sec 2 light - refraction_handout

7/30/2019 Sec 2 Light - Refraction_handout

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Refraction of light


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Objectives

describe some effects and consequences ofrefraction

explain the difference between reflection andrefraction

recall and use the terms for refraction, includingnormal, angle of incidence and angle of refraction.

recall and apply the relationship sin i/ sin r=constant to new situations or to solve relatedproblems

define refractive indexof a medium in terms of theratio of speed of light in vacuum and in themedium


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Refraction of light

Light source

Glass block

from: http://www.physics.brown.edu/physics/demopages/Demo/optics/demo/6a4210.htm


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What is Refraction?

Refraction is

This is due to a

Medium: the substance that light passes

through

E.g. air, water, glass, plastic, diamond O measure of the

material to enable transmission of light

The more optical the medium, the

light travels


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When does refraction occur?

Refraction occurs when

1. there is a in speed of the light

wave, and

2. the light wave approaches the boundary atother than to the

boundary.


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Ray diagram for refraction

airglass

Actual snapshotRay diagram


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Refraction vs Reflection

Incident ray

water

air


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Law of Refraction

Also known as Snells Law

Willebrord Snell (1580 1626)

from: http://www.iesfelanitx.org/departaments/fisica-quimica/retrats/snell.jpg


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Refractive index

Refractive index, n, of a medium is

.

Refractive index affects how much light bends.


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Refractive index

The ratio is constant, however it

differs for different medium.

For the special case oflight passing from a

vacuum (or in practice, air)into a givenmedium, the

.

vacuum

medium

i

r


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normal

Incident ray

water

air

When light travels from an optically less dense

to a denser medium, light bends towards the

normal


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normal

incident ray

water

air

iis smaller than r

When light travels from an optically denser to

a less dense medium, light bends away from

the normal


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Example 1

The diagram shows a ray of light incident on thesurface of a liquid and its subsequent path. What

is the refractive index of the liquid?

air

liquid

59

40


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Example 2

air

crown glass

i

If light is incident upon crown glass (n = 1.52) at an angleas shown, what is the angle of refraction? Complete the

drawing of the ray diagram.


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Reversibility of light

The principle of reversibility states that light

will follow exactly the same path if its

direction of travel is reversed.

air

crown glass

40air

crown glass

25


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Example 3

A ray of light emerges from water (n= 1.33) to air.Calculate the angle of refraction, r.

air

water

r

35


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Effects of Refraction

Apparent Depth

Distortion of objects

Multiple images


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Apparent depth

Due to refraction, the depth of water looks

shallower.

This perceived depth is called apparent depth.


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You can use apparent depth to calculate the

refractive index of a medium.


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Due to refraction, the stick appears bent

underwater.


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Multiple images

How many

goldfish are there?


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Multiple images

Front viewSide view

sec 2 light - refraction_handout

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