The Electromagnetic Spectrum

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Chapter 4

• The Electromagnetic Spectrum
• Part 2

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Radio waves

• Includes FM, AM, radar and TV waves
• Used in many devices such as remote control
  items, cell phones, wireless devices, etc.

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Microwaves

• First used in radar, now used in communication
  (wireless LAN networks), and consumer use
  (microwave ovens).
• medical applications in cancer treatment (destroy
  tumors by heating them).
• Most radio astronomy uses microwaves
• Active Denial System the Pain Ray

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• Microwaves
• The Active Denial System (ADS) is a non-lethal
  weapon developed by the U.S. military. It is a
  micro-wave transmitter used for crowd control.
  Informally, the weapon is also called the pain
  ray. The ADS works by directing microwave
  radiation toward the subjects. The waves excite
  water molecules in the epidermis to around 130 F
  (55 C), causing an intensely painful sensation
  of extreme heat. While not actually burning the
  skin, the burning sensation is similar to that of
  a light bulb being pressed against the skin.
• Wireless LAN (Local Access Network) protocols,
  such as Bluetooth also use microwaves.

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The Cloak of Invisibility

• Physicists in Texas have developed a method to
  make objects "invisible" within a limited range
  of light waves.
• It's not Harry Potter's invisibility cloak just
  yet, but scientists say it has a lot of potential.

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The Cloak of Invisibility

• Light and invisibility
• We see things because light reflects off of them
  and hits our eyes. Or, in this case, microwaves
  bounce off of them and hit a detection device.
• Light has properties that can be manipulated,
  which is how objects can be rendered invisible.
  It can be reflected away, for example.
• Illusionists can use mirrors to make an object
  disappear.

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• Light also refracts -- or breaks -- when it
  passes through a prism or raindrops, resulting in
  the colors we see in a rainbow.
• Light also bends ever so slightly due to gravity,
  when it passes by a planet.

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• Previous attempts at achieving invisibility have
  involved bending or reflecting light around the
  object that is meant to vanish.
• The mantle cloak takes a new approach.
• Light is a wave that can be disturbed. That's
  what the mantle cloak does.

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The cloak's material

• The cloak is made by combining copper tape with
  polycarbonate, a material commonly used in DVD's
  and CDs. The resulting cloak has a tiny pattern
  that neutralizes the waves bouncing off of it.

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• For it to work, the material's pattern has to be
  roughly the size of the wavelength of light to be
  canceled out. Unfortunately that only allows it
  to work on a limited range of wavelengths.

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• Current technology allows the cloak to work with
  only microwaves but scientists say the principle
  behind the cloak can also be used for visible
  light.

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• So far it has only been able to hide objects from
  the human eye that are so tiny that we can't see
  them anyway.
• However, scientists believe that this could "pave
  the way" for larger objects to be rendered
  invisible.

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• Infrared
• Missile guidance systems use the emission from a
  target of electromagnetic radiation in the
  infrared part of the spectrum to track it.
• Infrared radiation can be used as a heating
  source. For example it is used in infrared
  saunas, and also to remove ice from the wings of
  aircraft (de-icing).
• Infrared thermomedic therapy uses thermal
  technology to provide compressive support and
  healing warmth to assist symptom control for
  arthritis, injury pain.
• IR data transmission is also employed in
  short-range communication among computer
  peripherals and personal digital assistants
  (PDAs)
• Weather satellites produce infrared images to aid
  in the prediction of weather.

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Infrared Waves

• Infrared radiation is popularly known as "heat"
• Used in heat lamps, de-icing systems and
  thermomedic therapy.
• Missile guidance systems, short range
  communication systems
• Weather satellites

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Can be detected with special devices such as
night goggles
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Weather satellites track weather systems using
infrared.
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Visible Light

• The portion of the electromagnetic spectrum that
  human eyes can detect
• ROY G BIV (red, orange, yellow, green, blue,
  indigo, violet)
• Red is the lowest frequency and violet is the
  highest frequency

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Visible Spectrum We perceive electromagnetic
energy having wavelengths in the range 400-700
nm as visible light.
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• Ultraviolet Radiation
• To help thwart counterfeiters, sensitive
  documents (e.g. credit cards, driver's licenses,
  passports) may also include a UV watermark that
  can only be seen when viewed under a UV-emitting
  light.
• Some brands of pepper spray will leave an
  invisible chemical (UV Dye) that is not easily
  washed off on a pepper sprayed attacker, which
  would help police identify them later.
• Fluorescent lamps produce UV radiation by
  ionizing low-pressure mercury vapor. A
  phosphorescent coating on the inside of the tubes
  absorbs the UV and converts it to visible light.
• Some animals can see into the near ultraviolet.
• Many insects use the ultraviolet wavelength
  emissions from celestial objects as references
  for flight navigation.
• Ultraviolet traps called bug zappers are used to
  eliminate various small flying insects. They are
  attracted to the UV light, and are killed using
  an electric shock.

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Ultraviolet

• Can cause skin cancer and blindness in humans
• Used in tanning beds and sterilizing equipment
• UV watermarks
• UV identification

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Bee vision is very different from human vision,
they perceive colors we are simply incapable of
seeing. Most insects have light sensitive cells,
or photoreceptors, that are sensitive to
ultraviolet light.
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X-Rays

• Primarily used in medicine.

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X-Ray Scanners
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X-Ray Diffraction

• The diffraction of X-rays is used to disperse
  X-rays in a spectrometer and to determine the
  structure of crystals or molecules.

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• Gamma radiation
• Gamma radiation can impart significant damage to
  a living cell. This property means that gamma
  radiation is often used to kill living organisms,
  in a process called irradiation. Applications of
  this include sterilizing medical equipment and
  removing decay-causing bacteria from food.
• Due to their tissue penetrating property, gamma
  rays have a wide variety of medical uses such as
  in CT Scans and radiation therapy. However they
  have the ability to cause cancer as well.
• Despite their cancer-causing properties, gamma
  rays are also used to treat some types of cancer.
  The procedure called gamma-knife surgery uses
  multiple concentrated beams of gamma rays in
  order to kill cancerous cells.
• Gamma rays are also used for diagnostic purposes
  in nuclear medicine to track radioisotopes that
  are administered to a patient.
• In the US, gamma ray detectors are used as part
  of the Container Security Initiative (CSI). The
  objective of this technique is to pre-screen
  merchant ship containers before they enter US
  ports.

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Gamma rays

• Highest energy and most dangerous type of
  radiation.
• Can cause cancer through damage to DNA.
• Blocked from Earths surface by atmosphere.
• Used in medicine and irradiation.

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Irradiation
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Gamma Knife
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Electromagnetic Waves
A
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Demonstrations

• Light is a Wave Using Polarizers.
• Colored Slides.
• Ne and Ar spectral tubes.

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Star Finder Video Electromagnetic Spectrum (Stop
at 428)
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Homework

• Chapter 4 Worksheet 2