I. Energy
• What is energy?
• Technically, energy
is the ability to do
work.
• It comes in many
forms and travels in
a particular way.
Types of Energy
• Two main types of
waves are mechanical
and electromagnetic.
• What is a wave?
• A wave is actually a
disturbance that
travels through
something from one
spot to another.
Different types of energy waves
• Movement within the
Earth's crust can cause
devastating seismic waves.
• Medical scientists use
ultrasound and other types
of waves to scan the inside
of the human body.
• Civil engineers need to
know how vibrations affect
buildings and other How do ultrasounds work? An instrument emits highfrequency sound, inaudible to human ears, and then records the
structures.
echoes as the sound waves bounce back to determine the size of
the object.
This information is used to produce images on a computer
screen.
A. Mechanical Waves
• 1. These need matter
to travel through.
• 2. Examples: water
waves, seismic waves,
and sound waves.
SOUND and the D word…
• 3. Sound travels
differently through
different mediums
(states of matter).
Which will it travel
best through? Why?
• It travels better
through denser objects
because the atoms are
close together.
B. Electromagnetic Waves
1. These do NOT need
matter to travel
through.
2. Remember: Rowdy
Martians in our
unusual x-ray game.
This is a silly phrase
to help you remember
all the EM waves.
C. How energy moves
1. Transverse waves move at
a right angle (electric field
moves at a right angle to
the magnetic field).
• a. Light is an example.
• b. The wave people create
in a ball game is another
example.
• c. The movement of a
guitar string is another
example.
• See animated pictures @
• http://www.acs.psu.edu/dr
ussell/Demos/waves/wave
motion.html
2. Longitudinal (compressional)
waves
• a. These move in a
back and forth motion.
• b. Sound waves are an
example.
• c. Slinky waves and
alternating current
electricity are other
examples.
3. Combinations:
• Water moves in both ways (transverse and
longitudinal) forming a circular pattern.
• a. Example: when you drop a stone in a
pool, the waves move outward. The water
molecules actually move in a circular
pattern (combination of transverse and
longitudinal)/
Traveling faster than the speed of
sound…is supersonic!
• Shock waves are the primary reason you hear what's called a sonic
boom.
• Picture an airplane flying through the air. As the airplane moves, it
pushes air molecules out of its way, continuously creating waves of
compressed and uncompressed air. These air pressure waves move
away from the airplane in all directions at the speed of sound (imagine
ripples that form by dropping a pebble in a pond.)
Next, break the sound barrier by increasing the airplane's speed to
supersonic, or faster than the speed of sound. When the airplane moves
at supersonic speeds, the air pressure waves begin to pile up ahead of
the airplane and compress, forming shock waves. (These are similar to
a "bow wave" that piles up at the front of a boat as it moves through
water.)
You can see the
sonic boom
cloud as the jet
breaks the
sound barrier.
• The space shuttle
produced sonic booms
as it left the Earth’s
atmosphere. So does
lightning (thunder is a
sonic boom).
II.The Electromagnetic Spectrum:
From the largest wave to smallest wave
A. Radio waves are the
largest waves (cell
phones, cable TV &
satellite TV, radio,
telescopes).
97.5 megahertz
• Frequency is the number
of cycles of a wave to pass
a given point in one
second.
• Measured in units called
hertz.
• 97.5 as a place on the FM
dial means that the radio
waves are traveling 97.5
million cycles per second.
Can you hear me now???
• James Clerk Maxwell
predicted the existence of radio
waves in the 1860’s. In 1886,
German physicist, Heinrich
Hertz proved the existence of
radio waves.
• He used a spark gap attached to
an induction coil and a separate
spark gap on a receiving
antenna.
• When waves created by the
sparks of the coil transmitter
were picked up by the receiving
antenna, sparks would jump its
gap as well.
Guglielmo Marconi
was the first
to send a wireless signal
(using a telegraph) in
1895, but
Nikola Tesla was the first
to patent it.
In 1932, Karl Jansky at
Bell Labs revealed that
stars and other objects in
space radiated radio
waves.
