Transcript Chapter 17

Chapter 17 - Light
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An electromagnetic wave is composed of
electric and magnetic fields that are
vibrating perpendicular to each other.
What is polarized light?
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When light goes through a polarized filter only
vibrations of one direction are allowed through.
Polarized light – light that is vibrating only in one
direction.
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Light acts like both a
particle and a wave
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Photoelectric effect –
when light “particles”
knock electrons off of
a surface.
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Photon – a particle of
light
Radio waves – generated and absorbed by electrons pulsing
back and forth along a wire (low energy wave)
Long infrared waves – used in some communications (cell phones)
Short infrared (heat waves) – produced and absorbed by
molecular vibrations, produced in microwave ovens.
Visible light – created and absorbed by electrons dropping down
energy levels. The difference in energy of the energy levels
corresponds to the wavelength of light emitted.
Ultraviolet light – (beyond violet) (black light) cause sunburn and
skin cancer, helps skin provide vitamin D
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X-rays – penetrated the body, absorbed by dense tissue
(bone). Will darken a photographic plate.
Gamma rays – comes from all regions of space, like tiny
bullets passing through body. Used to help treat cancer.
All electromagnetic waves travel the
same speed but they all have different
frequency and wavelength.
 What is the relationship between
wavelength and frequency?
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The higher the frequency, the shorter the
wavelength
 The lower the frequency, the longer the
wavelength.
 The longer the wavelength the lower the energy
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What is radar? How does radar work?
Radio detection and ranging is done by
sending a pulse of radio waves. The
time it takes for them to return gives the
distance to the object.
The change in frequency as the waves
bounce off the object can be used to
determine how fast the object is going.
The police radar gun uses the Doppler
effect to determine your speed.
What is Magnetic
Resonance Imaging (MRI)?
 A short burst of radio
waves, along with a strong
magnetic field cause a
person’s atoms to line up
with the magnetic field.
 The atoms return to a
random arrangement at
different rates and this is
used to give an image of
soft tissues such as the
brain.
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Infrared rays and thermograms
 Infrared cameras and thermograms
allow us to see heat radiation. One
application is determining areas of
greatest heat loss in homes.
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Incandescent light
 Incandescent lights have a tungsten
filament that gets “white hot”
 Most of the energy given off is heat
radiation (less than 10% efficient)
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How do fluorescent lights work?
Ultraviolet light is created as an electric
current passes through a vapor
The inside of the light is coated with a
phosphor which glows when hit with U.V. light
They are more efficient than incandescent lights.
Sea shells under black fluorescent light
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Bioluminescence – what is it?
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A chemical reaction within an organism
produces light (firefly).
Artificial bioluminescence
created by genetic
engineering in a tobacco
plant
AM and FM waves, what are they?
How are they different?
A.M. : Amplitude modulation – the amplitude
of a wave is changed to carry information.
 F.M. : Frequency modulation – the
frequency is modulated to carry information.
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