Refraction of the light
What about the light?
What about the light?
Photon emission
Representation of light
Photon
Representation of light
Photon
Representation of light
Photon
Representation of light
Representation of light
S
Representation of light
S
Representation of light
S
Representation of light
S
Why this pencil seems broken?
Why this pencil seems broken?
Refraction!
Refraction is the bending of light as it passes from one
substance to another
Refraction is the bending of light as it passes from one
substance to another
Air
Glass
Vocabulary of Refraction
incident ray
interface
inc
Air
Water
Vocabulary of Refraction
incident ray
interface
refracted ray
inc
refr
Air
Water
Vocabulary of Refraction
incident ray
interface
reflected ray
inc
refl
Air
Water
refracted ray
refr
Vocabulary of Refraction
incident ray
interface
reflected ray
inc
refl
inc= refl
Air
Water
refracted ray
refr
Vocabulary of Refraction
incident ray
interface
reflected ray
refracted ray
inc
refr
refl
inc= refl
Air
Water
Vocabulary of Refraction
incident ray
interface
reflected ray
refracted ray
inc
refr
refl
inc= refl
P
Air
Water
Vocabulary of Refraction
incident ray
interface
reflected ray
refracted ray
inc
refr
refl
inc= refl
P
Air
Water
nair
nwater
Snell-Descartes Law
incident ray
interface
refracted ray
inc
refr
Air
Water
nwater
nair
Snell-Descartes Law
incident ray
interface
refracted ray
inc
refr
Air
Water
nwater
nair
nair. sin inc = nwater. sin refr
Snell-Descartes Law
incident ray
interface
refracted ray
inc
refr
Air
Water
nwater
nair
nair. sin inc = nwater. sin refr
n1. sin inc = n2. sin refr
Snell-Descartes Law
incident ray
interface
refracted ray
inc
refr
Air
Water
nwater
nair
nair. sin inc = nwater. sin refr
n1. sin inc = n2. sin refr
nair =1
nwater =1.5
inc= 45
Snell-Descartes Law
incident ray
interface
refracted ray
inc
refr
Air
Water
nwater
nair
nair. sin inc = nwater. sin refr
n1. sin inc = n2. sin refr
nair =1
nwater =1.5
inc= 45
sin refr= (nair. sin inc) / nwater
Snell-Descartes Law
incident ray
interface
refracted ray
inc
refr
Air
Water
nwater
nair
nair. sin inc = nwater. sin refr
n1. sin inc = n2. sin refr
nair =1
nwater =1.5
inc= 45
sin refr= (nair. sin inc) / nwater
= 0.71/1.5
= 0.47
Snell-Descartes Law
incident ray
interface
refracted ray
inc
refr
Air
Water
nwater
nair
nair. sin inc = nwater. sin refr
n1. sin inc = n2. sin refr
nair =1
nwater =1.5
inc= 45
sin refr= (nair. sin inc) / nwater
= 0.71/1.5
= 0.47
refr = arcsin 0.47
=28.13
Snell-Descartes Law
i
n1
n1
n2
n1 < n2
i
n1
n1
n2
n1 > n2
i
Snell-Descartes Law
n1 < n2
r
i < r
n1 > n2
i
n1
n1
n2
r
i > r
i
i
n1
n1
n2
n1 > n2
Snell-Descartes Law
r
i < r
n1 > n2
i
n1
n1
n2
n1 > n2
Snell-Descartes Law
r
i < r
n1 > n2
i
n1
n1
n2
n1 > n2
Snell-Descartes Law
r
i = r
n1 > n2
i
n1
n1
n2
n1 > n2
The broken pencil
Air
Water
Eye
The broken pencil
Air
Water
Eye
The broken pencil
Air
Water
Eye
The broken pencil
Air
Water
Eye
Exercices& Applications
Optical Fiber
An optical fiber is a thread in glass or plastic which has the
property to drive the light. To drive the light without leak or
loss, we have to avoid phenomenoms of refraction inside the thread.
In order to avoid it, the thread is constituted by a core (index
n1) and a duct (index n2).
n2
n1
air
1
1. Write the Snell-Descartes law for the interface between air
and the core of the optical fiber.
2. What will be the value of 1 for air = 25 , nair=1 and n1=1.4?
How will 1 evolve if n1> 1.4?
Core
Duct
Optical Fiber
An optical fiber is a thread in glass or plastic which has the
property to drive the light. To drive the light without leak or
loss, we have to avoid phenomenoms of refraction inside the thread.
In order to avoid it, the thread is constituted by a core (index
n1) and a duct (index n2).
n2
n1
air
1
3. Find a condition on n2 to avoid the refraction and have a
total reflection.Clue: What is the critical value of an angle of
refraction?
n2
n1
1
Core
Duct
Cold or warm mirages?
The index of air is decreasing with the temperature (nwarm <
ncold). Mirages are manifestations of this variation. When the
variation of temperature is important the refraction bends the path
of the light, like with the pencil in water, except here there is a
succession of different interfaces.
n1
n4
n3
n2
n5
Eye
Eye
Actually, there are two kinds of mirages: warm and cold.Warm
mirages can be observed in warm area, and cold mirages in cold
area.
Warm Mirage
Cold Mirage
1. Can you explain why warm mirages are in warm area?
2. Same question for the cold mirage
Push on Start button!
Push again when you are ready to have the correction!
Optical Fiber
An optical fiber is a thread in glass or plastic which has the
property to drive the light. To drive the light without leak or
loss, we have to avoid phenomenoms of refraction inside the thread.
In order to avoid it, the thread is constituted by a core (index
n1) and a duct (index n2).
n2
n1
air
1
1. Write the Snell-Descartes law for the interface between air
and the core of the optical fiber.
2. What will be the value of 1 for air = 25 , nair=1 and n1=1.4?
How will 1 evolve if n1> 1.4?
Core
Duct
nair. sin air = n1. sin 1
nair. sin air = n1. sin 1 1 = arcsin (nair. sin air / n1 ) =
17.6
If n1 > 1.4, 1 < 17.6
Optical Fiber
An optical fiber is a thread in glass or plastic which has the
property to drive the light. To drive the light without leak or
loss, we have to avoid phenomenoms of refraction inside the thread.
In order to avoid it, the thread is constituted by a core (index
n1) and a duct (index n2).
n2
n1
air
1
3. Find a condition on n2 to avoid the refraction and have a
total reflection.Clue: What is the critical value of an angle of
refraction?
n2
n1
1
Core
Duct
1
2
2 = 90 So, sin 2 = 1
1
1
Snell-Descartes law: n1.sin 1 = n2
If n1.sin 1 > n2 , refraction can't occure.
1= 180 (90 + 1 )
For 1 = 17.6 and n1 = 1.4
n2
