What is meant by ' Total Internal Reflection '. The total ... A semi-circular glass
bolock is placed on a sheet of ... Total internal reflection occurs at this layer.
S M K Pahi Bidang sains dan matematik LESSON 5.3 - Total internal reflection
The Critical Angle, c The angle of incidence in an optically more dense medium which results in angle of refraction of 90o in an optically less dense.
LESSON 5.3 TOTAL INTERNAL REFLECTION What is meant by ‘ Total Internal Reflection ‘
Determine the relationship between Refractive index (n) and Critical angle (c)
The total reflection of a beam of light at the interface of one medium and another medium of lower refractive index (optically less dense) , when the angle of incidence to the second medium exceeds a specific critical angle. Ray diagram to show how the Total Internal Reflection happen ?
n = sin i sin r n=
(1) Angle of incidence ,i1 is small. Produces a strong refracted ray and a weak reflected ray.
n=
(2) Angle of incidence is increased as i2. Produces a refracted ray and a reflected ray whose intensity has increased compared to the situation in (1)
1 sin c
Example 1
(3) Angle of incidence is increased to the critical angle, c. The refracted ray travels along the waterair boundary.
The diagram shows a light ray entering in a glass prism. [ Refractive index of glass = 1.51 ]
(4) Angle of incidence , i3 > c. No refraction occurs. All the light is reflected within the water . Total internal reflection occurs. (a) Determine the critical angle of the glass. (b) Draw the ray light after it passes through a point P until the direction of the ray of light unchange.
The conditions for the occurrence of total internal reflection. (1) The light ray must be travel from an optically denser medium to less dense medium. (2) The angle of incidence must be greater than the critical angle.
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S M K Pahi Bidang sains dan matematik LESSON 5.3 - Total internal reflection
Experiment to determine the critical angle of glass.
Solution
A semi-circular glass bolock is placed on a sheet of white paper. The outline of the glass block is traced onto the paper as ABC. The glass block is put aside. A normal ON is drawn. The glass block is placed again on its outline. A ray of light from the ray box is directed to glass block. The angle of incidence is increased until the refracted ray travels along the length of the air- glass boundary ( refraction angle is 90o ). By using a protractor the angle of incidence is measured = c The crtical angle of the glass block = c
Example 2 Figure shows a light ray AO travelling from medium X to the air. [The refractive index of medium X = 2.0 ]
Natural phenomena and Use of Total Internal Reflection. Mirages(fatamorgana)
Draw the ray light after it passes through the point O when (a) θ = 25o (b)θ = 30o (c) θ = 35o Solution
In thetime when the weather is hot , the incidence ray from the sun passes through a dense air layer to a less dense air layer. Finally , the ray of passes through the air layer close to the road surface at an angle of incidence greater than the critical angle. Total internal reflection occurs at this layer. The observer sees the image of the sky on the surface of the road as a pool of water.
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S M K Pahi Bidang sains dan matematik LESSON 5.3 - Total internal reflection
Fibre optics
Prism periscope
The periscope is built using two right –angled prisms made of glass . The crtical angle of the prism is 42o . The angle of incidence is 45o is greater than the critical angle. Total internal reflection occurs. The characteristics of the images are (i) Virtual (ii) Upright (iii) Same size as the object. Advantanges of the prism periscope compared to mirror periscope, (i) The image is brighter (ii) No multiple images is formed (very clear)
The external wall of a fibre optic is less dense than the internal wall. When light rays travel from a denser internal wall to aless dense external walls at an angle that exceeds the critical angle , total internal reflection occurs. The advantages of the fibre optics: (i) Cheap (ii) easily handled (iii) More information can be transmitted
Binocular
A ray light experiences two total internal reflections at each prism. The two prisms is to invert the image (upside down and right-to-left.) But the lenses in the binoculars also invert the image and so the the prisms put it back the right way again. So the final image in binoculars is upright ,not laterally inverted and magnified.
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S M K Pahi Bidang sains dan matematik LESSON 5.3 - Total internal reflection
TUTORIAL 3 1
A ray of red light travelling in glass strikes the glass-air boundry . Some light is reflected and some is refracted. Which diagram shows the paths of the rays?
2 One of the diagram below shows the path of a beam of light that is incident on a water-air surface with angle of incidence greater than the critical angle. Which one is it?
4
Which of the following shows total internal reflection?
5
The diagram shows light ray XO experiencing total internal reflection when travelling from the glass to air.
Which statements about total internal reflection are correct?
3
P - θ is more than the critical angle of glass Q - The speed of light in the glass is higher than in air R - The refractive index of glass is greater than air
Which of the following diagram correctly shows the total internal reflection of ray of light? [ Refractive index of medium X = 1.3 Refractive index of medium Y = 1.5 ]
A B C D
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P and Q P and R Q and R P,Q and R
S M K Pahi Bidang sains dan matematik LESSON 5.3 - Total internal reflection
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The diagram shows a semi-circular plastic block is placed in a liquid.
