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Today • • Questions from homework Quiz Refraction Total Internal Reflection

Monday Tuesday Wednesday 25 Light as EM radiation 26 Sources of Light Additive and subtractive colour 27 Additive and subtractive colour 2 Plane mirrors Concave mirrors 3 Convex mirrors Curved mirror equation 4 Strike day 9 Refraction activity Part If 10 Refraction activity Part II 16 The eye, applications of lenses 17 Review activity Thursday Friday 28 Ray theory Light and shadow Reflection Types Plane mirrors 5 Curved mirror equations 29 P. A. Day 11 Lab write up day 12 Lens diagram— concave 13 Lens diagrams— convex 18 TEST 19 Climate change 20 Carnival 6 Refraction—total internal reflection Quiz

Demo: broken spoon Demo: disappearing/reappearing coin • Use POE (Predict, Observe, Explain) • Try to draw ray path diagrams as part of your explanation

Useful Definitions: Medium • A material (substance) that is undergoing a process (light is passing through it in this case) Media • Plural of medium, sometimes these substances can be stacked Reflection • Energy or waves (light in this case) “bouncing” off a surface (draw a picture!) Refraction • Energy or waves (light in this case) that changes direction due to differences in the speed it can travel through a medium (draw a picture!) Index of Refraction • The relative differences in speed that energy or waves (light) can travel between different media

Speed of Light: • Light travels at 3. 0 x 108 m/s in a vacuum (in “space”) • Light travels at different speeds in different media Index of Refraction

Index of Refraction: Example The speed of light in a sample of glass is 1. 91 × 108 m/s. The speed of light in a vacuum is 3. 00 × 108 m/s. What is the refractive index of this glass? What is the speed of light in water given that water has a refractive index of 1. 33?

How does refraction work? As the light waves (or any waves) approach an interface, some parts of the wave enter the medium at different times, and get dragged (imagine it like a car approaching the gravel shoulder of the road at an angle and how it slows down as it drives across the gravel).

How does refraction work? As the light waves (or any waves) approach an interface, some parts of the wave enter the medium at different times, and get dragged (imagine it like a car approaching the gravel shoulder of the road at an angle and how it slows down as it drives across the gravel). θi Fast medium Slow medium θr θr is smaller than θi when light travels from a fast medium to a slow medium θr is larger than θi when light travels from a slow medium to a fast medium Fast medium

Critical Angle and Total Internal Reflection Critical angle • Incident angle beyond which light does not pass out of the medium but is “trapped” inside—called total internal reflection • The light looks like it shoots along the interface between the media • Happens only when energy or waves (light in this case) pass from a slow medium to a fast one (eg. glass to air)

Snell’s Law: The relationship between incident and refracted angles and the index of refraction Observed since humans tried to spear fish, quantified in early 1600 s to allow us to calculate refracted angle (measured from the normal). n 1 sinθ 1 = n 2 sinθ 2 n 1 = index of refraction (originating medium) n 2 = index of refraction (end medium) θ 1 = incidence angle (originating medium) θ 2 = refraction angle (end medium)

Snell’s Law—Examples When light passes from air into water at an angle of 60° from the normal, what is the angle of refraction? 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°, and the angle of refraction is 27°. What is the index of refraction of cubic zirconia?

Homework • Study sheet • practice sheet(s) • Bring rulers (maybe even coloured pencils!)