Transcript 535/math practice 1-3 and 538/9,10

E-M Spectrum and Waves
Prentice Hall Chapter 18
Chapter Assignments
• Workbook and E-M Spectrum Activity
• Book
• Section 18.1: 535/math practice 1-3 and
538/9,10
• Section 18.2: 545/4, 5, &7
• Section 18.5: 562/3-7
• 565-67/1-10, 32-35, and FCAT practice
Review from the last chapter:
• Two types of waves are:
– Regarding requiring a medium for travel
• Mechanical and electromagnetic
– Electromagnetic does not require a medium
– Regarding shape of the wave
• Transverse and longitudinal
– Electromagnetic waves are transverse waves
Electromagnetic (E-M) Waves (LIGHT!)
Do not require a medium through which to travel
Light travels at 3.0 x 108 m/s in a vacuum or air
Its wavelength and frequency varies according to the type of E-M wave
Higher frequency 
Greater energy 
More penetration
The full range of frequencies of electromagnetic radiation is called the
electromagnetic spectrum.
Again, all of these forms move at 3.0 x 108 m/s in a vacuum (space) or air.
One type to the left of another type has a longer wavelength and a lower
frequency. For instance: radio waves have a longer wavelength than infrared.
Blue light has a higher frequency than red light.
Electromagnetic waves vary in wavelength and frequency
Properties of E-M Waves (Light)
• Light can act as a wave or a particle
• Only a very small portion of the E-M
Spectrum is visible to humans (between
infrared rays and ultraviolet rays)
• Those types to the right of the visible
portion are more penetrating and harmful
(can be used to “look inside” or pass
through objects); i.e., x rays and gamma
rays
c=fl
c=?
• This formula is used to determine
information about light.
• Let’s say that you know the wavelength of
yellow light is 600 x 10-7 m. What is its
frequency? Using c = f l
• f = c/ l
• f = 3.0 x 108 m/s / 600 x 10-7 m
• f = 3/600 x 108 + 7 = 0.005 x 1015
• f = 5 x 10-3 x 1015 = 5 x 10-3+15 = 5x1012 Hz
Another problem
• Find the frequency of an electromagnetic
wave in a vacuum with a wavelength of
0.02m
• f = c/ l
• f = 3.0 x 108 m / 0.02 m
• f = 1.5 x 1010 Hz
Assignment:
535/math practice 1-3 and 538/9,10
Behavior of Light
• Materials can affect the behavior of light
– Transparent materials allow most light to pass
through
– Translucent materials scatter light and makes
figures appear unclear in appearance
– Opaque materials either absorb or reflect all
of the light that hits them. No light can pass
through.
Interactions
• When light strikes a new medium, the light
can be reflected, absorbed, or transmitted.
When light is transmitted, it can be
refracted, polarized, or scattered.
Reflection
• When you look into a mirror, light reflects
from the mirror, and you see yourself
• Because of total internal reflection, laser
light can travel inside small glass (optical)
fibers and carry information
Refraction
• Bending of light as it passes from one
medium into another. It makes the pencil
look broken.
Newton and Prisms
• When white light passes through a prism
you see a rainbow, because of refraction:
• Different colors bend at different angles
• A rainbow is formed when water droplets
in the air disperse light.
Colors of objects
• Is dependent upon what the object is
made of and on the color of light that
strikes the object.
• See figure 24 (page 552) in your book
Primary Colors
Primary colors of light are Red, green, blue
Primary colors of
pigment are
Magenta, cyan,
and yellow
(See page 552
In your book)
Red, blue, and green light added
together produce white light.
R, blue, and green are primary
colors of light
Red plus green produce yellow, a
secondary color
Since yellow contains both red
and green, when you add yellow
to blue, you get white light!
What about cyan and red?
Since cyan contains green and
blue, when you add red, you get
white light again!
Mixing
• Mix colors of light together, you get more
light - additive process
*Mix complementary colors
of light  white light (blue
& yellow or green & magenta)
*Complementary colors
are opposite each other
in the color wheel.
• Mix colors of pigment together, you get
less light (it’s absorbed) - subtractive
process.
The primary colors
of pigment are the
secondary colors
of light!
Assignments:
• Section 18.2: 545/4, 5, &7
• Section 18.5:
562/3-7
• 565-67/1-10, 32-35, and FCAT practice
Other tidbits about light:
• Microwaves are used to communicate between
cell phones
• Light is produced in the filament of an
incandescent light bulb when electrons flow
through the filament
• Sodium-vapor lights are used for lighting many
streets and parking lots
• Fluorescent light tubes usually contain mercury
vapor (which give off invisible uv light causing
phosphors to emit visible light)
Light shining on objects
• See page 552
• What an object is made of and the color of
light that strikes it determine the apparent
color of the object.
• In white light all colors of the object are
evident
• When other colors of light shine on the
object, the colors appear very different.
Laser Light
• Laser stands for Light Amplification by
Stimulated Emission of Radiation.
• Laser light is coherent - all the waves have
the same: wavelength, direction, and
coincidental peaks. This means IT IS
VERY INTENSE & CAN BE HARMFUL!!!
Light - wave or particle?
• A wave when light interferes either
constructively or destructively
Light is turned “on” by
constructive interference
and “off” by destructive
interference resulting in an
interference pattern (shown
at left).
Light acts as a particle when…
• Electrons are emitted from a metal caused
by light striking the metal during the
PHOTOELECTRIC EFFECT
Examples:
Light sensors in cameras, video
cameras, automatic doors.
Newton said it acted as particles
because it travels in a straight line
and casts shadows.
Polarization
Only the blue waves can
pass through the opening in
the first card but not through
the 2nd card.
Infra- and Ultra• Infra- means under, so infrared light is
under red light (or to the left in the E-M
spectrum)
• Ultra- means above, so ultraviolet light is
above violet light (or to the right in the E-M
spectrum)
Sources
•
Frames 3 & 4
•
concise.britannica.com/ebc/art-70892/The-spec...
•
Frame 11
•
www.allrefer.com/pictures/s1/r0118400-refraction
•
Frame 11
•
•
•
hyperphysics.phy-astr.gsu.edu/.../refr2.html
Frame 12
http://www.physics.ohio-state.edu/~gilmore/images/collection/misc/prism.gif
•
www.britannica.com/eb/art-90651/A-prism-sprea...
•
•
Frame 13
www.fas.harvard.edu/.../ColorMixing06.jpg
Frame 17
hyperphysics.phy-astr.gsu.edu/.../lassol.html
Frame 18
http://abyss.uoregon.edu/~js/images/interference.gif
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