A C
OB OD
B D
OC OE
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A ray of light incident on one side of a rectangular glass block. If the angle of refraction in the glass block is 40o , which one of the following diagrams best reprents this ray? [ The critical angle of glass is 42o ]
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The diagram shows a light ray, P, directed into a glass block. The critical angle of the glass is 42o. In which direction does the light move from point Q?
Which of the following is correct? A B C D 7
Density of the plastic block is less than density of the liquid Refractive index of the plastic block is less than refractive index of the liquid Critical angle of the plastic block is less than critical of the liquid Angle of incidence is less than critical angle of the liquid
The diagram shows a ray of light passing through medium to medium N.
Which of the following is correct? A B
The angle of reflection is 55o The critical angle of medium M less than
C
Density of medium M less than the density of medium N
35o
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The figure shows a ray of light AO traveling in a liquid strikes the liquid-air boundary. [ The critical angle of the liquid = 45o ]
In which direction does the light move from O ?
5
S M K Pahi Bidang sains dan matematik LESSON 5.3 - Total internal reflection
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The diagram shows a light ray , M, directed into a glass block. The critical angle of the glass is 42o. In which diagram does the light move from point O?
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The figure shows a ray of light is incident in air to the surface of Prism A and B.
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The diagram shows a light ray travelling from air into a plastic block with an angle of incidence ,X. What is the critical angle of the plastic?
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The diagram shows a light ray travelling from air into a glass prism.
Which comparison is correct ? A B C 13
The critical angle is A B C D
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Density of prism A < density of prism B Critical angle of prism A < critical angle of prism B Refractive index of prism A < refractive index of prism B
the smallest angle of incidence in optically more dense medium the smallest angle of incidence in optically less dense medium the greatest angle of incidence in optically more dense medium the greatest angle of incidence in optically less dense medium
What is the critical angle of the glass? A C E
Which of the following shows the correct critical angle , c of the semi- circular glass block ?
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40o 60o 80o
B D
50o 70o
S M K Pahi Bidang sains dan matematik LESSON 5.3 - Total internal reflection
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A C E
18
44.5o 48.8o 54.3o
B D
46.9o 49.2o
The refractive index of plastic block is 13 . 5 What is the value of the cosine of the critical angle of the plastic? A
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21 The diagram shows a cross- section of a fibre optic cable.
The refractive index of water is 1.33. What is the critical angle of the water.
5 12
B
C
13 12
D
E
13 5
Which comparison is correct ? A B C
12 13
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5 13
Density of P < density of Q Density of P >density of Q Density of P = density of Q
The diagram shows a long block of glass over an object O. Light from O reaches the top surface of the glass at X , Y and Z.
The figure shows a ray of light AO traveling in medium X strikes the medium X-air boundary. [ The refractive index of medium X = 1.12 ] (a) What is the name given to the bending of light at X? ………………………………………………… (b) At Z light is ……………. …………… reflected. (c)
In which direction does the light move from O ?
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………………………………………………… (d) Explain why light is reflected as shown at Z?
A OE B OD C OC D OB Which of the following not applies the principle of total internal reflection? A B C D
Give the name of the angle marked R.
…………………………………………………
Prism binocular Mirror periscope Optical fibre Road mirage
………………………………………………… …………………………………………………
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S M K Pahi Bidang sains dan matematik LESSON 5.3 - Total internal reflection
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A ray of light is incident at an angle of 60o at mid-point O of the plane face AB of a semicircular glass block as shown in Figure(a).
ray directed towards O which undergoes total internal reflection at the surface AB.
24 (a)
(i) Calculate the angle of refraction of this ray at O, given that the refractive index of the glass is 1.5. (ii)
(b)
The diagram show a ray of light XOYZ is incident at angle of 600 to an ice block.
Draw the path of this ray from O on Figure(a) and continue its path until it has emerged into the air. (i) Calculate the critical angle for the glass-air boundry.
(ii)
(a) Mark the critical angle of ice with ”c” in the figure above. (b) Determine the value of the critical angle , c.
On Figure(b) below draw the the path of a ray which travels through the glass to O in such way it strikes the surface AB at an angles of incidence equal to the the critical angle and continues the path of this ray after it has struck the surface AB at O.
(c)
Calculate the refractive index of ice.
(d) Explain how the direction of ray of light XO can be changed to ensure the total internal reflection will occur ? (c) On Figure(c) draw the complete path of a ............................................................................. 8
S M K Pahi Bidang sains dan matematik LESSON 5.3 - Total internal reflection
............................................................................. (e) What happen to the critical angle when the ice block is replaced by a substance which has the refractive index 1.8 ? ……………………………………………………… ……………………………………………………… 25
The diagram shows a ray of light XO is incident to a glass prism PQR. [The refractive index of glass is 1.5]
(a) Why is the ray of light XO entering the prism in a straight line? ............................................................................. ............................................................................. (b) Determine the critical angle of the glass prism.
(c)
By using certain calculations, draw the complete path of a ray started from Y until the direction of the path of ray unchanged.
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