Guided Learning Plan
CUHKFAA Chan Chun Ha Secondary School
S3 Physics
Guided Learning Plan
Ch. 2 Refraction of Light
Name:____________________ Class:__________ Group:_________
P.1
Guided Learning Plan
2.1a Refraction of Light
Objectives:
1 To state Laws of refraction
Pre-learn Self-learning 自學
1. Textbook p.30-32
2. Experiment 2a
3 Read Examples in Textbook
4 Prepare your calculator, pencil, eraser and ruler.
Terms
refraction (折射) Snell's law (斯涅耳定律)
medium (介質) Laws of refraction
1 When a light ray enters a medium from another at an angle, it bends. The bending of light is called
refraction.
Expt 2a Refraction of light p.31
Objective
To find a law about the refraction of light by investigating the relationship between the angle of incidence and
the angle of refraction.
Set-up
1. Direct a ray of light to enter a semicircular glass block from its
straight edge. The light ray must hit the centre of the block (Fig a).
2. Measure the angle of incidence i and the angle of refraction r.
3. Repeat with other angles of incidence.
4. Record the results in a table.
5. Check the value of sin i / sin r for different value of i & r..
P.2
Guided Learning Plan
2 In Experiment 2a, the graph of sin i against sin r is a straight line passing through the origin (Fig 2a).
This means sin i directly proportional to sin r
3 When a ray of light passes from one medium to another, the refraction of light obeys the laws of refraction.
- The ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant,
sin i
= constant
sin r
- The incident ray, the refracted ray and the normal all lie in the same plane
sin i
4 The relationship = constant, is called Snell’s law. This is true for any pair of values of i and r.
sin r
The constant depends on the media across which light ray travels.
Check-point 1 (p.32)
Basic Exercise Co-learning 互學
1. The table below gives a set of results of the experiment. Complete the table. (3 marks)
(correct to 3 sig. fig.)
i 0o 20o 40o 60o 80o
r 0o 12.5o 24o 33.2o 38.6o
Sin i 0
Sin r 0
Sin i / sin r
P.3
Guided Learning Plan
Intermediate Exercise Cross-learning 共學
1. In an experiment, a light ray is incident on a semicircular glass block from air (Fig a). If r = 19.2 when
i = 30. Find r if i = 60. p.32 Eg 1
2. The figure shows a ray of light entering a glass block from air. It is known that the angle of refraction is
33o when the angle of incidence is 55o. When the angle of incidence is 66o, what is the angle of refraction?
(2 marks)
Key Concept
My learning progress 我的學習歷程
Number of mistakes I got (Please circle)
All correct or less than 3 mistakes Between 3-7 mistakes More than 7 mistakes
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go to the next part. this part again.
P.4
Guided Learning Plan
2.1b Refractive index & Snell’s Law
Objectives:
1 To realize Refractive index
2. Apply Snell’s law to solve problems
Pre-learn Self-learning 自學
1. Textbook p.33-35
2 Read Examples in Textbook
3 Prepare your calculator, pencil, eraser and ruler.
Terms
Snell's law (斯涅耳定律) refractive index (折射率)
5 Consider light travelling from air to another medium (e.g. glass). Then we define
where n is a constant called the refractive index of the medium.
6 The refractive index is a ratio and does not have a unit.
The refractive index of vacuum is __________.
7 Strictly speaking, n refers to a ray travelling from a vacuum to another medium. However it makes very
little difference if it is from air instead.
The refractive index of air therefore can be taken as __________.
8 Different media have different refractive indices. The larger the refractive index, the greater amount of
bending occurs in the medium.
9 In general, Snell’s law can be expressed as
n1 sin 1 =
where 1 and 2 stand for the two media that light crosses.
Check-point 2 (p.35)
P.5
Guided Learning Plan
Basic Exercise Co-learning 互學
1. Find the refractive index of the semicircular glass block in Example 1 (i = 30, r = 19.2). p.33 Eg 2
2. ind the refractive indices of the following unknown materials. (4 marks)
Intermediate Exercise Cross-learning 共學
1.
P.6
Guided Learning Plan
o
2. A ray of light passes from air into water. The angle of refraction is 28 . What is the angle of incidence?
(The refractive index of water is 1.33). (2 marks)
3. In the figure, a ray of light passes from air into a block of Perspex (n = 1.5). Find the angle of refraction.
(2 marks)
Key Concept
My learning progress 我的學習歷程
Number of mistakes I got (Please circle)
All correct or less than 3 mistakes Between 3-7 mistakes More than 7 mistakes
Excellent! Not bad. Not good.
->Please go to the next part. -> Please do the corrections and ->Please do revision and study
go to the next part. this part again.
P.7
Guided Learning Plan
2.1c Speed of light in different media
Objectives:
1 To realize the change of speed of light in different media
Pre-learn Self-learning 自學
1. Textbook p.35-37
2 Read Examples in Textbook
3 Prepare your calculator, pencil, eraser and ruler.
Terms
Optically denser media (光密介質) Optically less dense media (光疏介質)
10 Light travels at different speed in different media. Refraction results from the change in the direction of
light when it crosses a boundary.
