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Physical Science –
Part 1 : Theoretical Research Of
Refraction And Snell’s Law
Dylan O’ Bryan
Grade 11K3
2018
1

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Table Of Contents
Cover Page Page 1
Table Of Contents Page 2
Theoretical Research – Questions and Answers Page 3 – 8
Illustrations Page 9 – 10
Bibliography Page 11
Appendix and Plagiarism Report Page 12 – 13

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Theoretical Research –
Questions and Answers
1.1 State the law of reflection.
The incident ray, the reflected ray and the normal, are all in the same plane. The angle of
incidence is equal to the angle of reflection. (Merriam-Webster, Incorporated, 2018)
1.2 Discuss the speed of light in a vacuum and describe changes in the speed of light as it
move from one medium to another.
Light does not need a medium to travel, but can be affected by it. In a vacuum; light
travels at a speed of 3×10?m.s¯¹, but when light comes into contact with a medium, the
speed of light changes according to the type of medium.
1.3 Define refraction.
Refraction is the bending of light as it moves from one medium to another medium with a
different optical density. (The Editors of Encyclopaedia Britannica, 1998)
1.4 Discuss the term refractive index and give a mathematical equation for it.
The speed of light changes as it comes in contact with a medium, causing it to bend,
depending on the optical density. For example; the speed of light through a diamond is
1,34×10?m.s¯¹, and through glass it is 2×10?m.s¯¹. A diamond has a greater optical density,
therefore bending the light closer to the normal.

Refractive index = Speed of light in air
Speed of light in medium

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Reflection: The return of light or sound waves from a surface.
Refraction: Is the change in direction of wave propagation due to a change in its transmission medium.

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Theoretical Research –
Questions and Answers
1.5 a. What is optical density?
Optical density is a measure of the speed of light through a medium.
(Reference.comScience, n.d.)
1.5 b. Compare the optical density of glass and water.
Glass is 2,0×10?
Water is 2,26×10?
Glass has a greater optical density than water.
1.6 Give the refractive index of glass and perspex and discuss how it is related to the optical
density of each substance.
Glass is 1,52
Perspex is 1,50
The refractive index plays a role as the speed of light in each medium.

v = c v = c
n n

v = 3×10? v = 3×10?
1,52 1,50

v = 197×10?m.s¯¹ v = 200×10?m.s¯¹
:. Light trends faster in perspex than in glass.

4
(Doc Scienta Textbook, Ronel
Bernado and others)

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Theoretical Research –
Questions and Answers
1.7 Explain that refraction is a change of wave speed in different media, while the frequency
remains constant.
Light travels at 3×10?m.s¯¹ in a vacuum and 200×10?m.s¯¹ in perspex. Therefore the speed
of light can differ from one medium to another. This does not affect the wave length but
rather the speed at which it travels.
1.8 Study the following ray diagram and give the definition for each of the following:
a. The Normal
The normal is an imaginary line at 90° to the surface of the mirror. The normal provides a
straight line from which to measure the angles.
b. The angle of incidence
The angle of incidence (?i) is the angle between the incident ray on the normal.
c. The angle of refraction
The angle of reflection (?r) is the angle between the reflected ray and the normal.

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(Doc Scienta Textbook, Ronel
Bernado and others). Refer to
Appendix B

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Theoretical Research –
Questions and Answers
1.9 State Snell’s law.
Snell’s law states that if light strikes a right angled glass prism at an angle, refraction will
take place. If the values for the angle of refraction ?r for different incident angles ?i are
measured, the following results are found. . (Merriam-Webster, Incorporated, 2018) (Refer
to Appendix B)

1.10 Explain the concept of critical angle.
When you stand in a swimming pool, you can see the feet of the person in front of you, but
as you move away from the person, you can no longer see the persons body in the water,
only above the water. The reason for this is the total internal reflection of water moves into
the air. The speed of the light increases and it bends away from the normal. The further
you move, the angle of the incidence gradually increases until the refracted ray runs along
the surface between the two mediums. At that point, the angle of refraction is 90° and the
angle of incidence is known as the critical angle. (Molecular Expressions, 2003),

?i 10° 20° 30° 40° 50° 60° 70°
?r 6,4 13 19 25 30,5 35 38,3
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Theoretical Research –
Questions and Answers
1.11 List the conditions required for total internal reflection.
The incident ray must move from optically more dense medium towards an
optically less dense medium. The angle of incidence must be greater than the
critical angle of that medium. (Refer to Appendix B)
1.12 Define optical fibres, endoscopes and telecommunication.
Optical fibres are thin, flexible and made from glass which allows the light to
pass through them. Each fibre in a bundle carries the light from one piece of a
picture. Together the bundle carries the whole picture. Endoscopes are used by
doctors to examine the inside of a patient. Telecommunication – copper wire is
being replaced by fibre opties, because optical fibre have many advantages over
copper wire, i.e. optical fibres do not have a resale value, this eliminates theft.

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(Doc Scienta Textbook, Ronel
Bernado and others)
Endoscopes: A procedure in which an instrument is introduced into the body to give a view of its internal
parts.

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Theoretical Research –
Questions and Answers
1.13 Tabulate the advantages and disadvantages of the use of optical fibres.

1.14 Discuss the effect of the usage of optical fibres on the environment.
Sea cables have been used since the 19th century. Environmental problems
associated with the placement are only recent. The biggest reason for the
increased awareness is due to the increased development of offshore wind farms
and the related increase of the use of submarine power cables.
Advantages Disadvantages
It is lighter and thinner than copper wire. Optic fibres are made out of glass, therefore
they are more fragile.
It can transfer more data simultaneously than
copper wire.
It is more expensive than copper wire.
Greater security. Extra optical components like EDFA are required
to transfer information across greater distances.
It is easier to lay cables.
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(Doc Scienta Textbook, Ronel
Bernado and others)

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Illustrations
Law Of Reflection
9

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Illustrations
Snell’s Law
10

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Bibliography
1.https://www.britannica.com/science/Snells-law
2.http://www.physicsclassroom.com/class/refrn/Lesson-2/Snell-s-Law
3.https://courses.lumenlearning.com/physics/chapter/25-2-the-law-of-reflection/
4.http://www.animations.physics.unsw.edu.au/jw/light/Snells_law_and_refraction.h
tm
5.https://byjus.com/snells-law-formula
6.http://farside.ph.utexas.edu/teaching/302l/lectures/node128.html
7.http://www.loretobalbriggan.ie/physics/Experiment%20worksheets/Snell%27s%2
0law.PDF
8.http://www.dartmouth.edu/~physics/labs/descriptions/snells.law.lenses/snells.len
s.writeup.pdf
9.http://www.math.ubc.ca/~cass/courses/m309-01a/chu/Fundamentals/snell.htm
10.https://www.cis.rit.edu/class/simg232/lab2-dispersion.pdf
11.http://www.loretobalbriggan.ie/physics/Experiment%20worksheets/Snell%27s%2
0law.PDF
12.http://hyperphysics.phy-astr.gsu.edu/hbase/index.html
13.https://www.merriam-webster.com/dictionary/law%20of%20reflection

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Appendix A – Information
Collection
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•Hyper Physics (Department of Physics and Astronomy)
•Snells Law (Merriam-Webster)
•Refraction (The Physics Hypertextbook)

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Appendix B –
Pictures for visual impact
•(Various websites and
Google Images)
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Total Internal Reflection