7/24/2019 Refraction&TIR

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Refraction and Total Internal Reflection

Aim:  To determine how light refracts when it passes from one medium to another.

Method:

1. Write the Heading, Aim, and the word  Results on a fresh page of your book.

2. Set up the lightbo to produce a single light ray.

!. "lace your page under the light ray so that you will be able to trace the light as it passes from the cur#ed side of the transparent semi$circle, through the centre pointof the flat side and out into air again.

Q1 Why is there no refraction at the curved side of the block?

%. &n pencil, trace the light rays before and after refraction for an angle of incidence of 

a' appro. 2( degrees,

 b' appro. !( degrees,

c' appro. %( degrees.

 )*T+ there will also be some reflected light. &ndicate this with a dottedline on your diagrams.

Q2 What happens to the angle of refraction as the angle of incidence increases?

Q3 What happens to the amount of reflected light?

. -sing a protractor, measure the angles between the light going in the incident ray'and the light going from the block the refracted ray' back into the air. /ememberthe angle is measured from the normal, not the block surface.

0. Tabulate your results.

. Arrange the light ray so that the angle of refraction is ( degreesie. it 3ust skims the edge of the block'. Trace the light path andmeasure this critical angle of incidence.

Q What is the critical angle of incidence for light passing from glass to air?

4. Arrange the light ray so that the angle of incidence is greater than the criticalangle. Trace the path of the light now.

Q! What happens to the light "hen the angle of incidence is greater than thecritical angle?

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Q# $se %nell&s 'a" n1 sin θ1   = n2 sin θ2

to calculate the (e)pected& critical angle*

ie use: ng sin θi = na sin θc  where ng = 1.5 and  ng = 1.0

+onclusions:

1 When light goes from air into glass or water, it bends ................ the normal,

 ie i*****r

2. When light goes from glass or water into air, it bends ............... the normal,

ie i r 

!. 5or light going from air into glass, sin i 6 sin r 7 ...........see pre#ious prac results if you can8t remember this'.

%. When light goes from glass into air, some is.............. bent' and some is...............

. As the angle of incidence is increased, more light is ......................... and the angleof refraction ...................

0. &f the angle of incidence is large enough, all the light is ...................... back andnone is ..................... This is called T*TA9 &)T+/)A9 /+59+:T&*).

The angle of incidence when this occurs is called the ...................... angle andis ..... degrees for light passing from glass to air.

,)tension Questions:

Q- With the aid of a diagram. e)plain ho" total internal reflection can cause usto (see& mirages eg on roads. desert and over ice* tet ref. pp. !4$!'

Q/ 0o" must an optical fibre be designed so that light can be shone in one end

of the glass and not leave until the opposite end is reached. even if the fibre isbent round corners* 'ist t"o uses of optical fibres* tet ref. p. %('