawn at 90 O to the surface where the light ray crossed between the two media. When light travels from air, with a low refractive index, into water, with a higher refractive index, it bends toward the normal. When light travels from a denser (higher refractive index) into less optically dense (lower refractive index) medium, it bends away from the normal. 3

4 For Example: In the figure below you see a car travelling along a smooth pavement and entering an area of muddy surface. Smooth Pavement For Example: When the res enter the mud, they move more slowly than they did on the pavement. As a result, the path of the travelling car bends toward the line in the diagram. Smooth Pavement Muddy Surface Muddy Surface For Example: In the below diagram the situaon is reversed. The car is travelling along a muddy surface and entering an area of smooth pavement. Muddy Surface For Example: When the res enter the smooth pavement, they move more quickly than they did on the mud. As a result, the path of the travelling car bends away from the line in the diagram. Muddy Surface Smooth Pavement Smooth Pavement 4

5 Dispersion Is the refracon of white light into separate wavelengths or colours. Examples diamond and raindrops. The most common type of dispersion is in the formaon of a rainbow. how is refraction and reflection n= 1.47 n= 2.16 n= 1.47 n= 1.33 similar? both involve a wave hitting a medium both involve changing direction of a wave different? refraction: wave is allowed through reflection: wave cannot go through medium refraction: the wave slows down reflection: the wave stays the same speed 5

6 HANDOUT + pg. 438 #1 3, and #1 3 n 1 sin0 1 = n 2 sin0 2 this salad is yummy this salad is yummy Cole's Law Formula n 1 sin0 1 = n 2 sin0 2 Normal Incident Ray θ 1 Angle of Incidence Indices of refracon of the two media n 1 and n 2 Angle of incidence 0 1 Angle of refracon 0 2 Interface Angle of θ 2 n 1 n 2 Refracted Ray 6

7 When light passes from air into water at an angle of 60 0 from the normal, what is the angle of refracon? In an experiment, a block of cubic zirconia is placed in water. A laser beam is passed from the water through the cubic zirconia. The angle of incidence is 50 0, and the angle of refracon is What is the index of refracon of cubic zirconia? Total Internal Reflecon Total Internal Reflecon Light reflects completely off the inside wall of a denser medium (higher index of refracon) rather than passing through the wall into a less dense medium (lower index of refracon). Example fiber opcs Total Internal Cric al Angle 7

8 TRY THESE.. Pg. 441 # 1 3 Pg. 442 # 1 3 8