Transcript microwaves - TeacherWeb

Electromagnetic Spectrum
Low Energy
Low Frequency
High Wavelength
High Energy
High Frequency
Low Wavelength
Radio Waves
low energy, low frequency, high wavelength
• Can be heard by elephants
• Sound made by Earth as it
“hums” may be from storms
• AM waves bounce off
ionosphere (part of our
atmosphere) so they can be
heard far away from the
transmitter
• FM waves don’t bounce so
the signal weakens with
distance from the transmitter
Microwave
• The longer microwaves are the ones that heat our food
in a microwave oven.
• Microwaves excite the water molecules in food. The
heated water cooks the food.
• If you had a sensitive microwave telescope in your
house, you would detect a faint signal leaking out of
your microwave oven!
• Microwave ovens are shielded to protect you from
overexposure.
• Microwaves are good for transmitting
information because they can penetrate haze,
light rain and snow, clouds, and smoke.
• Shorter microwaves are used for Doppler radar
used in weather forecasts.
• One microwave can carry 1000 telephone calls.
What is Radar?
• Radar stands for
"radio detection and
ranging.”
• Radar was developed
to detect objects and
determine their range
(or position) by
transmitting short
bursts of
microwaves.
Terahertz
• astronomers image gas and dust between stars
with them because they exist at low temperatures
in space
• very little enters our atmosphere so use
telescopes at high altitudes or in space to monitor
this type of radiation
• might be useful for high altitude communications
• future use to transfer data 1000 faster than with
microwaves!
Terahertz
• can see through clothing, paper,
wood, plastic and other nonmetallic
materials without harmful exposure
• Full Body Scan technology used by
Homeland Security for airport
screening at security check points
and to inspect packages
• can see through paint so might be
used to uncover and preserve
historic art work and murals
• might detect cancer and cavities in
teeth
Terahertz Rays are generated
when tape is removed.
INFRARED
• Discovered in 1709 when Herschel laid a
thermometer next to a rainbow. The
thermometer got hot! We experience
infrared as heat energy.
• "Near infrared" waves are shorter while
"far infrared" are longer (closer to
microwave portion of the spectrum).
Far Infrared
• We experience far
infrared as heat!
• These waves are
used to warm fast
food, grill in new
backyard barbecues,
and in heat seeking
missiles.
• Some snakes see
infrared. We need
night vision goggles!
• This is a picture of a
cat in infrared. The
orange areas are the
warmest and the
white-blue areas are
the coldest.
• This picture shows a
man holding up a
lighted match!
• The Earth, the Sun,
and far away things
like stars and galaxies
also give off infrared.
Near Infrared
Near infrared waves
are not hot at all - in
fact you cannot even
feel them. They are
used by your TV's
remote control.
New guitars use IR
pickups to eliminate
electric hum.
Oximeters measure the amount of oxygen in blood.
The oximeter compares how much
red light and infra red light is
absorbed by the blood.
Oxygenated blood absorbs light at
660nm (red light), whereas
deoxygenated blood absorbs light at
940nm (infra-red). The relative
absorption of each type of is used to
calculate the oxygen saturation level
of the blood.
Near Infrared radiation is also used to image
the internal structures of the sinuses during
surgery. This reduces exposure to radiation
during CT scans and reduces the risk of
injury to the brain and eyes during surgery.
Spitzer Space
Telescope
• Uses infrared to look at
star formation, centers of
galaxies, newly forming
planetary systems, and
cooler objects in space.
• The telescope must be
cooled to near absolute
zero (-459 degrees
Fahrenheit or -273
degrees Celsius) to work.
• Spitzer is the 4th and last in
NASA’s Great
Observatories Program.
Visible Light
Roy G. Biv
Ultraviolet
We learn
about stars
and galaxies
by studying
the ultraviolet
radiation they
give off.
Hubble Space Telescope
Hubble observes stars and galaxies in near ultraviolet. It
is one of NASA’s Great Observatories.