11 The refractive index of a medium also equals the ratio of the speed of light in a vacuum (or air) to that in
the medium, i.e.
n =
where c and v are the speeds of light in a vacuum (or air) and the medium respectively.
12 The higher the refractive index of a medium, the smaller the speed of light in the medium.
13 A material with a larger refractive index is called an optically denser medium; a material with a smaller
refractive index is called an optically less dense medium.
14 When a light ray travels to an optically denser medium, the speed of light decreases and the ray is bent
____________________ the normal (Fig 2c).
When a light ray travels to an optically less dense medium, the speed of light increases and the ray is
bent _____________________ the normal (Fig 2d).
P.8
Guided Learning Plan
Basic Exercise Co-learning 互學
1. Draw the refracted ray in the diagram
Light travel to optically denser medium Light travel to optically less dense medium
2. The speed of light in air is 3 108 m s–1 and the speed of light in glass is 2 108 m s–1 Find the refractive
index (n) of glass. p.37 Eg 4
Check-point 3 (p.37)
My learning progress 我的學習歷程
Number of mistakes I got (Please circle)
All correct or less than 3 mistakes Between 3-7 mistakes More than 7 mistakes
Excellent! Not bad. Not good.
->Please go to the next part. -> Please do the corrections and ->Please do revision and study
go to the next part. this part again.
P.9
Guided Learning Plan
2.1d Examples of Refraction
Objectives:
To apply ray diagram to show examples of refraction of light
a Shallower in water
b Flickering objects
c Bent ruler
d Dispersion
Pre-learn Self-learning 自學
1. Textbook p.38-41
2 Read Examples in Textbook
3 Prepare your calculator, pencil, eraser and ruler.
Terms
apparent depth (視深) dispersion (色散)
real depth (實深) spectrum (光譜)
15 To an observer standing at poolside, the bottom of the pool seems to be at a higher position (Fig 2e), i.e.
the pool looks shallower
Fig 2e
16 The depth as seen by the observer is called the ___________________________ depth.
17 Different colours of light travel at slightly different speeds in materials. As a result they are refracted by
different amounts when they enter a material. When white light passes through a prism, it is refracted
twice and separated into different colours (Fig 2f).
A spectrum is formed and this effect is called dispersion.
red light, bent least
Fig 2f violet light, bent most Check-point 4 (p.41)
P.10
Guided Learning Plan
Basic Exercise Co-learning 互學
1. Draw ONE light rays to show how the observer see point P. (3 marks)
2. Write down the colour of the visible spectrum
Intermediate Exercise: Cross-learning 共學
1. A chopstick looks bent when dipped in water.
(a) Draw the image of chopstick in water. (1 mark)
(b) Draw ONE light ray to show how Andy sees the chopstick in water. (2 marks)
P.11
Guided Learning Plan
2. The bucket as shown appears to be shallower when filled with water (Fig a). The object at the bottom of
the bucket therefore appears (Fig b). p.39 Eg 5
Fig a Fig b
(a) Draw a ray diagram in Figure c to show how the observer sees the object.
(b) Indicate the apparent depth & real depth of the coin.
(a)
Figure c
Advanced Exericse (optional)
1 A diver in the sea looks at a bird above the water
(a) Draw a rays from the bird to the eye. (2 marks)
(b) Locate the apparent position of the bird. (1 mark)
P.12
Guided Learning Plan
2.2a Total internal reflection
Objectives:
1 To state the criteria for total internal reflection
Pre-learn Self-learning 自學
1. Textbook p.44-47
2. Experiment 2b
3 Complete questions 1-5 and Example 5
4 Prepare your calculator, pencil, eraser and ruler.
Terms
critical angle (臨界角)
total internal reflection (全內反射)
Expt 2b Total internal reflection p.44
Objective
To examine the conditions for total internal reflection.
Set-up
Fig a
Direct a ray of light to enter the semicircular block from its curved edge towards its centre O (Fig a). Slowly
increase the angle of incidence θg and watch how the refracted ray changes.
1 In Experiment 2b, the result will be different when the rays hitting the inside face of the semi-circular
block at different angles.
P.13
Guided Learning Plan
i The incident ray splits into two rays:
a reflected ray inside the Perspex (very weak) and
a refracted ray in the air.
Fig 2g
ii The incident ray also splits into two rays.
The angle of refraction becomes 90o and the
refracted ray just manages to leave the Perspex surface.
Fig 2h s
iii The incident ray is totally reflected inside the Perspex.
There is no refracted ray.
Fig 2i
2 Angle C in Figure 2h is called the critical angle. It is the angle of incidence at which the angle of
refraction is 90.
3 If a light ray hits the surface at an angle greater than the critical angle (Fig 2i), it is totally reflected
inside the block. This phenomenon is called Total internal reflection.
4 Total internal reflection only occurs for an incident ray in an optically denser medium.
5 Consider Figure 2h. According to Snell’s law,
n sin C = 1 sin 90
1
n
sin C
where n is the refractive index 折射率 of the medium.
