Reflection and Refraction

Transcription

1 Reflection and Refraction 1) Students will be able to state the law of reflection. 2) Students will be able to describe refraction and use Snell's law. 1

2 Teachers' notes Subject Topic Title Grade(s) Cross curricular link(s) Prior knowledge Physics 30 topic title 12 curr. know. Intended learning outcome(s) 2

3 Lesson notes 3

4 Reflection Light travels in straight lines when travelling through a uniform medium. One way that light can interact with matter is to reflect (or bounce off). 4

5 Law of Reflection: the angle of reflection is equal to the angle of incidence Normal line (N): a line perpendicular to the surface Incident ray Reflected ray θ i θ r θ i = angle of incidence θ r = angle of reflection 5

6 A polemescope (or jealousy glass) is a modified telescope fitted with a diagonal mirror to view sideways. They were made to look like an opera (prospect) glass, a low power telescope popular with theatregoers wishing to see the performance on the distant stage more clearly. Used by the gentry from the 18th century, the jealousy glass was employed to spy upon the audience while appearing to be looking ahead at the stage. 6

7 Light travels in straight lines in a uniform medium (or until it hits something). What happens when light moves from one medium to another? Let's see what happens when light enters a glass block. 7

8 Refraction Refraction is the change in direction and wavelength of a wave due to a change in speed. 8

9 Light moving from air to water: Normal air: less dense medium water: more dense medium, light slows down Light bends towards the normal as it enters the more dense medium. 9

10 Light moving from water to air: water: more dense medium Normal air: less dense medium, light speeds up Light bends away from the normal as it enters the less dense medium. 10

11 Snell's Law sin θ 1 = n 2 sin θ 2 n 1 speed of light in the medium n is the refractive index of a material. It is a measure of how fast light travels in the material when compared to c in a vacuum. i.e. n = c v n vacuum = 1.00 n water = 1.33 n crown glass = x 10 8 m/s 11

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13 Practice Problems, p. 668 #1 4 13

14 Snell's law, continued... What happens to the frequency, wavelength, and speed of light as it changes media? 14

15 As light enters a medium that has a higher index of refraction: By c = fλ: Slower medium. *Frequency stays constant! 15

16 As light enters a medium that has a lower index of refraction: Slower medium. By c = fλ: *Frequency stays constant! 16

17 New and improved Snell's Law! sin θ 1 = n 2 = v 1 = λ 1 sin θ 2 n 1 v 2 λ 2 17

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19 p. 670 #1 3 19

20 Which way does a light ray refract as it speeds up? What would happen as the angle of incidence increases? 20

21 Total internal reflection: process in which all of the light is reflected back into the original medium because light can't refract beyond a maximum angle of 90 total internal reflection occurs when a minimum angle (the critical angle) is met 21

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24 p. 673 n quartz =

25 Applications of total internal reflection: Optical fibre (see p. 673) 25

26 Binocular prisms: 26

27 Practice questions: p. 673 #1 27

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30 Mirages: 30

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36 How might these mirages be produced? 36

37 How did those blood thirsty Vikings find Greenland? 37

38 Dispersion: separation of white light into its components Red refracts rotten! Blue bends best! 38

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41 Double Rainbow 41

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43 p. 683 #1 2,5,7,8 11,14 43

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48 Attachments carjumps[1].dir favicon[1].ico