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Electromagnetic Waves and Light
Table of Contents
The Nature of Electromagnetic Waves
Waves of the Electromagnetic Spectrum
Light and Color
Reflection and Mirrors
Refraction and Lenses
The Electromagnetic Spectrum
What makes up an electromagnetic wave?
• An electromagnetic wave is a transverse wave
that involves the transfer of electric and
magnetic energy.
• It is made up of vibrating electric and magnetic
fields that move through space or some
medium at the speed of light.
The Nature of Electromagnetic Waves
Electromagnetic Wave
An electromagnetic wave travels through space at the speed of light—
about 300,000 kilometers per second.
What models explain how electromagnetic
waves behave?
Is light a particle or a wave?
Wave Model of Light:
• An ordinary beam of light consists of waves that vibrate
in all directions.
• A polarizing filter acts as though it has tiny slits aligned
in only one direction, either horizontal or vertical,
allowing only some waves to pass through.
• The light that passes through is called polarized light.
• Simple Explanation of Polarised Lenses
The Nature of Electromagnetic Waves
Light as a Wave
A polarizing filter acts like the slits in a fence.
Particle Model of Light:
• When a beam of high frequency light shines on some
metals, electrons move.
• Sometimes it moves so much that it is knocked out of
the metal and is called the photoelectric effect.
• Light can be thought of as tiny a particle of energy called
a photon, that contains enough energy to knock an
electron free from the metal.
• A Level Physics - The Photon
The Nature of Electromagnetic Waves
The Photoelectric Effect
Photons hitting a metal
surface knock out
electrons.
Electromagnetism : Documentary on How the
Electromagnetic Spectrum Works (Full
Documentary)
How do electromagnetic waves
compare?
• All electromagnetic waves travel at the same speed
in a vacuum.
• A vacuum is space without any gas.
• They have different wavelengths and different
frequencies.
• Visible light is the only light we can see.
• As wavelength decreases, the frequency
increases, so waves with the shortest
wavelengths have the highest frequencies.
• The higher the frequency of a wave, the higher
its energy.
• Complete pg 405
Waves of the Electromagnetic Spectrum
Comparing Electromagnetic Waves
Different types of electromagnetic waves have different
wavelengths. Which are the visible light, radio waves, and Xrays?
What makes up the EM
spectrum?
• Radio Waves:
• EM waves with the longest wavelengths and
lowest frequencies are radio waves.
• Radio waves are used to carry signals at
certain frequencies.
• Complete pg 406
Waves of the Electromagnetic Spectrum
The Electromagnetic Spectrum
The electromagnetic spectrum can be broken up into different categories. Use the
word bank to complete the boxes in the diagram.
• Microwaves:
• Microwaves have a higher frequency than radio waves.
• Besides heating up food, microwaves are useful in radar
and cellular phones.
• Radar (radio detecting and ranging) uses reflected
microwaves to detect objects.
• Distance: by measuring the time it takes for the signal
to return, the distance between objects can be
determined.
• Speed: by using the Doppler effect, the change in the
frequency of the reflective waves from the original
waves determines the speed of the moving object.
• Complete pg 407
Infrared Rays:
• Infrared rays have higher frequencies than microwaves, so
have more energy.
• The invisible heat that we feel is infrared radiation or rays.
• Heat lamps have bulbs that give off mainly infrared rays.
• Warmer objects give off infrared rays with more energy and
higher frequencies than cooler objects.
• A thermogram is an image that shows different
temperatures with different colors.
• Complete pg 408
Visible Light:
• Visible light are the only waves we can see with our eyes
and make up only a small part of the EM spectrum.
• The white light is actually a mixture of many colors based
on their wavelengths.
Ultraviolet Light:
• Since ultraviolet rays have higher frequencies than visible
light, they carry more energy.
• Too much UV can damage cells, especially skin cells, but
small doses are useful for skin to produce vitamin D.
• Complete pg 409
X-rays:
• Because of their high frequencies, X-rays carry more
energy than UV rays and can penetrate most matter.
• Dense matter absorb X-rays, so they do not pass through.
• X-rays are useful in seeing cracks in dense material such
as bone, teeth, steel, or concrete.
• Too much exposure to X-rays can be harmful.
Gamma rays:
• Since they have the greatest amount of energy, gamma
rays are the most penetrating of EM waves.
