Refraction 1 What is Refraction The bending or

Refraction 1

What is Refraction? � The bending or change in direction of light as it passes from one substance (medium) to another substance (medium) of differing density 2

Why does light bend? Refraction happens because the light slows down in the new material (the part of the beam that arrives first slows down first) 3

Rules of Refraction � Speed of light changes depending on the medium through which it is travelling � The angle of refraction is the angle between the refracted ray and the normal � Light bends toward the normal when the speed of light in the second medium is less than the speed of light in the first medium � Light bends away from the normal when the speed of light in the second medium is greater than the speed of light in the first medium 4

In each diagram, draw the "missing" ray in order to appropriately show that the direction of bending is towards or away from the normal. Light travels faster in medium 2 Light travels slower in medium 2 Light travels fastest in medium 1 5

Basic Properties of Refraction q. When a ray of light enters a medium where its speed decreases, it is bent toward the normal. q. When a ray of light enters a medium where its speed increases, it is bent away from the normal q. There is no change in direction if there is no change in the index refraction. The greater the change in index of refraction, the greater the change in direction. q. If a ray of light goes from one medium to another along the normal, it is not refracted, regardless of the index of refraction 6

The Index of Refraction The ratio of the speed of light in a vacuum (c) to the speed of light in a medium (v) is called the index of refraction and is represented by the letter n. This is a physical property of the substance (like melting and boiling point) c = speed of light in a vacuum (3. 00 x 108 m/s) v = speed of light in the material 7

Your Turn: Sample Problem#1 What is the index of refraction of a liquid in which the light travels at 2. 04 x 108 m/s? Answer: 8

The Refraction of Light Here are some typical indices of refraction: 9

Snell’s Law The ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant(for the same medium). θi = angle of incidence θr = angle of refraction 10

We can now write the angle of refraction in terms of the index of refraction: Note: the incident ray and the refracted ray are on opposite sides of the normal 11

Snell’s Law - Practice If light passing from water to glass has an angle of refraction of 32°, find the angle of incidence. (nglass = 2. 42 and nwater = 1. 33) n 1 = 1. 33 n 2 = 2. 42 Θ 2= 32° θ 1 = ? n 1 sin(θ 1) = n 2 sin(θ 2) n 1 sin(θ 1) = (2. 42)sin 32 1. 33 sin(θ 1) = 0. 9642 θ 1 = sin-1(0. 9642) θ 1 = 75° The angle of incidence is 75° 12

Snell’s Law - Practice Calculate the angle of refraction in the diagram to the right. nair = 1. 00; nwater = 1. 33 normal 13

Snell’s Law - Practice Calculate the angle of refraction in the diagram to the right. nair = 1. 00; nglass = 1. 52 normal 14

REFRACTION 1. 2. 3. 4. 5. 6. 7. 8. OF LIGHT PROBLEMS The speed of light in glass is 2. 0 x 108 m/s. Calculate the index of refraction for the glass. If light passing from water to glass has an angle of refraction of 25°, find the angle of incidence. (nglass = 1. 46 and nwater = 1. 33) The index of refraction for ethanol is 1. 37. Calculate the speed of light in ethanol. The angle of incidence in diamond is 20°. What is the angle of refraction in air? The speed of light in leaded glass is 1. 66 x 108 m/s. That is the index of refraction for this type of glass? The speed of light through a material is 1. 24 x 108 m/s. What is the material? Light travels from air (n=1. 00) into an optical fiber with an index of refraction of 1. 44. If the angle of incidence on the end of the fiber is 22 o, what is the angle of refraction inside the fiber? What is the speed of light through alcohol? 15

Phenomenon Related to Refraction Summarize the following phenomenon using Internet research Apparent Depth: 16

Phenomenon Related to Refraction The Flattened Sun: 17

Phenomenon Related to Refraction Mirages: 18

Phenomenon Related to Refraction The Rainbow: 19

The Bent Spoon • the spoon looks broken in a glass of water • the light rays bend as they go from the air into the water in the glass • the pattern of the light rays gets distorted due to refraction. 20