Partial Refraction Partial Refraction and Total Internal and Total Internal ReflectionReflection

Section 11.2Pg. 457-467SNC2D

Review of RefractionReview of RefractionLight 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 Reflection and Refraction in a Rearview Mirrora 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 ...Refraction cont’d ...

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°

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Refraction cont’d ...Refraction cont’d ...

The angle of incidence that produces a refracted angle of 90° is called the critical angle.

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Angle of refraction = 90°

(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. 457-467and make notes

Applications of TIR Diamonds Retroreflectors Fibre Optics

◦ Use of Fibre Optics: Telecommunication Automotives Medicine

HomeworkHomeworkRead pg. 449-456Answer # 1-4 on pg. 455Answer # 1-8 on pg. 456