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.

Refraction

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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

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Why does light bend?Refraction happens because the light

slows down in the new material

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(the part of the beam that arrives first slows down first)

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

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In each diagram, draw the "missing" ray in order to appropriately show that the direction of bending is towards or away from the normal.

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Light travels faster in medium 2

Light travels slower in medium 2

Light travels fastest in medium 1

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Basic Properties of RefractionWhen a ray of light enters a medium where its

speed decreases, it is bent toward the normal.

When a ray of light enters a medium where its speed increases, it is bent away from the normal

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.

If a ray of light goes from one medium to another along the normal, it is not refracted, regardless of the index of refraction

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.

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v

cn 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

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:

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47.1/1004.2

/1000.38

8

smx

smx

v

cn

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The Refraction of Light

Here are some typical indices of refraction:

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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).

nr

i

sin

sin θi = angle of incidenceθr = angle of refraction

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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

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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)

n1 = 1.33n2 = 2.42Θ2= 32°θ1 = ?

Snell’s Law - Practice

n1sin(θ1) = n2sin(θ2)sin(θ1) = n2sin(θ2)

n1

sin(θ1) = (2.42)sin321.33

sin(θ1) = 0.9642θ1 = sin-1(0.9642)θ1 = 75°

The angle of incidence is 75°

Calculate the angle ofrefraction in the

diagram to the right.nair = 1.00; nwater =

1.33

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001 416.40)651146.0(sin

651146.033.1

60sin00.1sinsin

sinsin

r

o

water

iairr

rwateriair

x

n

n

nn

normal

Snell’s Law - Practice

Calculate the angle ofrefraction in the

diagram to the right.nair = 1.00; nglass =

1.52

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001 357.34)569753.0(sin

569753.052.1

60sin00.1sinsin

sinsin

r

o

glass

iairr

rglassiair

x

n

n

nn

normal

Snell’s Law - Practice

REFRACTION OF LIGHT PROBLEMS

1. The speed of light in glass is 2.0 x 108 m/s. Calculate the index of refraction for the glass.

2. 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)

3. The index of refraction for ethanol is 1.37. Calculate the speed of light in ethanol.

4. The angle of incidence in diamond is 20°. What is the angle of refraction in air?

5. 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?

6. The speed of light through a material is 1.24 x 108 m/s. What is the material?

7. 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 22o, what is the angle of refraction inside the fiber? 

8. What is the speed of light through alcohol?

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Phenomenon Related to RefractionSummarize the following phenomenon using Internet research

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Apparent Depth:

Phenomenon Related to Refraction

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The Flattened Sun:

Phenomenon Related to Refraction

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Mirages:

Phenomenon Related to Refraction

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The Rainbow:

The Bent Spoon

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• 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.