Check-point 5 (p.47)
P.14
Guided Learning Plan
Basic Exercise Co-learning 互學
1. Given that the refractive indices of water and diamond are 1.33 and 2.42 respectively. Find the critical
angles of water and diamond. (3 marks)
2. Given that the critical angles of crystal and Perspex are 30o and 41.8o respectively. Find the refractive
indices of crystal and Perspex. (3 marks)
Intermediate Exercise Cross-learning 共學
1. A ray hits the inside face of a semicircular glass block. The following figures show the paths of the ray
with different angles of incidence.
(a) Find the refractive index of the glass block. (2 marks)
(b) Find the value of C. (2 marks)
(c) What will happen when angle of incidence is greater than C? (1 mark)
P.15
Guided Learning Plan
Advanced Exercise (optional)
1. A light ray enters a rectangular ice block of refractive index 1.31 from air as shown (Fig a). If the ray is
totally reflected on surface AB, what is the maximum value of angle ? p.46 Eg 7
air
ice
A B
Fig a
Hint: Find the critical angle C for the ice-air interface first.
2. Sketch the path of the rays in the following cases. (The refractive indices of water and Perspex are 1.33
and 1.5 respectively.)
My learning progress 我的學習歷程
Number of mistakes I got (Please circle)
All correct or less than 3 mistakes Between 3-7 mistakes More than 7 mistakes
Excellent! Not bad. Not good.
->Please go to the next part. -> Please do the corrections and ->Please do revision and study
go to the next part. this part again.
P.16
Guided Learning Plan
2.2b Examples of Total internal reflection
Objectives:
1 To draw ray diagram to show examples of total internal reflection
a Optical fibres光纖
b Using prisms 棱鏡 as mirrors
d Diamonds
Pre-learn Self-learning 自學
1. Textbook p.48-53
2 Complete questions and Examples
3 Prepare your calculator, pencil, eraser and ruler.
4. https://www.youtube.com/watch?v=0MwMkBET_5I
Terms
optical fibres (光導纖維)
prism (稜鏡)
6 In an optical fibre, the refractive index of the inner core is much greater than the outer cladding (Fig
2j).
Fig 2j
7 A prism behaves like a perfect mirror if light rays are incident on its inside face at an angle greater than
the critical angle. They do not form multiple images as plane mirrors do (Fig 2k).
Fig 2k
P.17
Guided Learning Plan
9 Diamonds sparkle because they easily reflect back light which goes into them due to their large
refractive index (Fig 2m).
Best cutting angle Cutting too deep 深 Cutting too shallow 淺
P.18
Guided Learning Plan
Basic Exercise Co-learning 互學
1. What is the advantage of using prism as mirror. (2 marks)
2. Given that the critical angles of diamond and glass are 24.40 and 41.8o respectively. Explain briefly why
diamond is more brilliant than glass. (3 marks)
Intermediate Exercise Cross-learning 共學
A ray of light is incident from glass into water (Fig a). The refractive index of glass is 1.6 and that of water is
1.33.
glass
water
(a) Calculate the critical angle for the glass-water interface.
(b) Will the ray be totally reflected if the glass and water layer is reversed?
P.19
Guided Learning Plan
Advanced Exercise (optional)
My learning progress 我的學習歷程
Number of mistakes I got (Please circle)
All correct or less than 3 mistakes Between 3-7 mistakes More than 7 mistakes
Excellent! Not bad. Not good.
->Please go to the next part. -> Please do the corrections and ->Please do revision and study
go to the next part. this part again.
P.20
Guided Learning Plan
2.2c Examples Total internal reflection
Objectives:
1 To draw ray diagram to show examples of total internal reflection
c Mirages 海市蜃樓
2 To draw ray diagram to show examples of total internal reflection Fish-eye view
Pre-learn Self-learning 自學
1 Textbook p.54-56
2 Complete questions and Examples
3 Prepare your calculator, pencil, eraser and ruler.
4. https://www.youtube.com/watch?v=QnMP0jtLo9A
Term
mirage (海市蜃樓)
Fish-eye view
8 The road appears wet on a hot day because of total internal reflection (Fig 2l). What we see is only the
reflection of the sky. This type of illusion is called a mirage
Fig 2l
P.21
Guided Learning Plan
10 The view under water is squeezed into a cone with an angle of about 98o (Fig 2n).
Fig 2n
P.22
Guided Learning Plan
Basic Exercise Co-learning 互學
1. Draw the refracted ray inside optical fibre
2. Complete the paths of the rays.
Intermediate Exercise Cross-learning 共學
1. A diver looks upwards under the water. The diameter of his view is 10m. The refractive index of water
is 1.33.
(a) Find the critical angle of water. (2 marks)
(b) Find the depth of his eye under the water. (2 marks)
P.23
Guided Learning Plan
Key Concept
My learning progress 我的學習歷程
Number of mistakes I got (Please circle)
All correct or less than 3 mistakes Between 3-7 mistakes More than 7 mistakes
Excellent! Not bad. Not good.
->Please go to the next part. -> Please do the corrections and ->Please do revision and study
go to the next part. this part again.
P.24
