Visible Light (PowerPoint) by ewghwehws

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									Visible Light
Region        Wavelength            Frequency
              (centimeters)         (Hz)
Radio         > 10                  < 3 x 109
Microwave     10 - 0.01             3 x 109 - 3 x 1012
Infrared      0.01 - 7 x 10-5       3 x 1012 - 4.3 x 1014
Visible       7 x 10-5 - 4 x 10-5   4.3 x 1014 - 7.5 x 1014
Ultraviolet   4 x 10-5 - 10-7       7.5 x 1014 - 3 x 1017
X-Rays        10-7 - 10-9           3 x 1017 - 3 x 1019
Gamma Rays    < 10-9                > 3 x 1019
• Visible light is the name we give the
  frequencies of electromagnetic waves our
  eyes can detect.
• Our retinas are made
  of cells called rods
  and cones
  – Cones allow us to see
    color, but they require
    more intensity (more
    waves) in order to
    send a message to the
    brain. For that reason,
    we can’t really see
    color when there isn't
    a lot of light.
– Rods allow us to
  detect movement and
  they don’t require as
  much intensity
  (waves) before they
  send a signal to the
  brain
• Everything that we see is due to the
  reflection of light.
• When you look at something your eyes are
  interpreting the light that is reflected off of
  it.
                                     Light from sun




                      Yellow light
                      reflected
• Opaque:
  – A word used to describe objects that don’t let
    light move through them (so you can’t see
    through them). This is either because they
    absorb or reflect light.
• Transparent:
  – A word used to describe objects that allow
    light to travel through them (so it’s almost like
    they aren't there at all).
• Fortunately for us the atmosphere is
  opaque to high frequency ultraviolet
  waves, but is transparent to visible light
  and some UV.
• When you see your shadow it is because
  you are blocking the light from getting
  through.
                    Color
• There are three different types of cones in
  our eyes. Because of this we are able to
  see the full range of the visible light
  spectrum.

• The color that you see when you look at
  something is actually the wavelengths of
  light that are being reflected.

• The colors you don’t see are being
  absorbed and converted into heat energy.
• ROYGBIV

• Red is the lowest frequency light

• Violet is the highest frequency

• All of the colors we see are combination of
  wavelengths of visible light.
• When every wavelength of visible light hits
  your eyes, they perceive it as white
  – Because of this we call it “white light”
  – This is what you see when you look at light
    from the sun and most light sources, such as
    lamps.

• Something that reflects every wavelength
  looks white to you.

• What do you think something that absorbs
  all frequencies of light looks like?
What frequencies of light are being
reflected from / absorbed by this dog?

   = green is being
   reflected, every
   other color is being
   absorbed

   = every other color
   is being reflected/
   green is being
   absorbed
What frequencies of light are being
reflected from / absorbed by the orange?

   = every other color
   is being reflected/
   orange is being
   absorbed

   = orange is being
   reflected, every
   other color is being
   absorbed
What frequencies of light are being
reflected / absorbed from the black parts
of the 8-ball?
     = black light is
     being reflected.

    = every color is
    being reflected

    = every color is
    being absorbed
What frequencies of light are being
reflected / absorbed from the seal?

    = every color is
    being absorbed.

    = every color is
    being reflected
• Something that absorbs every frequency
  of light looks black to you.

• An object that is transparent but colored,
  like stained glass, looks that way because
  it only allows light of certain frequencies
  through, the rest it absorbs.

• For example red stained
  glass only lets red through
  and absorbs everything
  else.
What would you see if you shined pure
green light on a red rose?

    = the rose would look red

    = the rose would look green

    = the rose would look black

    = the rose would look white
                    Pigments
• Pigments are particles that absorb and
  reflect specific frequencies of light.

• We can use these to dye things:
  – If you dye a shirt with blue pigment you are
    dying it with particles that absorb everything
    but blue light.

  – If you mix all pigments together, that means
    all light will be absorbed and so that object will
    look black.
• When light hits a surface, it can be bent
  (refracted), bounced (reflected) or
  absorbed.

• Whether light is reflected, refracted or
  absorbed depends on how it interacts with
  the atoms of the material.
             Reflection of Light

• When light is returned into the medium it
  came from we say it is reflected

• How light is reflected depends on the
  roughness of the surface:

  – Smooth surfaces: non-diffuse reflection
  – Rougher surfaces: diffuse reflection
• Light will always reflect from a surface at
  an angle equal to the angle it hit the
  surface at.
• Incoming light is called the incident ray
• The angle the light strikes the surface at is
  called the angle of incidence

                         a = angle of incidence
                    a
     incident ray
• Reflected light is called the reflected ray
• The angle that light is reflected from a
  surface is called the angle of reflection
• The angle of incidence will always be
  equal to the angle of reflection.
                                        b = angle of reflection



                    b



                        reflected ray
                   Mirrors
• When you see yourself in the mirror it is
  because light is reflected off of you from a
  light source, hits and is reflected off of the
  mirror and is interpreted by your eyes to
  give a virtual image.



                                        Virtual image
• Convex mirrors:
virtual image
is smaller




• Concave mirrors:
virtual image
is larger
• With concave and convex
  mirrors the angles of
  incidence and reflection
  are still equal, but the
  surfaces are bent so it
  changes how your eye
  interprets the reflected
  light.
• Sometimes objects don’t reflect light in an
  ‘organized’ way.
• Scattering is when light is reflected in all
  different directions.
• Example:
  – Nitrogen and oxygen scatter the higher
    frequencies of light (blue and violet) really well.
    This is why the sky is blue.
  – Clouds scatter all light
    equally which is why they
    appear white.
• What is the word used to describe when a
  wave is bent?
    refraction

• Refraction occurs when a light wave is
  bent as it moves from one medium to
  another.

• This happens because light travels at
  different speeds in different mediums.
Which ray is the refracted ray?




 = Ray A

 = Ray B

 = Ray C

 = Angle x3
Which ray is the reflected ray?




 = Ray A

 = Ray B

 = Ray C

 = Angle x3
Which ray is the incident ray?




 = Ray A

 = Ray B

 = Ray C

 = Angle x3
Which angle is the angle of incidence?




 = Angle x1

 = Angle x2

 = Angle x3
Which angle is the angle of reflection?




 = Angle x1

 = Angle x2

 = Angle x3
Which angle is the angle of refraction?




 = Angle x1

 = Angle x2

 = Angle x3
• The speed of light is slower in glass,
  water, air and denser, cooler air.
What does it mean when someone is color
                 blind?

								
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