Photo of the Sun in Extreme Ultraviolet
Sunburn
While most
ultraviolet waves
from the Sun are
blocked by Earth's
atmosphere, some
get through.
Scientists
developed a UV
index to help
people protect
themselves.
UV Index
Category
Sunburn Time
over 9
extreme
less than 15
minutes
7-9
high
about 20 minutes
4-7
medium
about 30 minutes
0-4
low
more than 1 hour
Uses for Ultraviolet
•
•
•
•
•
•
•
Kill germs in goggle cabinet
Detect scratches on cornea of eye
Identify counterfeit money
Make cloth bright
Glow in the dark posters
Identify minerals
By some insects to see
What we see.
What a bee sees.
X RAYS
X rays go through our skin but cast shadows of
our bones onto film. Because their wavelengths
are so small, we talk about x-rays as photons. X
rays are dangerous!
The Foot-O-Scope was invented in the
1920s and used up until the 1960s for shoe
fitting. It gave off too much X-ray!
Engineering Disasters
https://www.youtube.com/watch?v=
wbMN6jueU1A
https://www.youtube.com/watch?
v=QVlEXd9w7vk
In space, black holes, neutron stars, binary
star systems, supernova remnants, stars, the
Sun, and even some comets emit X-rays. This
is a picture of our Sun in x-ray.
Chandra X-Ray Observatory
One of NASA’s Great Observatories, Chandra
has been in space since 1999.
NuStar launched June 13, 2012
uses X-rays to study black holes, active galaxies,
and supernova remnants
11th mission in NASA’s Small Explorer program
Image of the
black hole in the
center of our
Milky Way
Galaxy.
Gamma Rays
• produced by supernova explosions, the
destruction of atoms, and the decay of
radioactive material
• supernova explosions, neutron stars, pulsars,
and black holes are all sources of gamma-rays
• can kill living cells (gamma rays cause cancer
and can also be used to kill cancer)
• travel to us across the universe and are
absorbed – blocked! - by the Earth's
atmosphere
Compton Gamma Ray Observatory
CGRO satellite
being deployed
from the Space
Shuttle orbiter in
1991. NASA’s
Great Observatory
satellite worked
until 2000 when it
was deorbited.
Gamma Rays
• Uses for Gamma Rays
– find cracks in airplane wings and in nuclear
power plant piping
– fight cancer
• Danger from Gamma Rays on Earth
– meltdown of nuclear reactor in Ukraine
– meltdown of nuclear reactor in Japan
– radon gas build up in NJ homes
NJ’s Oldest Rocks
During radioactive decay,
uranium decays to lead.
The Sensitive High
Resolution Ion Microprobe
(SHRIMP) is a device that
determines the age of rock
by measuring its lead and
uranium content. This is
known as geochronology.
SHRIMP has dated some
of the oldest rocks and
crystals ever found - 4
billion years old!
2009
Gamma Knife in use at
Robert Wood Johnson
Hospital in New
Brunswick to treat brain
and spinal tumors. The
Gamma Knife uses
radiation in an approach
known as radiosurgery.
Each radiation beam is
too weak to damage
normal tissue but when
focused precisely on
the target, the radiation
is sufficient to treat the
affected area. The
radiation source used is
called cobalt 60.
Hospital Equipment
Many machines and treatments
contain radioactive substances. These
must be disposed of properly to keep
radiation levels from building up above
safe levels.
NJ’s Greensand Marl
Geiger Counter
DANGER From Space!
• Gamma-ray bursts can release more energy in
10 seconds than the Sun will emit in its entire 10
billion-year lifetime!
• So far, all bursts observed have come from
outside our Milky Way Galaxy.
• Eventually, a gamma-ray burst will occur in the
Milky Way. Life on Earth will end if the planet is
hit by a gamma ray burst.
Swift was launched in 2005. On April 13, 2010 its
“burst-o-meter” recorded its 500th gamma ray burst.
The Milky Way Galaxy as Seen in
Different Wavelengths
Multiwavelength Milky Way Images