chapter 35

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{{Chapter 35Chapter 35

Interference (cont.)Interference (cont.)


Interference in thin filmsInterference in thin films

• Figure 35.11 (right) Figure 35.11 (right) shows why thin-film shows why thin-film interference occurs, interference occurs, with an illustration.with an illustration.

• Figure 35.12 (below) Figure 35.12 (below) shows interference of shows interference of an air wedge. an air wedge.


Phase shifts during reflectionPhase shifts during reflection

• Follow the text analysis of thin-film interference and Follow the text analysis of thin-film interference and phase shifts during reflection. Use Figure 35.13 below.phase shifts during reflection. Use Figure 35.13 below.


A. /2.

B. 3/4.

C. .

D. either A. or C.

E. any of A., B., or C.

Q35.6

An air wedge separates two glass plates as shown. Light of wavelength strikes the upper plate at normal incidence. At a point where the air wedge has thickness t, you will see a bright fringe if t equals


A35.6

An air wedge separates two glass plates as shown. Light of wavelength strikes the upper plate at normal incidence. At a point where the air wedge has thickness t, you will see a bright fringe if t equals

A. /2.

B. 3/4.

C. .

D. either A. or C.

E. any of A., B., or C.


Newton’s rings Newton’s rings

• Figure 35.16 below illustrates the Figure 35.16 below illustrates the interference rings (called interference rings (called Newton’s ringsNewton’s rings) ) resulting from an air film under a lens.resulting from an air film under a lens.


Using interference fringes to test a lensUsing interference fringes to test a lens• The lens to be The lens to be

tested is tested is placed on top placed on top of the master of the master lens. If the lens. If the two surfaces two surfaces do not match, do not match, Newton’s Newton’s rings will rings will appear, as in appear, as in Figure 35.17 Figure 35.17 at the right.at the right.


{{Chapter 36Chapter 36

DiffractionDiffraction


DiffractionDiffraction• According to geometric optics, a light source shining on an According to geometric optics, a light source shining on an

object in front of a screen should cast a sharp shadow. object in front of a screen should cast a sharp shadow. Surprisingly, this does not occur because of Surprisingly, this does not occur because of diffractiondiffraction..


Diffraction and Huygen’s PrincipleDiffraction and Huygen’s Principle

• Fresnel diffractionFresnel diffraction: Source, screen, and obstacle are close : Source, screen, and obstacle are close together.together.

• Fraunhofer diffractionFraunhofer diffraction: Source, screen, and obstacle are far : Source, screen, and obstacle are far apart.apart.

• Figure 36.2 below shows the diffraction pattern of a razor blade.Figure 36.2 below shows the diffraction pattern of a razor blade.


Diffraction from a single slitDiffraction from a single slit• In Figure 36.3 below, the prediction of geometric optics in

(a) does not occur. Instead, a diffraction pattern is produced, as in (b).


Fresnel and Fraunhofer diffraction by a single Fresnel and Fraunhofer diffraction by a single slitslit

• Figure 36.4 below shows Fresnel (near-field) and Frauenhofer (far-field) diffraction for a single slit.


Locating the dark fringesLocating the dark fringes

• Figure 36.5 below shows the geometry for Fraunhofer Figure 36.5 below shows the geometry for Fraunhofer diffraction.diffraction.


An example of single-slit diffractionAn example of single-slit diffraction

• Figure 36.6 (bottom left) is a photograph of a Figure 36.6 (bottom left) is a photograph of a Fraunhofer pattern of a single horizontal slit.Fraunhofer pattern of a single horizontal slit.


Intensity maxima in a single-slit patternIntensity maxima in a single-slit pattern

• Figure 36.9 at the right shows the Figure 36.9 at the right shows the intensity versus angle in a single-slit intensity versus angle in a single-slit diffraction pattern.diffraction pattern.

• Part (b) is photograph of the Part (b) is photograph of the diffraction of water waves.diffraction of water waves.


Width of the single-slit patternWidth of the single-slit pattern

• The single-slit diffraction pattern depends on the ratio of The single-slit diffraction pattern depends on the ratio of the slit width the slit width aa to the wavelength to the wavelength . (Figure 36.10 below.). (Figure 36.10 below.)


Q36.1

A. Double the slit width a and double the wavelength .

B. Double the slit width a and halve the wavelength .

C. Halve the slit width a and double the wavelength .

D. Halve the slit width a and halve the wavelength .

Light of wavelength passes through a single slit of width a. The diffraction pattern is observed on a screen that is very far from from the slit.

Which of the following will give the greatest increase in the angular width of the central diffraction maximum?


A36.1

A. Double the slit width a and double the wavelength .

B. Double the slit width a and halve the wavelength .

C. Halve the slit width a and double the wavelength .

D. Halve the slit width a and halve the wavelength .

Light of wavelength passes through a single slit of width a. The diffraction pattern is observed on a screen that is very far from from the slit.

Which of the following will give the greatest increase in the angular width of the central diffraction maximum?


In a single-slit diffraction experiment with waves of wavelength , there will be no intensity minima (that is, no dark fringes) if the slit width is small enough.

What is the maximum slit width a for which this occurs?

Q36.2

A. a =

B. a =

C. a = 2

D. The answer depends on the distance from the slit to the screen on which the diffraction pattern is viewed.


In a single-slit diffraction experiment with waves of wavelength , there will be no intensity minima (that is, no dark fringes) if the slit width is small enough.

What is the maximum slit width a for which this occurs?

A36.2

A. a =

B. a =

C. a = 2

D. The answer depends on the distance from the slit to the screen on which the diffraction pattern is viewed.


Two slits of finite widthTwo slits of finite width

• For slits extremely narrow, behaves very close to ideal case from previous chapter

• For wider slits, behaves like a combination of single-slit diffraction and double-slit interference.


Interference pattern of several slitsInterference pattern of several slits

• Figure 36.15 below shows the interference pattern for 2, 8, and 16 Figure 36.15 below shows the interference pattern for 2, 8, and 16 equally spaced narrow slits.equally spaced narrow slits.


In Young’s experiment, coherent light passing through two slits separated by a distance d produces a pattern of dark and bright areas on a distant screen.

If instead you use 10 slits, each the same distance d from its neighbor, how does the pattern change?

Q36.3

A. The bright areas move farther apart.

B. The bright areas move closer together.

C. The spacing between bright areas remains the same, but the bright areas become narrower.

D. The spacing between bright areas remains the same, but the bright areas become broader.


In Young’s experiment, coherent light passing through two slits separated by a distance d produces a pattern of dark and bright areas on a distant screen.

If instead you use 10 slits, each the same distance d from its neighbor, how does the pattern change?

A36.3

A. The bright areas move farther apart.

B. The bright areas move closer together.

C. The spacing between bright areas remains the same, but the bright areas become narrower.

D. The spacing between bright areas remains the same, but the bright areas become broader.

chapter 35

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