total internal reflect
DESCRIPTION
Physics CrapTRANSCRIPT
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Total internal reflection
Form 4 PhysicsForm 4 PhysicsForm 4 PhysicsForm 4 Physics
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Group 14
Members: Name Student number Job
Sun Lun Chi S98006900 Leader Original scriptCheng Shu Wing S98007150 Second stage productionLee Yan Ming S98007800 IllustrationsTang Yuk Man S98006810 Additional ScriptsYau Yat Fai S98007070 Animations & SFX
November 1998
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Lecture presentationfor Form 4
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Contents• Reflection and refraction (revision)
• Critical angle
• Total internal reflection
• Fish eye view
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glass
Reflection and refraction• Mirror reflects light
• Transparent medium refracts lightmirror
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Which angle is larger?• A light ray is emerging from glass to air.
Which angle is larger, in glass or in the air ?
glassnormal
Or this?
This?AIR
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glass
Which angle is larger?• A light ray is emerging from glass to air.
Which angle is larger, in glass or in the air ?
normal
Or this?
This?
Next
AIR
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Critical angle (1)• For glass-air interface, the angle of refraction in
air > incident angle
glass
AIR
normal
Incident angle
Angle of refraction
Partial reflection
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Which angle first?If the angle of incidence increases, which angle will reach 90o first, the angle of incidence or the angle of refraction?
A Angle of incidence (from glass)
B Angle of refraction (in the air)
Next
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AIR
Critical angle (2)• When we increase the angle of incidence (i), the
angle of refraction (r) increases until ......
AIR
glassglass
AIR
glass
AIR
glass
i
r
normal
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AIR
glass
Critical angle (3)• when the angle of refraction is 90o, the incident
angle is called the critical angle (C).
AIR
glass
r90o
normal
iC
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sin 90o
sin C
Critical angle (4)• For glass-air interface, the critical angle is 42o.
• At critical angle, angle of refraction is 90o, so, by the laws of refraction,
n =sin rsin i
=1
n x sin C = 1
sin C =1n
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What is the critical angle...… for water-air interface?
The refractive index of water is 1.33
sin C =1n
1 ÷ 1.33 = 0.75
sin-1 0.75 = 48.8o
=> C = 48.8o
I can do it,
so can you!
Check :
sin C = sin 48.8o = 0.75
1 ÷ 0.75 = 1.33
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For glass, the refractive index is 1.5;
C = sin-1 (1÷1.5)Critical angle = 42o
Critical angle (5)
sin C =1n
For water, the refractive index is 1.33;
C = sin-1 (1÷1.33)Critical angle = 48.8o
1n
C = sin-1 ( )
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What if ...… the angle of incidence (from glass) is larger than the critical angle?
A The angle of refraction will become
smaller again.
B There will be no refracted ray.
C The light ray will be reflected the
same way back.
Next
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Total internal reflection (1)• When the light ray (from water) is emerging at
the critical angle, the refracted ray will be along the interface.
water
AIR
alongalong
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Total internal reflection (2)• When the incident angle is larger than the
critical angle, total internal reflection will occur (at the interface).
water
AIR
Next
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Total internal reflection (3)• View under water!!
water
AIR
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Total internal reflection (4)• Fish-eye view
You see
total internal
reflection here
You see the sky here
through refraction
You seewater waves
here
total internalreflection here
total internalreflection here
skywaves
waves
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Can you explain the ...• fish-eye view by drawing light rays?
water
Yes
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Fish eye view (1)
water
Central hole, shows thesqueezed view of the sky
totally internallyreflected ray
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Fish eye view (2)• When a diver or fish looks upward under water,
part of the water surface looks like a mirror, except the central hole.
• So, the light entering the water from above the surface is squeezed into a cone of angle 2C
2C
water
What is C ?
C is critical angle
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Revisit the fish eye view• Do you remember which part has refraction and
which part has total internal reflection?
total internalreflection here
sky(refraction here)
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What did you learn?
• Critical angle
• Total internal reflection occurs when a light ray tries to escape from water (or glass) to air at an angle of incidence larger than the critical angle at the interface.
• Fish eye view is an example of total internal reflection and refraction.
1n
C = sin-1 ( )
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