Refraction is the change in speed of a wave due to the wave entering a different medium. light travels at different speeds in different media

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Amelia Shavonne Ferguson
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1 Refraction

2 Refraction is the change in speed of a wave due to the wave entering a different medium light travels at different speeds in different media this causes light to bend as it passes from one substance to another if the angle of incidence is greater than zero degrees

4 as light enters a different medium, the wavelength and speed will change, but the frequency will remain the same

5 the speed of a wave is controlled by the properties of the medium, but the wave frequency is determined by the wave source the change in speed occurs at the boundary

6 Light will bend towards the normal if angle of incidence > 0

7 Waves will bend away from the normal if the speed increases.

8 Refraction & Wave Theory Refraction could be explained by both theories

9 Refraction & Wave Theory Particle theory predicted the speed would increase in more dense material

$Refraction & Wave Theory Wave theory predicted the speed would decrease in more$

10 Refraction & Wave Theory Wave theory predicted the speed would decrease in more dense material Experiments verified light speed was less in more dense material

$Refraction of light through a prism the beam bends toward the$

11 Refraction of light through a prism the beam bends toward the normal as it enters and away from the normal as it leaves the glass

$the amount of refraction and the change in$

12 Snell s Law mathematical relationship between the amount of refraction and the change in speed

13 index of refraction (n) is a measure of how much waves will refract or change speed when they enter another medium n has no units n = (exact value) for a vacuum all other values of n 1.000

14 the value of n depends on the wavelength n decreases as increases Values in medium 1 sinθ 1 v 1 1 n 2 sinθ 2 v 2 2 n 1 Values in medium 2

15 Example A beam of light traveling in air enters a piece of glass. The angle of incidence is 72.0 o and the angle of refraction is 39.3 o. Determine the refractive index of the glass.

16 Solution 1 = 72.0 o n 1 = = 39.3 o sinθ 1 sinθ 2 n 2 n 1 n 2 =? n 2 = 1.50

17 Example A beam of light in salt water (n = 1.43) enters a piece of plastic (n = 1. 22). If the angle of incidence is 34.0 o, determine the angle of refraction. sinθ 1 sinθ 2 sin 34.0 sin 2 n 2 n

18 Refraction effects the amount of light reflecting from the boundary between 2 transparent media depends on the difference in n values Anti-reflective coating on lenses reduces glare

19 objects appear to be shallower than they really are

$red light refracted into Earth's shadow by the$

21 Total Lunar Eclipse The red colour of the moon is due to red light refracted into Earth's shadow by the atmosphere

22 Practice P 668: 1, 2 (See the table on top of P 667) P 670: #1 a, 2, 3

23 Dispersion Dispersion is the separation of different wavelengths because of different refractive indices

24 Dispersion Newton showed that white light was composed of the colours of the spectrum and could be recombined to form white light again

25 Short waves are refracted more than long waves n violet > n red

30 When light passes from a medium with a high n to a medium with a low n, the light bends away from the normal

$Total Internal Reflection As the incident angle increases, the angle of refraction$

31 Total Internal Reflection As the incident angle increases, the angle of refraction increases When the angle of refraction = 90 o, the angle of incidence is called the critical angle

$When the angle of refraction > 90 o, the$

32 When the angle of refraction > 90 o, the ray will be reflected into the original medium

35 The atmosphere blurs the light it lets through. The blurring is caused by varying density and continual motion of air. HST has a mirror 15 times smaller than large Earthbound telescopes, it can still resolve finer details.

36 STS Fibre optics, single lens reflex (SLR) cameras use TIR to transmit data and bend light Light reflects off the interior surface of the cable with little loss Allows multiple signals to be used in a single cable

37 Fibre-optic cable

38 Refraction of radio waves

39 Example Determine the critical angle for a water (n = 1.33) & diamond (n= 2.42) interface. (critical angle of incidence causes 90.0 o of refraction)

40 Solution sin 1 sin 2 n 2 n 1 sin 1 sin

41 Example A beam of light traveling in water (n = 1.33) strikes the boundary with air (n = 1.00). If the angle of incidence is 56.0 o, determine the angle of refraction.

42 Angle in water Angle in air sin 2 = 1.33 sin 56.0 o = Solution sin sin n 1 n sin sin n 2 n sinsin sin sin doesn t exist (sine of can t be larger than 1) so refraction doesn t occur, the light is reflected off the water-air boundary at 56.0 o.

43 THINK! Calculate the critical angles for the following interfaces and relate the angles to the ratio n 2 : (see p 667) n 1 a. Ice & air b. Ethanol and zircon c. Diamond and air sin sin sin sin 90 o n 1 2 n 2 1 n 1 2 n 1

44 Solution a. Ice air critical = 49.8 o n 2 n 1 = b. Ethanol zircon critical = 45.5 o n 2 n 1 = c. Diamond air critical = 24.4 o n 2 n 1 = As n 2 n 1 decreases, the value of critical decreases

45 Rainbows Total internal reflection occurs on the far side of the rain drop Violet light emerges at 40 o from its original path

46 Each drop forms a complete spectrum, an observer will only see a certain colour from each drop

$prism, refracting different colors of light on slightly different$

48 these effects arise when the Earth's atmosphere acts like a prism, refracting different colors of light on slightly different paths.

49 Dispersion occurs in gems

53 Practice P 683: 11, 12, 13, 14

Science 8 Unit 2 Pack:

Science 8 Unit 2 Pack: Name Page 0 Section 4.1 : The Properties of Waves Pages By the end of section 4.1 you should be able to understand the following: Waves are disturbances that transmit energy from