Light

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Light

• Jayne Robinson

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19 1 Electromagnetic Radiation

• Electromagnetic spectrum energy waves that
  include radio waves, infrared, visible light,
  ultraviolet, x-rays, and gamma rays. They are
  transverse rays. See chart 19-2 p. 485
• Electromagnetic waves carry energy by radiation
  they can travel through a medium and through a
  vacuum (space).
• All electromagnetic waves travel at 300 000
  km/sec or 300 000 000 m/sec (3.00 x 108 m/s) This
  is the speed of light (c) it is also the speed of
  any of these waves in a vacuum or medium.
• Light is composed of tiny particles of radiation
  called photons they have no mass.

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19 1 Electromagnetic Radiation

• Radio waves long wavelengths, low frequency,
  lowest photon energy.
• Radio waves are used to transmit sound waves
  these machines change sound waves to electrical
  currents through modulation. The machines then
  change the electrical currents back to sound
  waves.
• Radio waves include microwaves (used in
  communications), AM FM radio, radar, shortwave
  radio, television.

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19 1 Electromagnetic Radiation

• Infrared waves longer wavelengths than visible
  light, infrared is warm warm objects give off
  more infrared radiation than cool objects. Night
  vision goggles use the infrared radiation of
  animals to see animals. Medical diagnosis use
  infrared to detect tumors infrared lamps are
  used to keep food warm and to dry paint. (p. 487)
• Visible light only a small portion of the
  electro-magnetic spectrum is visible. Light can
  stimulate chemical reactions (photosynthesis).
  (see chart pg 485)

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19 1 Electromagnetic Radiation

• UV radiation higher frequency , shorter
  wavelengths, than visible light. Energy is
  greater than visible light. Because this energy
  is greater, overexposure can cause cancer. The
  ozone layer is a natural filter. However, we do
  need some UV in order to produce vitamin D for
  bones and teeth. UV radiation is also used to
  kill bacteria and microbes in foods and on
  utensils.

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19 1 Electromagnetic Radiation

• X rays x-rays have shorter wavelengths,
  higher frequencies than UV. They can travel
  through less dense skin muscle but not through
  bone so they form an image.
• Gamma rays g have the highest frequency and
  the lowest / shorter wavelength radioactive
  used to treat cancer.

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19 2 Light Color

• Light rays pass through objects at different
  values. A color appears b/c of the light rays
  the object reflects (a green shirt reflects green
  rays, absorbs all other).
• The type of matter in an object determines the
  amount of light absorbed or reflected.
• Opaque absorb or reflect all light so you cant
  see through the substance.
• Transparent light rays pass through so you can
  see through (most glass)
• Translucent some light passes through but you
  cant see clearly (wax paper, frosted glass,
  white paper)

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19 2 Light Color

• Objects appear a particular color b/c of the
  reflected rays. Black absorbs all light (so it
  gets hot) white reflects all rays (so it is
  cooler).
• Rods and cones are the nerve cells in the eye
  that allow us to see colors rods allow us to
  see in dim light, cones allow us to see colors.
• Red cones absorb mostly red yellow
• Green cones absorb mostly green yellow
• Blue cones absorb mostly blue violet

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19 2 Light Color

• To see yellow, the red green cones respond
  combine to interpret yellow
• To see bright blue, the green blue cones
  combine to interpret bright blue (see p. 494)
• You see white light when all cones respond (white
  light is a mixture of all light rays)
• The wavelength of visible light gets shorter
  across the spectrum Red (longest l), Orange,
  Yellow, Green, Blue, Indigo, Violet (shortest l).
  ROYGBIV (rainbow)

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19 2 Light Color

• Filters can be used on bright lights (spotlights)
  to change colors. It will transmit only that
  color. A pink filter will make everything look
  pink (or black/grey if it is not pink or red) b/c
  it reflects that one color wavelength and absorbs
  all other wavelengths.

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19 2 Light Color

• Pigments materials and chemicals that absorb
  some colors reflect others. Pigments are
  opposite of cones yellow pigments reflect red
  green light waves and absorb blue. (p. 495)
• Light rays are additive b/c they combine
  produce white light.
• Pigments are subtractive b/c they combine to
  produce black and black is the absence of color.

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19 3 Battle of the Bulbs

• Incandescent Light produced by electricity
  passing through/across a tungsten filament,
  causing the filament to heat up and glow. The
  bulb is hot to the touch.
• Fluorescent lights are filled with a gas and
  coated on the inside of the glass tube with
  phosphers (fluorescent materials that give off
  light when they absorb UV radiation).
  Electricity passes through the tube, collide with
  the gas molecules causing them to give off UV
  radiation which is absorbed by the phosphors,
  causing them to glow.

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19 3 Battle of the Bulbs

• Fluorescent lights are much less expensive to use
  than incandescent. For each bulb replaced in the
  home, about 20 per bulb can be saved yearly on
  electric bills. Also, the use of fossil fuels
  would decrease creating less pollution.

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19 4 Wave properties of Light

• Reflection occurs when light waves/rays strike an
  object and bounce off. Light and
  electromagnetic waves, sound and water waves can
  all be reflected.

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19 4 Reflection

• Incident beam or wave is the wave that strikes an
  object.
• Reflected beam or wave is the wave that bounces
  off.
• Normal is the perpendicular line drawn to the
  surface the waves hit.
• Angle of incidence (i) the angle between the
  incident beam and the normal.
• Angle of reflection (r) angle between the
  reflected beam and the normal.

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19 4 Reflection

• Law of reflection angle of incidence (i) equals
  angle of reflection (r)
• smooth surface
• Smooth surfaces reflect light waves in one
  direction rough surfaces scatter waves.

i
r
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19 4 Wave properties of Light

• Refraction the bending of light waves caused by
  a change in speed. The light waves change speed
  when they pass through a substance with a
  different density.

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19 4 Refraction

• Normal the line perpendicular to the surface
  the light is moving into
• Angle of incidence (i) angle between the normal
  and the surface the wave is entering.
• Angle of refraction (r) angle between normal
  and inside the entered medium.
• See diagram 19-17 page 502

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19 4 Refraction

• When light passes into a more dense substance, it
  travels slower so it bends toward the normal.
• When light passes into a less dense substance, it
  travels faster and bends away from the normal.
• When light passes through a prism it bends
  according to wavelength. Violet (shortest
  wavelength) light bends the most, red (longest
  wavelength) bends the least, and a rainbow is
  formed. ROYGBIV

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