Law of Refraction

9 Physical SciencesLight III

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Note

Important Points

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Refraction

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A DVD disc and a bottle of water have been provided to you.

Place some water on the disc and observe. DVD Activity

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Water Beads

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The light beam is bent: between the air and the liquid; between the liquid and the glass.

As the light crosses the boundary between two different mediums, it is bent, producing a distorted image.

The bending of light is called refraction.

Refraction

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A material which light passes through, such as glass or air, is known as a medium.

When light passes through air, it travels at about 300,000,000 m/s (about the same as it does in a vacuum).

Refraction

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A measurement used to determine how easily light is bent in a different medium. Refractive indexThe higher the value of the refractive index, the more difficult it is for light to bend.

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MediumRefractive Index, nSpeed of light, v (m s-1)Air1.003 x 108 = cWater1.332.26 x 108Diamond 2.421.24 x 108

As the refractive index increases, the speed of light within the medium decreases. Refractive index

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When the car moves into a different road surface, it changes speed as it enters from the road to the sand.Here, the cars right wheel will slow down first as it hits the sand, causing the car to veer right.

Analogy

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In this situation, when the car is driven at a right angle, the car will not change its angle.

However, the speed of the car changes because the nature of the road surface determines the speed. Analogy

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The incident ray (i) and refracted ray (r) are on the opposite sides of the normal at the point of incidence, and all three lie on the same plane.

irNormal linePoint of incidenceLaw of Refraction

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The mediums involved in the law of refraction will only be air/water or air/another medium.

irNormal linePoint of incidenceLaw of Refraction

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normalairglass

incidentrayrefracted rayangle of incidenceangle of refraction More dense medium

The ray of light is refracted or bent towards the normal from the air into the glass.

Note that the angle of refraction, r is smaller than the angle of incidence, i.

r < i

This means that glass is more dense than air.

Light is bent towards the normal when it enters a medium of a higher refractive index.

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normalairglass

incidentrayrefracted rayangle of incidenceangle of refraction Less dense medium

The ray of light is refracted or bent away from the normal from the air into the glass.

Note that the angle of refraction, r is larger than the angle of incidence, i.

r > i

This means that air is less dense than air.

Light is bent away from the normal when it enters a medium of a lower refractive index.

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In the diagram below, label the following terms:

a) ray of incidenceb) ray of refractionc) angle of incidenced) angle of refraction

What can you conclude about the mediums?

Example 1

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In the diagram below, label the following terms:

a) ray of incidenceb) ray of refractionc) angle of incidenced) angle of refraction

What can you conclude about the mediums?

Example 1 answersb c a d The glass medium is more dense than the air medium. Glass has a higher index of refraction than air.

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Sketch a ray diagram for the following angles. Example 2i = 30 r = 65i = 90 r = 90

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Example 2 answersi = 30 r = 65i = 90 r = 90Sketch a ray diagram for the following angles.

30

65

All angles are draw from the normal.

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The chest appears to be at a shallower water than its original position. This causes a depth illusion to the viewer on the boat. Depth illusion

Light reflected off the chest is bent away from the normal from water to air.

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Image of Refraction

When you look at the refracted light, your retina processes the light in a straight line. Hence, this makes the chest appear to be closer to the water.

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Archer Fishs Aim

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