Chapter 29 Light Waves. Huygens’ Principle Every point on a wave front can be regarded as a new source of wavelets, which combine to produce the next.

Chapter 29

Light Waves

Huygens’ 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.

•Plane Waves

•Huygen’s Principle can be used to explain the propagation of wave fronts involved in reflection, refraction, and diffraction.

2. DIFFRACTION•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.

Double Slits

Single Slit

Diffraction Notes

•Long wavelengths bend a great deal around small objects.

•Because of diffraction AM radio waves may be received better 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. INTERFERENCE

•Two point sources

•Demo - Finger slit interference

•Demo - Single-Color Thin Film Interference

Soap Bubbles

Interference Colors by Reflection from Thin Films• Iridescence - the phenomenon of seeing colors by

interference in thin films.

•Demo - Soap bubbles and pipe

•Example - Coated photographic lenses

•Demo - Peacock feathers

• Interferometers measure small distances.

4. POLARIZATION•Common sources of light

are not polarized.•Polaroid Crystals - one axis

direction absorbs, one transmits.

•Polarized glare occurs on reflection from nonmetallic surfaces.

•Polarization Demo

COLORS BY TRANSMISSION THROUGH POLARIZING MATERIALS

Demo - Polaroids and accessories

•Sunglasses

Three-Dimensional Viewing

Stereoscopic viewers

Teapot Stereogram

5. HOLOGRAPHY

•Hologram means whole message.

•Demo - Reflection hologram

•Demo - Transmission hologram

•No lenses are used to create nor to view a hologram.

Holography Notes

•Object and source both illuminate all of the

photographic plate.

•The light used to make the hologram

must be coherent.

•A hologram is an interference pattern.

More Holography Notes

• It is best to use coherent light when viewing 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 Questions

(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

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

(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

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