Transcript SNC2D - SECTION 11.1 - St. Jean de Brebeuf Home Page

Partial Refraction and
Total Internal
Reflection
Section 11.2
Pg. 457-467
SNC2D
Review of Refraction
Light travelling from one medium to another is
both reflected and refracted. This is called
partial reflection and refraction.
Light will bend (refraction):
• Toward the normal when it slows down
(angle of refraction is smaller than angle of
incidence)
• Away from the normal when it speeds up
at the boundary of two media.
The amount of reflection compared with the
amount of refraction depends on the angle of
incidence as well as the relative incides of
refraction of the two media.
- As shown in the images below, the reflection of sunlight
is far greater when the sun is low in the sky (B - sunset)
than when it is directly overhear (A - midday).
Reflection and Refraction in a
Rearview Mirror
Rearview mirrors are wedge-shaped and silvered
on the back.
 In the daytime, the mirror is positioned so that
the light that has reflected off the back of the
mirror is directed to the driver’s eye.
 At night, the driver can flip a switch that tilts the
mirror so that only a small amount of reflected
light is directed toward the driver’s eyes.

Refraction cont’d ...
Less dense
More dense
Light will bend away from the normal when it
speeds up at the boundary of two media.
 As the angle of incidence increases, the angle of
refraction will also increase.
 The angle of refraction will continue to increase
as the angle of incidence increases until it
becomes 90°

Refraction cont’d ...
Angle of
refraction = 90°
Less dense
More dense

The angle of incidence that produces a refracted
angle of 90° is called the critical angle.
(A) When the angle of incidence is smaller than the
critical angle, both refraction and reflection occur at
the boundary between the two media.
(B) When the angle of refraction reaches 90°, the
refracted ray lies along the boundary between the
two media.
(C) When the angle of incidence is larger than the
critical angle, all the light is reflected back into the first
medium.
Total Internal Reflection (TIR)

If you increase the angle of incidence past the critical
angle, the refracted ray will no longer exit the
medium.

The ray will reflect back in the medium.

This is called Total Internal Reflection (TIR).
Conditions for Total Internal
Reflection (TIR)
1.
Light is travelling slower in the first
medium than in the second.
2.
The angle of incidence is large enough
that no refraction occurs in the
second medium. Instead, the ray is
reflected back into the first medium.
HOMEWORK:
Read Pg. 457-467
and make notes
Applications of TIR
Diamonds
Retroreflectors
Fibre Optics
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Use of Fibre Optics:
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Telecommunication
Automotives
Medicine
Homework
Read pg. 449-456
 Answer # 1-4 on pg. 455
 Answer # 1-8 on pg. 456
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