The Nature and Propagation of Light - erickorevaar.comerickorevaar.com/assets/33_Lecture_Outline_Merged.pdfPowerPoint® Lectures for University Physics, Thirteenth Edition – Hugh

Copyright © 2012 Pearson Education Inc.

PowerPoint® Lectures for

University Physics, Thirteenth Edition

– Hugh D. Young and Roger A. Freedman

Lectures by Wayne Anderson

Chapter 33

The Nature and

Propagation of Light


Goals for Chapter 33

• To understand light rays and wavefronts

• To analyze reflection and refraction of light

• To understand total internal reflection

• To analyze the polarization of light

• To use Huygens’s principle to analyze reflection

and refraction


Introduction

• Why does a rainbow of colors

appear when these tools are

placed between polarizing

filters?

• Our study of light will help us

understand why the sky is

blue and why we sometimes

see a mirage in the desert.

• Huygens’s principle will

connect the ray and wave

models of light.


The nature of light

• Light has properties of

both waves and particles.

The wave model is

easier for explaining

propagation, but some

other behavior requires

the particle model.

• The rays are

perpendicular to the

wave fronts. See Figure

33.4 at the right.


Reflection and refraction

• In Figure 33.5 the light is both reflected and refracted by the window.


Specular and diffuse reflection

• Specular reflection occurs at a very smooth surface (left figure).

• Diffuse reflection occurs at a rough surface (right figure).

• Our primary concern is with specular reflection.


Laws of reflection and refraction

• The index of refraction is n = c/v >1.

• Angles are measured with respect to the normal.

• Reflection: The angle of reflection is equal to the angle of incidence.

• Refraction: Snell’s law applies.

• In a material = 0/n.

• Figure 33.7 (right) illustrates the laws of reflection and refraction.


When light passes from vacuum (index of refraction n = 1)

into water (n = 1.333),

Q33.1

A. the wavelength increases and the frequency is unchanged.

B. the wavelength decreases and the frequency is unchanged.

C. the wavelength is unchanged and the frequency increases.

D. the wavelength is unchanged and the frequency decreases.

E. both the wavelength and the frequency change.


When light passes from vacuum (index of refraction n = 1)

into water (n = 1.333),

A33.1

A. the wavelength increases and the frequency is unchanged.

B. the wavelength decreases and the frequency is unchanged.

C. the wavelength is unchanged and the frequency increases.

D. the wavelength is unchanged and the frequency decreases.

E. both the wavelength and the frequency change.


Reflection and refraction in three cases

• Figure 33.8 below shows three important cases:

If nb > na, the refracted ray is bent toward the normal.

If nb < na, the refracted ray is bent away from the normal.

A ray oriented along the normal never bends.


Light passes from vacuum (index of refraction n = 1) into

water (n = 1.333).

If the incident angle qa is in the range 0° < qa < 90°,

Q33.2

A. the refracted angle is greater than the incident angle.

B. the refracted angle is equal to the incident angle.

C. the refracted angle is less than the incident angle.

D. the answer depends on the specific value of qa .


Light passes from vacuum (index of refraction n = 1) into

water (n = 1.333).

If the incident angle qa is in the range 0° < qa < 90°,

A33.2

A. the refracted angle is greater than the incident angle.

B. the refracted angle is equal to the incident angle.

C. the refracted angle is less than the incident angle.

D. the answer depends on the specific value of qa .


Light passes from a medium of index of refraction na into a

second medium of index of refraction nb. The angles of

incidence and refraction are qa and qb, respectively.

If na < nb,

Q33.3

Aqa > qb and the light speeds up as it enters the second medium.

B. qa > qb and the light slows down as it enters the second medium.

C. qa < qb and the light speeds up as it enters the second medium.

D. qa < qb and the light slows down as it enters the second medium.



second medium of index of refraction nb. The angles of

incidence and refraction are qa and qb, respectively.

If na < nb,

A33.3

Aqa > qb and the light speeds up as it enters the second medium.

B. qa > qb and the light slows down as it enters the second medium.

C. qa < qb and the light speeds up as it enters the second medium.

D. qa < qb and the light slows down as it enters the second medium.


Why does the ruler appear to be bent?

• The straight ruler in Figure 33.9(a) appears to bend at the surface of the water.

• Figure 33.9(b) shows why.


Some indexes of refraction


An example of reflection and refraction

• Read Problem-Solving Strategy 33.1.

• Follow Example 33.1 which involves both reflection and refraction. Use Figure 33.11 below.


The eye and two mirrors

• Follow Example 33.2 which looks at the eye.

• Follow Example 33.3 which involves reflection from two mirrors. Use Figure 33.12 below.


Total internal reflection

• Light striking at the critical angle emerges tangent to the surface. (See Figure 33.13 below.)

• If qa > qcrit, the light is undergoes total internal reflection.


