Download Chapter 22: Light

Chapter 22: Light
What is light?
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It is an electromagnetic wave (EM
wave).
Does not require a medium to travel
Consists of changing electric and
magnetic fields (fields are forces that
push and pull on another object
without touching it)
Why are EM waves really
transverse waves?
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The electric and magnetic fields travel
at right angles to each other (in other
words they are perpendicular to one
another)
And the fields travel perpendicular to
the direction of the motion
How are EM waves
produced?
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By the vibration of an electrically charged
particle
When the electron absorbs energy it will
jump orbital levels
Eventually, the e will move back down
releasing a burst of energy called a photon
The constant stream of photons create the
EM waves and it is called radiation.
How do you calculate the
speed of light?
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Through a vacuum (in space- not Hoover),
light travels about 300,000,000 m/s
Light travels slightly slower through air,
glass, and other types of matter
Light travels more than 880,000 times faster
than sound
Tidbit: if you could run as fast as light, you
will circle the Earth 7.5 times in 1 sec.
Math Break
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1.
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Speed = distance / time
Time = distance / speed
EX: time = 382,000,000 m / 300,000,000
m/s
Time = 1.27 s
You try this: The earth is 150,000,000,000
m from the sun. How long does it take for
the light to travel that distance?
500 s or 8.3 mins.
What is the EM
Spectrum?
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It consists of all parts of light.
Each type of EM wave has different
wavelengths and frequencies.
However, they all still travel about the
same speed.
Categories of the EM
Spectrum
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2.
3.
4.
5.
6.
7.
From longest wavelength to shortest
wavelength
Radio
Microwaves
Infrared
Visible Light
Ultraviolet
X-rays
Gamma Rays
EM Spectrum
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The long wavelengths have low
frequency.
The short wavelengths have high
frequency.
But they all travel at the same speed.
Radio Waves
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1.
2.
2 types: AM and FM
AM (means amplitude
modulation) can
travel longer, but
hold smaller amounts
of info
FM (means frequency
modulation) travel
shorter, but hold a
bunch of info and
sound better
Radio Waves
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Useful for: astronomy, talk shows,
telescopes, music
Microwaves
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Shorter wavelengths than radio, but
higher frequencies
Part of radar, cell phones, microwave
ovens
Harmful at high intensities: can kill
living cells.
Infrared
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2 types: thermal and near
Uses: heating food, fiber optics, lasers,
and our bodies
Visible Light
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The only light our eyes can detect
without special equipment
Roy G Biv
Generally, harmless
Ultraviolet (UV)
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Produced mostly by the sun; however,
can be found in black lights, tanning
beds
Harmful: can lead to cancer from
overexposure
X-ray
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Used for space observations, medical
diagnosis
Harmful: can mutate DNA, can cause
cancer
Gamma Rays
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Smallest wavelength and highest
frequency
Used for medical treatments, detecting
radioactivity and nuclear weapon
explosions
Harmful: cancer
Interactions of Light
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Light can reflect, refract, be absorbed,
be scattered, diffract, and interference
Reflection
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The bouncing back of a wave when it
strikes a surface
Law of Reflection states that the angle
of incidence is equal to the angle of
reflection.
2 types: regular reflection and diffused
reflection
Types of Reflection
– A regular reflection is the striking of
light rays at the same time. It is off a
smooth surface. (Think of a ball
bouncing off the pavement)
– A diffuse reflection is the striking of light
rays at uneven time. It is off a bumpy
surface. The light rays bounce in
different directions. (Think of a ball
bouncing off an uneven surface)
Law of Reflection
Absorption
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The transfer of light energy to particles of
matter
the frequency of the incoming light wave is
at or near the energy levels of the electrons
in the matter. The electrons will absorb the
energy of the light wave and change their
energy state.
Scattering
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The release of light energy by particles
of matter that have absorbed energy
Refraction
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The bending of light wave as it passes
as an angle from one medium to the
next
Bends due to the change of speed of
light through the different media
Creates the rainbow, optical illusions
Optical Illusions
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How your brain interprets the light
waves traveling
Follow the pink dots and
they remain pink; stare at
the black center and they
become green
Find the man’s face
Is this picture moving?
Rabbit or Duck?
Can you count the black
dots?
Diffraction
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Light can diffract.
However, it can only diffract around
smaller objects.
The outside of the light gets fuzzy
when diffracting.
Interference
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Does happen
Can see constructive interference
Destructive interference is very rare