Physical Science

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Physical Science

• Ch. 12 13 Electromagnetic Waves and Light

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Electromagnetic Radiation

• Electromagnetic waves (E.M.) are transverse waves
  produced by the motion of electrically charged
  particles (photons).
• E.M. waves do not require a medium, and are
  therefore able to travel at 186,000 mi/s (300,000
  km/s), the speed of light (which is an E.M. wave).

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Does Light Have Mass?
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• Well.maybe.

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Electromagnetic Spectrum

• The different electromagnetic waves are arranged
  in the electromagnetic spectrum in order of
  increasing frequency and decreasing wavelength.
• The higher the frequency, the more photons
  (energy) per wave, and the more potentially
  harmful the wave is.

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• Low energy High energy

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Radio Waves

• Radio waves are the lowest frequency E.M. wave.
• They are used primarily for communications, such
  as cell phones, t.v. and radio transmissions, and
  cordless devices such as phones, speakers, etc.

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Microwaves

• Microwaves are a type of radio wave. They are
  used in cell phones and microwave ovens.
• At normal levels, microwaves are harmless.

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• Why shouldnt you put metal objects (or CDs) in
  a microwave?
• Metal foil
• CD
• Bulb
• Chips

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Infrared Radiation

• Infrared radiation transfers energy in the form
  of heat.
• Examples include heat lamps and the warmth from
  the sun. Special types of film and cameras can
  show infrared radiation. This is called
  thermography.

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Visible Light

• Visible light can be separated into 7 different
  colors. From lowest frequency to highest, they
  follow the acronym ROY G. BIV
• When all 7 colors are combined together they
  produce white light.

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• When all 7 colors of the spectrum are absent,
  then the color black is produced.
• What is a black light and how does it work?

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Colors

• When an object appears a certain color, it is
  because that is the color which is being
  reflected back to your eye, just like a mirror.
• A white object reflects all colors, a black
  object reflects no color.

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Visible Light Spectrum

• A prism can separate visible light into the 7
  different colors.
• Drops of moisture in the atmosphere can act as a
  prism, and form a rainbow.

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• A pigment is a colored material which is used to
  change the color of other materials.
• The 3 primary pigments are magenta, cyan, and
  yellow (pg. 393). These colors can be combined
  to produce any other color of pigment.

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• So if you go to the store and pick out a certain
  color of paint, odds are they will not have that
  color on the shelf. But they will mix the
  correct proportions of the primary pigments
  together to create your color.

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• Visible light can also cause certain chemical
  reactions to occur.
• Examples photosynthesis, milk spoiling, H2O2
  breakdown

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• Is it possible to see in the dark?

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Ultraviolet Light (U.V.)

• U.V. rays are potentially dangerous at high
  levels or with prolonged exposure.
• U.V. rays can cause sunburns and skin cancer, and
  kill bacteria and healthy cells.

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• The ozone layer of the atmosphere blocks most
  u.v. rays from reaching the earth.
• Using sunscreens with high S.P.F. ratings can
  also help protect your skin from u.v. rays.

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X-Rays

• X-rays are high frequency e.m. waves which are
  potentially dangerous at moderate levels.
• X-rays can penetrate many materials such as skin,
  muscle, and many fabrics.

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• X-rays are used in dental and medical procedures,
  and can cause cancer and decrease a persons life
  expectancy with prolonged exposure.

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Gamma Radiation

• Gamma radiation is high frequency waves which can
  be extremely dangerous.
• Potentially dangerous gamma rays may be given off
  from radioactive materials, and are present
  everywhere on earth at low safe levels.

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• Gamma radiation can kill healthy cells, but can
  also be used to kill cancerous cells. This is
  called radiation therapy.

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Classifications of Materials

• Different materials can be classified by how they
  allow waves (usually light) to pass through them.
• These classifications are opaque, translucent,
  and transparent.

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• Transparent materials allow almost all visible
  light to pass through.
• Ex. glass, plastic wrap

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• Translucent materials allow a partial amount of
  visible light to pass through.
• Ex. wax paper, shower doors, plastic milk
  jugs

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• Opaque materials stop almost all visible light
  from passing through.
• Ex. drywall, thick curtains

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Types of Lighting

• There are 2 main types of artificial lighting.
• 1. Incandescent a heated filament excites the
  gases inside an enclosed bulb.

