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The Electromagnetic Spectrum

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Chapter 4 The Electromagnetic Spectrum Part 2 Electromagnetic Waves A Demonstrations Light is a Wave Using Polarizers. Colored Slides. Ne and Ar spectral tubes. – PowerPoint PPT presentation

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Date added: 26 October 2019
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Title: The Electromagnetic Spectrum


1
Chapter 4
  • The Electromagnetic Spectrum
  • Part 2

2
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3
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4
Radio waves
  • Includes FM, AM, radar and TV waves
  • Used in many devices such as remote control
    items, cell phones, wireless devices, etc.

5
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

6
  • 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.

7
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8
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.

9
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.

10
  • 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.

11
  • 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.

12
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.

13
  • 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.

14
  • 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.

15
  • 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.

16
  • 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.

17
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

18
Can be detected with special devices such as
night goggles
19
Weather satellites track weather systems using
infrared.
20
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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22
Visible Spectrum We perceive electromagnetic
energy having wavelengths in the range 400-700
nm as visible light.
23
  • 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.

24
Ultraviolet
  • Can cause skin cancer and blindness in humans
  • Used in tanning beds and sterilizing equipment
  • UV watermarks
  • UV identification

25
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26
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.
27
X-Rays
  • Primarily used in medicine.

28
X-Ray Scanners
29
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.

30
  • 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.

31
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.

32
Irradiation
33
Gamma Knife
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35
Electromagnetic Waves
A
36
Demonstrations
  • Light is a Wave Using Polarizers.
  • Colored Slides.
  • Ne and Ar spectral tubes.

37
Star Finder Video Electromagnetic Spectrum (Stop
at 428)
38
Homework
  • Chapter 4 Worksheet 2
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