Q33.4


second medium of index of refraction nb. The critical angle for

total internal reflection is qcrit.

In order for total internal reflection to occur, what must be true

about na, nb, and the incident angle qa?

A. na > nb and qa > qcrit

B. na > nb and qa < qcrit

C. na < nb and qa > qcrit

D. na < nb and qa < qcrit



second medium of index of refraction nb. The critical angle for

total internal reflection is qcrit.

In order for total internal reflection to occur, what must be true

about na, nb, and the incident angle qa?

A33.4

A. na > nb and qa > qcrit

B. na > nb and qa < qcrit

C. na < nb and qa > qcrit

D. na < nb and qa < qcrit


Some applications of total internal reflection

• A binocular using Porro prisms (below) and a “light pipe” (right) make use of total internal reflection in their design.


A diamond and a periscope

• Diamonds sparkle because they are cut so that total internal reflection occurs on their back surfaces. See Figure 33.17 below.

• Follow Conceptual Example 33.4.


Dispersion

• Dispersion: The index of refraction depends on the wavelength of the light. See Figure 33.18 (right).

• Figure 33.19 (below) shows dispersion by a prism.


Rainbows—I

• The formation of a rainbow is due to the combined effects of

dispersion, refraction, and reflection. (See Figure 33.20 below

and on the next slide.)


Rainbows—II


Polarization

• An electromagnetic wave is linearly polarized if the electric field has only one component.

• Figure 33.23 at the right shows a Polaroid polarizing filter.


Malus’s law

• Figure 33.25 below shows a polarizer and an analyzer.

• Malus’s law: I = Imaxcos2.

• Read Problem-Solving Strategy 33.2.

• Follow Example 33.5.


Three polarizing filters are stacked with the polarizing axes of

the second and third filters oriented at 45° and 90°, respectively,

relative to the polarizing axis of the first filter. Unpolarized

light of intensity I0 is incident on the first filter. The intensity of

light emerging from the third filter is

Q33.5

0

0

0

0

0

A. .

B. / 2.

C. / 2.

D. / 4.

E. /8.

I

I

I

I

I


A33.5

Three polarizing filters are stacked with the polarizing axes of

the second and third filters oriented at 45° and 90°, respectively,

relative to the polarizing axis of the first filter. Unpolarized

light of intensity I0 is incident on the first filter. The intensity of

light emerging from the third filter is

0

0

0

0

0

A. .

B. / 2.

C. / 2.

D. / 4.

E. /8.

I

I

I

I

I


Polarization by reflection

• When light is reflected at the polarizing angle qp, the reflected

light is linearly polarized. See Figure 33.27 below.


Brewster’s law

• Brewster’s law: tan qp = nb/na.

• At the polarizing angle, the reflected and refracted rays are perpendicular to each other. See Figure 33.28 at the right.


Natural light is incident on the surface of a liquid.

The reflected light will be completely polarized if

the incident angle qa is

Q33.6

A. greater than the polarizing angle.

B. greater than or equal to the polarizing angle.

C. equal to the polarizing angle.

D. less than or equal to the polarizing angle.

E. less than the polarizing angle.


Natural light is incident on the surface of a liquid.

The reflected light will be completely polarized if

the incident angle qa is

A33.6

A. greater than the polarizing angle.

B. greater than or equal to the polarizing angle.

C. equal to the polarizing angle.

D. less than or equal to the polarizing angle.

E. less than the polarizing angle.


Reflection from a swimming pool

• Follow Example 33.6 using Figure 33.29 below.


Circular polarization

• Circular polarization results from the superposition of two perpendicularly polarized electromagnetic waves having equal amplitude but a quarter-cycle phase difference. The result is that the electric field vector has constant amplitude but rotates about the direction of propagation. (Figure 33.30 below.)


Scattering of light

• Scattering occurs when light has been absorbed by molecules and reradiated.

• Figure 33.32 below shows the effect of scattering for two observers.


Why are clouds white?

• Clouds are white because they scatter all wavelengths efficiently. See Figure 33.33 below.


Huygens’s principle

• Huygens’s principle: Every point of a wave front can be considered to be a source of secondary wavelets that spread out in all directions with a speed equal to the speed of propagation of the wave. See Figure 33.34 at the right.


Reflection and Huygens’s principle

• Figure 33.35 at the right shows how Huygens’s principle can be used to derive the law of reflection.


Refraction and Huygens’s principle

• Huygens’s principle can be used to derive the law of reflection.

• Follow the text analysis using Figure 33.36 below.


A mirage

• Huygens’s principle can also explain the formation of a mirage. See Figure 33.37 below.

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The Nature and Propagation of Light - erickorevaar.comerickorevaar.com/assets/33_Lecture_Outline_Merged.pdfPowerPoint® Lectures for University Physics, Thirteenth Edition – Hugh