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• 2. Fluorescent an electric current is
  transferred through a glass tube filled with a
  conductive gas. A small amount of mercury inside
  emits u.v. rays when energized. These rays
  excite phosphors on the inside of the tube,
  producing light.

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Polarized Light

• Normal light will produce waves which vibrate in
  many different planes.
• Polarized light is light which vibrates in only 1
  plane. This is created by passing normal light
  through a polarized lens.

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• Polarized lenses block all light waves except
  those moving in 1 particular plane.

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• Think of polarized lenses like tines on a comb.
  Normal light that passes through the lens, like
  tangled hair through a comb, will align in the
  same plane.

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• Polarized glass and lenses are effective at
  blocking out glare from the sun.
• As a result they are used in car windshields,
  sunglasses, and camera lenses.

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Lasers Coherent Light

• Coherent light is visible light traveling at only
  1 specific wavelength (resulting in 1 color).
  This wave has all of its crests and troughs
  aligned and travels in only 1 direction. A laser
  is an example of coherent light.

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• A laser is a device used to create a beam of
  coherent light.

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Lasers

• In a laser, an electric current excites a
  material (like neon) and causes it to emit
  photons. These photons are enclosed inside the
  laser device where they bounce back and forth
  between 2 mirrors and becomes perfectly aligned
  (coherent light).

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• Some of these photons, if they are aligned
  correctly, escape through a small portion of one
  of the mirrors. This is the laser beam.

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• Think of it like a piggy bank. If you want to
  get some money out through the top slit, the
  coins have to line up perfectly before they will
  come out.

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• Since laser beams are perfectly aligned and move
  in the same exact direction, they spread out very
  little.

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Total Internal Reflections

• Normally, when a wave enters a medium it is
  either reflected or re-emitted out of the medium.
• However, when a wave entering a medium is
  completely reflected back into the material
  instead of out of it, this is called a total
  internal reflection.

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• Optical fibers (Fiber optics) produce a total
  internal reflection. Such fibers can be used for
  communications, entertainment, and surgeries.
• Certain fluorescent plastics produce
  internal reflections which may make them appear
  to glow.

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• A mirage is a visual distortion produced by the
  refraction of light.
• Some mirages produce a mirror or a watery image,
  and others may make an object appear larger or
  smaller, nearer or further away.

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• This device produces a false image, but not a
  true mirage.

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• Paul bought a very bright LED flashlight. He
  showed Dave how bright it was by shining a
  regular light in his eyes, and then the LED.
  After viewing the LED for a few seconds, the room
  suddenly appeared darker to Dave. Why?

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• Not to be outdone, Dave then pulls out a laser
  pointer which he had and said, Well just look at
  how bright this one is.
• Bad idea. Why?

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• I cdnuolt blveiee taht I cluod aulaclty
  uesdnatnrd waht I was rdanieg. The phaonmneal
  pweor of the hmuan mnid. Aoccdrnig to rscheearch
  at Cmabrigde Uinervtisy, it deosn't mttaer in
  waht oredr the ltteers in a wrod are, the olny
  iprmoatnt tihng is taht the frist and lsat ltteer
  be in the rghit pclae. The rset can be a taotl
  mses and you can sitll raed it wouthit a porbelm.
  Tihs is bcuseae the huamn mnid deos not raed
  ervey lteter by istlef, but the wrod as a wlohe.
  Amzanig huh?

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• How do you suppose they were able to etch the
  image into the middle of the glass cube?

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• Todd was showing a friend how his black light
  worked, when his white cat walked in the room.
  What color did the cat appear under the black
  light, and why?

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• Les spilled a little bit of oil into the water as
  he was working on his boat. This caused a
  rainbow effect to appear. Why do you think this
  occurred?

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• Karen went to the beach last week, and because it
  was a cloudy day she did not use any sunscreen.
  To her dismay, she came back with a slight
  sunburn. How is this possible?

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• How is one universal remote able to control all
  of the components in your entertainment system
  (tv, DVD, cable box, etc.) by itself)

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• In art class, Andy was mixing watercolors
  together to obtain the right shades for his
  project. He found that using the 3 primary
  pigment colors, there were only 2 main colors
  which he could not produce. What were they?

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• When asked what he was doing outside on the
  ground, Beaman replied, Creating constructive
  interference by simultaneous refraction of
  mid-level electromagnetic radiation through a
  convex lens, in order to harness their combined
  energies and thermally terminate formicidae
  hymenoptera with extreme prejudice.
• What was he doing?

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