Download Light: An Electromagnetic Wave

Bellringer
What do you think light is? Is light made of matter?
Can light travel through space?
Explain your answers in your lab journal.
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Light: An Electromagnetic Wave
• Light is a type of energy that travels as a wave. But
unlike most other types of waves, light does not
require matter through which to travel.
• An electromagnetic wave is a
wave that consists of electric and
magnetic fields that vibrate at right
angles to each other.
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Radiation
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Radiation is the transfer of energy as
an electromagnetic wave.
Electromagnetic waves are different
because they can travel through
space.
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How are EM produced?
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Electromagnetic waves can be
produced by a vibrating, electrically
charged particle.
When the particle vibrates, the electric
field around it vibrates, too. The
vibration of the electric field creates a
vibrating magnetic field. The vibration
of the two fields together produce an
EM wave.
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Speed of Light
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299,792.458 km/s or 300,000 km/s
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Remember s = d/t
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Visible Light
• Visible Light from the Sun Visible light is the very
narrow range of wavelengths and frequencies in the EM
spectrum that humans eyes respond to. Visible
light
waves have wavelengths between 400 nm
and 700 nm.
•Important because it supplies all of the
energy on Earth.
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White Light
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White light is visible light of all
wavelengths combined.
– Sources of white light include the sun,
incandescent light bulbs, and fluorescent
light bulbs.
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Visible Light, continued
• Colors of Light Humans see different wavelengths
of visible light as different colors. The longest wavelengths are seen as red light. The shortest wavelengths are seen as violet light.
• The range of colors is called the visible spectrum.
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Electromagnetic
Spectrum
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The electromagnetic spectrum is made
up of electromagnetic waves of all
wavelengths.
Infrared light has the longest
wavelength, visible light has the next
longest, and ultraviolet light has the
shortest wavelength.
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Radio Waves
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Radio waves can transmit information
by varying the waves’ amplitude
(called amplitude modulation) or by
varying the waves’ frequency (called
frequency modulation).
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UV Waves
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UV light is useful because it can kill
bacteria and help the human body
produce vitamin D.
But overexposure to UV light can
cause sunburn and skin cancer.
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X-Rays and Gamma Rays
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X rays and gamma rays are used in
medicine to check for broken bones
and to treat cancer. But X rays and
gamma rays can also kill healthy,
living cells.
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Microwaves
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Used in radar guns
Used to cook food.
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Reflection
• Reflection happens when light waves
bounce off an object. Light reflects off
objects all around you.
• The Law of Reflection states that the
angle of incidence is equal to the angle
of reflection.
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Types of Reflection
•You see your image in a mirror
because of regular reflection.
• Regular reflection happens when light
reflects off a very smooth surface. All
the light beams bouncing off a smooth
surface are reflected at the same angle.
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Reflection, continued
• You cannot see your image in a wall
because of diffuse reflection.
• Diffuse reflection happens when light
reflects off a rough surface, such as a
wall. Light beams that hit a rough
surface reflect at many different angles.
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Reflection, continued
• Light Source or Reflection? The tail of a firefly,
flames, light bulbs, and the sun are light sources. You
can see a light source in the dark because its light
passes directly into your eyes.
• Most things around you are not light sources. But
you can see them because light from light sources
reflects off the objects and the travels to your eyes.
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Absorption and Scattering
• Absorption of Light The transfer of energy carried
by light waves is called absorption.
• When a beam of light shines through the air, particles
in the air absorb some of the light’s energy. As a result,
the beam of light becomes dim.
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Absorption and Scattering, continued
• Scattering An interaction of light with
matter that causes light to change
direction is scattering. Light scatters in all
directions after colliding with particles of
matter.
• Light can be scattered out of a beam by air particles.
This scattered light allows you to see things outside of
the beam. But, the beam becomes dimmer because light
is scattered out of it.
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Refraction
• Refraction
is the bending of a wave as
it passes at an angle from one material
to another.
• Refraction of light waves occurs because the
speed of light varies depending on the material
through which the waves are traveling.