• Gamma rays are helpful in examining the body’s internal
structures.
• Some radioactive substances and certain nuclear reactions
produce gamma rays.
• Complete pg 410-411
Waves of the Electromagnetic Spectrum
Types of Waves
The electromagnetic spectrum includes many kinds
of waves. Identify each kind of wave on the electromagnetic
spectrum. What is the name of the highest energy waves?
What determines color?
• When light strikes an object, the light can be reflected,
transmitted, or absorbed.
• Most materials can be classified as transparent,
translucent, or opaque based on what happens to light
that strikes the material.
• Light can pass through a transparent material
without being scattered, so you can see clearly what
is on the other side.
• A translucent material scatters the light that passes
through it, so you can see an object, but the details
are blurred.
• A material that reflects or absorbs all of the light that
strikes it is called opaque, so you cannot see
through it because light cannot pass through it.
Complete pg 413
Light and Color
Types of Materials
Suppose the ball was placed behind the three-sectional window below.
Then, what would you see inside the dashed circle?
• Opaque objects:
• The color of an opaque object depends on the
wavelengths of light that the object reflects.
• Every opaque object absorbs some wavelengths of light
and reflects others.
• Transparent & translucent objects:
• Materials that are transparent or translucent allow only
certain colors of light to pass through them.
• They reflect or absorb the other colors.
• A color filter allows only certain wavelengths to pass
through, allowing only certain color of light to pass through.
• Complete pg 414-415
Light and Color
Color of an Opaque Object
The color an apple appears to be depends on the color of the light that
strikes it.
Light and Color
Color Filters
Imagine looking at the beach
ball through a red, green, or
blue filter. How will each
section of the beach ball
appear?
How do colors combine?
• Primary colors of light are red, green, and blue (not the
same as primary colors in art).
• When the three colors of light are combined in equal
amounts, they produce white light.
• If colors are combined in unequal amounts, they produce a
secondary color, such as yellow, cyan, or magenta.
• Any two colors (a secondary and primary) that combine to
form white light are called complementary colors.
• Complete pg 416
Light and Color
Primary Colors of Light
The primary colors of light are red,
green, and blue. Combined in different
amounts, the primary colors can
produce other colors.
• Artists use pigments to absorb some colors and reflect
others to produce shades of colors.
• As pigments are added together, fewer colors of light
are reflected and more are absorbed. The more
pigments that are combined, the darker the mixture
looks.
• Cyan, yellow, and magenta (Ever wonder why these 3
colors are used in printer ink?) are the primary colors
of pigments. When these 3 colors are combined, black
is produced.
• Complete pg 417
Light and Color
Primary Colors of Pigment
When the three primary colors of pigments are combined in equal amounts,
they produce black.
What are the kinds of reflection?
• To show how light reflects, you can represent light
waves as straight lines called rays.
• Light obeys the law of reflection- the angle of
reflection equals the angle of incidence.
Regular Reflection
• Regular reflection occurs when parallel rays of light hit
a smooth surface.
• All of the light rays reflect at the same angle so you
see a clear image.
• Shiny surfaces produce regular reflection.
Diffuse Reflection
• Diffuse reflection occurs when parallel rays of light hit
an uneven surface.
• Each light ray obeys the law of reflection but hits the
surface at a different angle so each ray reflects at a
different angle.
• You either don’t see an image or the image is not
clear because the surface is not smooth.
• Even if it looks smooth, there are small bumps that
reflect light at different angles.
• Complete pg 419
Reflection and Mirrors
Diffuse and Regular Reflection
Which kind of reflection occurs on each surface?
What types of images do mirrors produce?
Plane Mirror:
• A plane mirror is a flat sheet of glass that has a
smooth, silver-colored coating on one side.
• When light strikes a mirror, the coating reflects the
light creating a virtual image.
• The image is virtual since it appears to be behind the
mirror, but it really isn’t there.
• The image is not quite the same as the object since
the left and right are reversed.
• A plane mirror produces a virtual image that is upright
and the same size as the object.
Concave Mirror
• A mirror with a surface that curves inward, like a bowl, is a
concave mirror.
• Rays of light are parallel to the optical axis, an imaginary
line that divides the mirror in half.
• Concave mirrors reflect the parallel rays of light so that
they meet at a point, called the focal point.
