Light

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Light

• Chapter 19

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EM Spectrum

• Electromagnetic Spectrum (EM) - includes radio
  waves, microwaves, infrared waves, ultraviolet
  rays, x-rays, gamma rays, and visible light.

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Electromagnetic Waves

• Are transverse waves that are produced by the
  motion of electrically charged particles. These
  waves are often called electromagnetic radiation
  because they radiate from particles.

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EM Waves

• Do not need a medium to transfer energy.
• They can travel through a vacuum at a speed of
  300 000 km/s.

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Describing EM Radiation

• All EM waves travel at the same speed in a
  vacuum, but their frequency and wavelengths can
  vary.

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EM Spectrum

• Low Frequency, Long-wave length radio waves to
  high frequency, short wavelength gamma rays.
• Page 529.

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EM Waves

• Radio Waves
• Infrared Radiation
• Visible Radiation- only part of spectrum we can
  see.
• Ultraviolet Radiation
• X-Rays and Gamma Rays

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Light Facts

• A. Light travels in a straight line at a speed
  of 300,000 km per second.
• B. Light needs no medium in order to travel. It
  can move through a vacuum.
• C. When light strikes matter three things can
  happen it can be absorbed,
• reflected, or transmitted.

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Absorbed

• Light that is absorbed is taken in by the matter
  it strikes.
• Black objects absorb all light-best color for
  absorption.

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Reflected

• Light that is reflected bounces off the substance
  it strikes.
• Example Mirrors

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Transmitted Light

• Light that is transmitted passes through the
  matter it strikes.
• Examples Window glass, water, and air.
• Translucent objects that you can see light
  through but not
• any details examples are waxed paper and frosted
  glass.
• Opaque substances cannot be seen through at all
• Examples wood and metal.

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Reflection

• Reflected light is bounced light.
• How to predict how reflected light will behave.
• A single beam of light is called a ray.
• Incident ray is the ray that hits a mirror.
• Reflected ray is the ray that bounces off the
  mirror.

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Refraction

• Light travels in a straight line.
• Light can bend and change direction ie.
  Reflection, refraction
• Refraction is when light passes at an angle from
  one medium into another medium so it changes
  direction or bends.
• Example you may have experienced refraction
  when reaching into a fish tank to pick up an item.

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• Light travels at different speeds through
  different mediums.
• The speed light travels depends upon the density
  of the medium.

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• Light that moves straight on from one medium to
  another does not bend. It is not refracted.

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What is the spectrum?

• Prism is an object that breaks up light into the
  visible spectrum.
• Colors of the visible spectrum ROY G BIV (order
  never changes) red, orange, yellow, green, blue,
  indigo, violet
• Variety of colors depends upon the frequency of
  light energy.
• Every color has a different frequency.
• Red has the lowest frequency. And violet has the
  highest frequency.

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What gives an object its color?

• The color we see depends upon whether the object
  is opaque or transparent. The color also depends
  upon how much of the light is reflected,
  absorbed, or transmitted.

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What color do you see?

• Concave Mirror Focuses Colors         

Concave Mirror Focuses Colors         
                                                             
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Opaque Objects

• Opaque Objects The color of the object is the
  color reflected. Red objects reflect red light.
  
• White objects reflect all the colors that make
  up white light.
• Black objects absorb all colors that strike it.

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Transparent Objects

• Transparent Objects The color of a transparent
  object is the color that passes through the
  object. (all other colors absorbed).
• Transparent objects transmit only some colors and
  others are absorbed or blocked these substances
  are called filters.

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What is a lens?

• Lens is a transparent substance that bends or
  refracts light in a definite way.
• Can be glass or plastic.
• Found in every optical device ie. Binoculars,
  telescopes
• Have one or two curved surfaces.

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Two main typesof lenses

• convex lens is thicker at the center than at the
  edge. Magnifies to make things look bigger.
• A convex lens focuses light rays. The point
  where the light rays meet or converge is called
  the focal point.
• Used in projectors and cameras.

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Concave lens

• This lens is thinner at the center than at the
  edge.
• Makes things look smaller
• Spreads out light rays.
• Often used with convex lenses to give a sharper
  image.

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How do we see?

• Eye has several transparent parts.
• Each part refracts light that enters the eye.
• In a normal eye, light rays converge exactly upon
  the retina.
• The retina is the back part of the eye, made of
  two kinds of nerves.
• Rods - sensitive to brightness but not color.
• Cones sensitive to color.

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How do eyeglasses help?

• Normal eyes see clearly. The light rays enter
  the eye and converge upon the retina. Some eyes
  however, the length of the eyeball is not right.
  It is either too long or too short which causes
  the image to be out of focus.

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Two types of blurred vision

• near sightedness slightly longer eye. Light
  rays meet in front of retina. Corrected by
  concave lenses.
• Farsightedness slightly shorter eye. Light
  rays meet beyond the retina. Corrected with
  convex lens.
• Draw Concave lens Draw Convex Lens

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Convex Lens is Inverse     of Concave Lens     
          
Convex Lens is Inverse     of Concave Lens     
          

• Convex Lens is Inverse     of Concave Lens     
            

                                             
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• Image Formation with Lenses If object isfar
  from thelens (beyond)the focal point, a
  realinverted imageis formed

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