Satellite Radio
• Satellite works very much like regular radio
waves, it just has a wider band (more
stations) and is able to broadcast over a
larger area.
• Both types use receivers and convert the
signal to mechanical vibrations in the
speaker to create the sound waves you can
hear.
Astronomical objects that have a changing magnetic field can produce radio waves.
Data pictured below show emissions from a variety of sources including radio bursts from the Sun, the
Earth, and even from Jupiter's ionosphere whose wavelengths measure about fifteen meters in length. The
far right of this graph shows radio bursts from the Sun caused by electrons that have been ejected into
space during solar flares moving at 20% of the speed of light
Microwaves
• B. Microwaves are
used in ovens, radar,
Doppler radar, and
satellites.
The first microwaves didn’t
cook!
•
•
•
•
During World War II, two
scientists invented the magnetron, a
tube that produces microwaves.
Installing magnetrons in Britain’s
radar system, the microwaves were
able to spot Nazi warplanes on
their way to bomb the British Isles.
In the 1950’s, Percy Spencer
accidentally found that these
microwaves had melted a candy bar
in his pocket.
Experiments showed that
microwave heating could raise the
internal temperature of many foods
far more rapidly than a
conventional oven.
• The first microwave ovens were
so large (refrigerator size) that
most people didn’t own one.
• It was the discovery of their
reaction to metals that led to the
invention of radar.
Infrared Waves
• C. Examples of infrared waves
•
•
include heat, sun, tv remotes, and
some satellites.
In 1800, William Herschel
conducted an experiment
measuring the difference in
temperature between the colors in
the visible spectrum.
He noticed an even warmer
temperature measurement just
beyond the red end of the visible
spectrum, Herschel had discovered
infrared light.
D. Optical Light
1. Roy G. Biv
2. From longest to
shortest: red, orange,
yellow, green, blue,
indigo, violet.
• All colors are in white
light.
• We use lenses to help
us see: convex (in our
eyes) and concave.
LIGHT!
• Isaac Newton's
experiment in 1665
showed that a prism
bends visible light and
that each color refracts
at a slightly different
angle depending on
the wavelength of the
color.
• Many folks tried to
say that something
carried light. They
even named this
something
luminiferous aether.
Later scientists,
including Einstein,
will go on to prove
this is not true.
How light moves…
• When a light wave encounters an object, it may
be reflected,
absorbed,
refracted,
polarized,
diffracted,
or scattered depending on the composition of the
object and the wavelength of the light.
Ultraviolet Rays
• E. UV rays come from the Sun.
• In 1801, Johann Ritter
conducted an experiment to
investigate the existence of
energy beyond the violet end of
the visible spectrum.
• Knowing that photographic
paper would turn black more
rapidly in blue light than in red
light, he exposed the paper to
light beyond violet. Sure
enough, the paper turned black,
proving the existence of
ultraviolet light.
F. X-rays
• X-rays were named as
such because the
scientist who
discovered them did
not know what to call
them.
• So, he called them
“x-rays.”
Wilhelm Roentgen x-rays his
wife’s hand in 1895.
•
•
•
Roentgen discovered that firing
streams of x-rays through the body
created images of the bones inside.
When you get an x-ray taken, x-ray
sensitive film is put on one side of
your body, and x-rays are shot
through you.
Because bones are dense and
absorb more x-rays than skin does,
shadows of the bones are left on the
x-ray film while the skin appears
transparent.
Gamma rays
• G. Gamma rays are
the smallest waves on
the spectrum.
• They are used to kill
cancer cells.
Henri Becquerel discovers
gamma radiation.
•
•
•
In 1896, French scientist Henri
Becquerel discovered natural
radioactivity.
Many scientists of the period were
working with cathode rays, and
other scientists were gathering
evidence on the theory that the
atom could be subdivided.
Some of the new research showed
that certain types of atoms
disintegrate by themselves.
•
•
•
•
Henri Becquerel discovered this
while investigating the properties
of fluorescent minerals.
One of the minerals Becquerel
worked with was a uranium
compound.
Uranium ore produces naturally
occurring gamma radiation.
The Curies will go on to work with
gamma radiation further.