Reflection and Mirrors
Concave Mirror
A concave mirror reflects rays of light parallel to the optical axis back
through the focal point.
Concave Mirrors
• The type of image that is formed depends on the location of the
object.
• If the object is farther away from the mirror than the focal point,
the reflected rays form a real image.
• A real image can be projected on a surface but it is upside down
although it can be smaller, larger, or the same size as the object.
• If the object is between the mirror and the focal point, the
reflected rays form a virtual image that is larger than the object.
• Concave mirrors produce magnified images.
• Complete pg 421
Reflection and Mirrors
Real and Virtual Images
The figures show how a
concave mirror can produce
both real and virtual images.
Convex Mirrors
• A mirror with a surface that curves outward is called a
convex mirror.
• The reflected rays spread out the parallel rays of light
but appear to come from a focal point behind the
mirror.
• A convex mirror produces a virtual image that is
always smaller than the object.
• Convex mirrors are used in cars to allow you to see a
larger area that you could with a plane mirror, but the
image is reduced in size and appears to be farther
away than it really is.
• Complete pg 422
Reflection and Mirrors
Convex Mirror
Light rays parallel to the optical axis reflect as if they came from the
focal point behind a convex mirror. Where do two reflected rays
intersect behind the mirror?
Reflection and Mirrors
Different Types of Images Formed by Mirrors
Complete pg 423
What causes light to bend?
• Refraction can cause you to see something that may
not actually be there.
• Light will bend each time it passes through a different
medium such as water, glass, and air.
• When light rays eneter a new medium at an angle, the
change is speed causes the rays to bend.
• Complete pg 425
Refraction and Lenses
Optical Illusion In a
Fish Tank
There is only one fish
in
the tank, but
refraction
makes it look
as though there are
two.
Refraction in different mediums
• Some mediums cause light to bend more than others.
• Light travels fastest in air and slows as it passes
through other mediums.
• Glass causes light to bend more than either air or
water does so it has a higher index of refraction, the
measurement of how much a light ray bends when it
enters than medium.
Refraction and Lenses
Refraction of Light
The light ray bends
as it passes through different
mediums.
Refraction and Lenses
Bending Light
The table shows the
index of refraction of
some common mediums.
Complete pg 426
Prisms and rainbows
• When white light enters a prism, each wavelength is
refracted by a different amount causing white light to
spread out into the colors of the spectrum.
• The same process occurs in water droplets
suspended in the air.
• These water droplets act like tiny prisms and create a
rainbow.
• Complete pg 427
Refraction and Lenses
Rainbow
A rainbow forms when light is reflected and refracted by
water droplets suspended in the air.
Mirages
• Mirage is an image of a distant object caused by refraction
of light.
• The puddles are light rays from the sky that are refracted
to your eyes.
• The air just above the land is hotter than the air higher up.
• Light travels faster in hot air, and the light from an object
traveling towards the ground are bent upward by the hot
air.
• Our brain assumes that these rays traveled in a straight
line so they look like they reflected off of a smooth
surface.
• Complete pg 428
What determines the type of image formed
by a lens?
• A lens is a curved piece of glass that refracts light and
forms an images by refracting light rays that pass
through it.
• A concave lens is thinner in the center. Light rays bend
away from the optical axis and never meet creating
only virtual images that are upright and smaller than
the object.
Refraction and Lenses
Concave Lens
A concave lens produces a
virtual image that is upright
and smaller than the object.
In the second diagram,
where would the image be
when the two light rays are
extended back to
the same side of
the lens as the object?
• A convex lens is thicker at the center. Light rays bend
towards the center of the lens. The more curved the
lens, the more it refracts light.
• When an object is between the lends and the focal
point, the refracted rays form a virtual image on the
same side of the lens and is larger than the object.
• When the object is outside of the focal point, the
refracted rays form an upside down, real image on
the other side of the lens that can be smaller, larger,
or same size.
Refraction and Lenses
How a Convex
Lens Works
The type of image
formed by a convex
lens depends on the
object’s position.
Which image is
virtual and which is
real?
Complete pg 431
Refraction and Lenses
Lenses and Mirrors
These photos show parallel rays of light
passing through a convex lens and a
concave lens. How would you complete
the Lenses and Mirrors table?