Chapter 29Chapter 29

Light WavesLight Waves

1.1. HUYGENS' PRINCIPLEHUYGENS' PRINCIPLE

Every point on a wave front can be regarded as a new source of wavelets, which combine to produce the next wave front, whose points are sources of further wavelets, and so on.

Huygen’s Principle can be used to explain the propagation of wave

fronts involved in reflection, refraction, and diffraction.

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Consider several points on the wave front

to be sources of secondary wavelets.

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2.2. DIFFRACTIONDIFFRACTION

The bending of light that passes around an obstacle or through a narrow slit, causing the light to spread and to produce light and dark fringes.

Demo - Laser, diffraction accessories, and Demo - Laser, diffraction accessories, and rainbow disks rainbow disks

If the wavelength of water waves are small

compared to the size of an ocean vessel, the

vessel will cast a “shadow.”

For the same waves a stick will not cast a

“shadow.”

Long wavelengths bend a great deal around small objects.

Because of diffraction AM radio waves travel farther than FM radio waves.

Microscopy diffraction limit -

One cannot see details of objects that are approximately the same size as or smaller than the wavelength of the illuminating light.

3.3. INTERFERENCEINTERFERENCE

SlideSlide - Interference Transparencies - Interference Transparencies

Demo - Finger slit interferenceDemo - Finger slit interference

Demo - Single-color thin film interferenceDemo - Single-color thin film interference

Demo - Optical flats and sodium lampDemo - Optical flats and sodium lamp

Demo - Newton's rings and phase reversalDemo - Newton's rings and phase reversal

Interference Colors by Reflection from Thin Films

Iridescence - the phenomenon of seeing

colors by interference in thin films.

Demo - Soap bubbles and pipeDemo - Soap bubbles and pipe

Demo - Peacock feathersDemo - Peacock feathers

Example - Coated photographic lenses

Interferometers measure small distances.

Thin Film t

Air

Air

Phase Reversal

upon reflection

Path Difference = 2t = n for destructive interference

Thus t = n(/2)

n = 1,2,3,4,…… You see the complement of whichever color is destructively interfered with.

4. POLARIZATION

Video - Polarization DiagramPolarization Diagram Video - Crossed PolaroidsCrossed Polaroids Demo - PolaroidsDemo - Polaroids

Light waves are transverse. This is verified by polarization.

Common sources of light are not polarized. Polaroid Crystals - one axis direction

absorbs, one transmits. Polarized glare occurs on reflection from

nonmetallic surfaces.

COLORS BY TRANSMISSION THROUGH POLARIZING MATERIALS

Video - Crossed Polaroids and Crystal Video - Crossed Polaroids and Crystal Video - Polarizers and StressVideo - Polarizers and Stress Demo - Polaroids and accessoriesDemo - Polaroids and accessories

Three-Dimensional Viewing

Stereoscopic viewersSlideSlide - Stereogram

5. HOLOGRAPHY

Hologram means whole message.

Demo - Reflection hologramDemo - Reflection hologram

Demo - Transmission hologramDemo - Transmission hologram

No lenses are used for imaging in the

creation or the viewing of a hologram.

Object and source both illuminateboth illuminate all of the

photographic plate.

The light used to make the hologram

must be coherent.

A hologram is an interference pattern.

It is best to use coherent light when viewingviewing a

hologram.

A hologram can be divided.

One gets a magnified holographic image by

viewing a hologram with a longer  of light

than was used in creating the hologram.

Chapter 29 Review QuestionsChapter 29 Review Questions

AM band radio waves travel farther than FM band radio waves because

(a) AM waves travel faster than FM waves(b) AM wavelengths are shorter than FM

wavelengths(c) AM waves are scattered more than FM

waves(d) AM waves are diffracted more than FM

waves

(d) AM waves are diffracted more than FM waves

If laser light passes by a hair, a pattern of light and dark can be seen on a properly placed screen. What phenomenon (phenomena) is (are) being observed?

(a) diffraction

(b) polarization

(c) chromatic aberration

(d) all of the above

(e) none of the above

(a) diffraction

Polaroid sunglasses worn in a normal viewing position will eliminate polarized

glare.

(a) vertically

(b) horizontally

(c) all

(b) horizontally

Red is bent the most when it travels through a

(a) light pipe (optical fiber)

(b) prism

(c) grating

(c) grating

Two polaroids that have their polarization axes at 45o to each other will still allow light to pass through.

(a) True

(b) False

(a) True

The point where a soap bubble bursts will be black just as it bursts.

(a) True

(b) False

(a) True