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Chapter 19
               EM Spectrum
•   Electromagnetic
    Spectrum (EM) -
    includes radio
    waves, microwaves,
    infrared waves,
    ultraviolet rays, x-
    rays, gamma rays,
    and visible light.
       Electromagnetic Waves
• Are transverse waves
  that are produced by
  the motion of
  electrically charged
  particles. These
  waves are often
  radiation because
  they radiate from
              EM Waves
• Do not need a medium to transfer energy.
• They can travel through a vacuum at a
  speed of 300 000 km/s.
     Describing EM Radiation
• All EM waves travel at the same speed in
  a vacuum, but their frequency and
  wavelengths can vary.
              EM Spectrum
• Low Frequency, Long-wave length radio
  waves to high frequency, short wavelength
  gamma rays.

• Page 529.
              EM Waves
• Radio Waves
• Infrared Radiation
• Visible Radiation- only part of spectrum
  we can see.
• Ultraviolet Radiation –
• X-Rays and Gamma Rays
                    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
• C. When light strikes
  matter three things can
  happen – it can be
• reflected, or
• Light that is absorbed
  is taken in by the
       matter it strikes.
• Black objects absorb
  all light-best color
       for absorption.
• Light that is reflected
  bounces off the
  substance it strikes.
•    Example: Mirrors
          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
• Examples: wood and metal.
•   Reflected light is
    bounced light.
•   How to predict how
    reflected light will
    –   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
•   Light travels in a straight line.
•   Light can bend and change
    direction ie. Reflection,
•   Refraction is when light
    passes at an angle from one
    medium into another medium
    so it changes direction or
•   Example: you may have
    experienced refraction when
    reaching into a fish tank to
    pick up an item.
•   Light travels at different speeds through
    different mediums.
•   The speed light travels depends upon
    the density of the medium.
– Light that moves straight on from one
  medium to another does not bend. It is not
        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.
    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
       What color do you see?
• Concave Concave Mirror Focuses Colors
          Mirror Focuses Colors
            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.
        Transparent Objects
• Transparent Objects – The color of a
  transparent object is the color that passes
  through the object. (all other colors
• Transparent objects transmit only some
  colors and others are absorbed or blocked
  – these substances are called filters.
                 What is a lens?

• Lens is a transparent
  substance that bends or
  refracts light in a definite
• Can be glass or plastic.
• Found in every optical
  device ie. Binoculars,
• Have one or two curved
            Two main types
              of 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.
             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.
            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.
       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.
      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
     Convex Lens is Inverse
     of Concave Lens

• Convex Lens is Inverse
             Convex Lens is Inverse
              of Concave Lens
   of Concave Lens
• Image Formation with Lenses If object is
  far from the
  lens (beyond)
  the focal
  point, a real
  inverted image
  is formed

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