•When a wave enters a new material at an angle,
the part of the wave that enters first begins
traveling at a different speed from that of the rest
of the wave.
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Refraction, continued
• A lens is a transparent object that refracts
light to form an image.
• Convex lenses are thicker in the middle
than at the edges.
•When light beams pass through a convex lens, the
beams are refracted toward each other.
• Concave
lenses are thinner in the middle
than at the edges.
•When light beams pass through a concave lens, the
beams are refracted away from each other.
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Refraction, continued
• Refraction and Optical Illusions Your brain
always interprets light as traveling in straight lines.
• But when you look an an object that is underwater,
the light reflecting off the object does not travel in a
straight line. Instead, it refracts.
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Refraction, continued
• Because of refraction, the cat and the fish see
optical illusions.
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Refraction, continued
• Refraction and Color Separation White light is
composed of all the wavelengths of visible light. The
different wavelengths of visible light are seen by
humans as different colors.
• When white light is refracted, the amount that the
light bends depends on its wavelength.
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Refraction, continued
• Waves with short wavelengths bend more than
waves with long wavelengths.
• White light can be separated into different colors
during refraction, as shown below.
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Chapter O3
Diffraction
• Diffraction
is the bending of waves
around barriers or through openings.
• The amount a wave diffracts depends on its
wavelength and the size of the barrier or opening.
• The greatest amount of diffraction occurs when the
barrier or opening is the same size or smaller than
the wavelength.
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Diffraction, continued
• Diffraction and Wavelength The wavelength of
visible light is very small.
• So, a visible light wave cannot diffract very much
unless it passes through a narrow opening, around
sharp edges, or around a small barrier.
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Interference
• Interference is a wave interaction that
happens when two or more waves overlap.
• Constructive Interference happens when
waves combine to form a wave that has a
greater amplitude than the original waves had.
• Destructive Interference happens when
waves combine to form a wave that has a
smaller amplitude than the original waves had.
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Interference, continued
• The image below shows what happens when light
combines by interference.
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Light and Matter
• When light strikes any form of matter, it can be reflected,
absorbed, or transmitted.
• Reflection
happens when light bounces off
an object.
• Absorption is the transfer of light energy to
matter.
• Transmission is the passing of light
through matter.
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Light and Matter, continued
• Transparent is matter through which light
is easily transmitted. Glass is transparent.
• Translucent matter transmits light but also
scatters it. Frosted windows are translucent.
• Opaque matter does not transmit any light.
Computers and books are opaque.
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Light and Matter, continued
• The images below explain the difference between
the terms transparent, translucent, and opaque.
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Colors of Objects
• Humans see different wavelengths of light as
different colors.
• The color that an object appears to be is determined
by the wavelengths of light that reach your eyes.
• Light reaches your eyes after being reflected off an
object or after being transmitted through an object.
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Colors of Objects, continued
• Colors of Opaque Objects When white light strikes
a colored opaque object, some colors of light are
absorbed, and some are reflected.
• Only the light that is reflected reaches your eyes and
is detected. So, the colors of light that are reflected by
an opaque object determine the color you see.
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Colors of Objects, continued
• Colors of Transparent and Translucent Objects
Ordinary window glass is colorless in white light
because it transmits all the colors of light that strike it.
But some transparent objects are colored.
• When you look through colored transparent or
translucent objects, you see the color of light that was
transmitted through the material.
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Mixing Colors of Light
• Red, blue, and green are the primary colors of light. These
three colors can be combined in different ratios to produce
white light and many colors of light.
• Color
Addition is combining colors of light.
• Light and Color Television The colors on a color TV are
produced by color addition of the primary colors of light.
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Mixing Colors of Pigment
• Pigments and Color A material that gives a
substance its color by absorbing some colors of light
and reflecting others is a pigment.
• Color Subtraction When you mix
pigments together, more colors of light
are absorbed or taken away. So, mixing
pigments is called color subtraction.
• Yellow, cyan, and magenta are the primary pigments.
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