Transcript Light Waves - Physics & Astronomy | SFASU

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.
Single Slit
Double Slits
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 l of light than was used in
creating the hologram.
Chapter 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
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
Polaroid sunglasses worn in a normal viewing
position will eliminate
polarized glare.
(a) vertically
(b) horizontally
(c) all
Two polaroids that have their polarization axes at
45o to each other will still allow light to pass
through.
(a) True
(b) False
The point where a soap bubble bursts will be
black just as it bursts.
(a) True
(b) False