Download Electromagnetic Radiation

Electromagnetic Radiation
Chapter22
Electromagnetic Radiation
• Traveling oscillation of the electromagnetic
field
Electromagnetic Radiation
• Includes all waves that travel at the speed of
light:
Electromagnetic Spectrum
• Gamma Rays – highest energy
• Ultraviolet light (UV) – mostly blocked by the
atmosphere (sunburn)
• Visible light – ROYGBIV
• Infrared (IR) – thermal imaging
• Microwaves – texting
• Radio – communication with man-made
satellites
Uses of EM in our world
• What do a PET scanner, a mobile phone, ear
thermometer and a microwave oven have in
common?
• PET is gamma rays, thermometer is IR, oven
and mobile phone are microwaves.
Fiber Optics
• Utilize IR and visible light which can travel
faster
• Focuses on the particle component of light
(photon)
• Light enters the optical fiber and utilizes total
internal reflection to be able to reach the far
end of the tube
Visible Light (white light)
• Red
• Orange
• Yellow
• Green
• Blue
• Violet
Longest wavelength, lowest frequency and
lowest energy
Shortest wavelength, higher frequency and
highest energy
Dispersion
• Separating light into its wavelength
• White light is separated into the colors of
visible light.
How is a Rainbow formed?
• Water droplets act like prisms and disperse
the white light
• Different colors come from different water
droplets
• Red light is not bent as much, so it is on top of
a rainbow.
Why is the sky blue?
• Blue light gets scattered more frequently than
the other colors because the wavelength is
shorter
• Air molecules in the atmosphere scatter the
high frequency light waves which are violet
and blue
• We see blue because our eyes
are more sensitive to blue
Why are sunsets red?
• Air molecules in atmospheric scatter blue, so
mainly RED frequencies make it through
• At dawn and sunset, the sunlight must go
through more atmosphere, so the red end
which has longer wavelengths can reach us.
• So we see red at
sunrise and sunset
Why are the clouds white?
• Clouds are made of different size water
droplets, so all frequencies of light get
scattered equally making the clouds appear
white.
Why is the ocean blue/green?
• Water absorbs red, orange and yellow and
turns them into heat leaving only green and
blue to be reflected
• So the ocean looks
cyan or blue/green
Different Ways of Seeing Color
Color by Reflection
Color by Transmission
Color by Addition
Color by Subtraction
Color by Reflection
• Pigments
– Absorb some wavelengths of light and reflect
others
Color by Transmission
• White reflects all wavelengths
• Black absorbs all wavelengths
• The color of the object depends on the color
of light it transmits.
Seeing Color
• The color an object appears depends on the
colors of light it reflects.
For example, a red book only reflects red light:
Only red light
is reflected
Color by Addition
• Adding the wavelengths of light
• Additive primary colors: red, green and blue
• Color TV is based on seeing these 3 colors and
the combination of them
Color by Subtraction
• Mixing colored pigments (used in paint)
• Used in printing illustrations
• 3 paint or dye colors used: magenta (bluish
red), yellow and cyan (greenish blue)
Additive and Subtractive