PHY 101 – Introduction to Physics_1_

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					       PHY 112 – General Physics II
n   MWF 8-9:50 am or 11-12:50 pm
n   Instructor: Heidi Van Tassell
n   Office: PS 211
n   Office Hours:
         Monday: 10:00-10:50 am in PS106
         Tuesday: 12:30-1:30 pm in PS106
         Wednesday: 10:00-10:50 am in PS106
         Thursday: 12:00-1:00 pm in PS100 (Tutoring Center)
         Friday: 10:00-10:50 am in PS106
n   Email: vantassell@mesacc.edu
n   Webpage: www.mesacc.edu/~vantassell

                        ASU PHY112 - Van Tassell - 1/28/2011   1
         Announcements
n Exam   4
 ¨Friday2 December 2011
 ¨Chapters 23, 24




             ASU PHY112 - Van Tassell - 1/28/2011   2
                      Refraction
n   When light reaches a boundary between two media it
    may either reflect off the boundary and return through
    the media it came, or it will pass through the new
    media.

n   Refraction is the bending of light rays as they pass
    from one media to another.



                      ASU PHY112 - Van Tassell -4/16/2007    3
                      Refraction
n   Refraction occurs due to the difference in the speed of
    light in different media.

n   Atoms in the materials absorb, reemit, and scatter the
    light causing delays in the transmission of the light.

n   This slowing of light causes wave fronts to bend at the
    boundary as part of the wave front move at different
    speeds.


                      ASU PHY112 - Van Tassell -4/16/2007     4
                      Refraction
n   The index of refraction measures the extent to which
    light is slowed in a medium as compared to vacuum.




n   A table of refractive indices is available on page 808 of
    your text.


                       ASU PHY112 - Van Tassell -4/16/2007      5
                       Refraction
n   Snell’s law describes how much light is bent at a
    boundary:



n   As with the law of reflection, angles for refraction are
    measured relative to the normal to the boundary.




                        ASU PHY112 - Van Tassell -4/16/2007    6
                         Refraction
n   Example: The drawing shows three layers of liquids, and a ray of
    light incident on the top layer. What angle does the ray of light
    make with the normal in the different materials?




                          ASU PHY112 - Van Tassell -4/16/2007       7
                       Refraction


n   Example: The drawing shows a block of diamond. Where does
    the light go?




                       ASU PHY112 - Van Tassell -4/16/2007      8
                        Refraction
n   This is called total internal reflection, and is the basis
    for fiber optics.

n   Fiber optics is used in the telephone industry,
    medicine, and a variety of other high tech industries.




                        ASU PHY112 - Van Tassell -4/16/2007      9
                       Refraction
n   Some materials have indices of refraction that are not
    constant, but vary instead with wavelength or
    frequency.

n   In this case red light and blue light would bend by
    different amounts when entering the material.




                       ASU PHY112 - Van Tassell -4/16/2007   10
                      Refraction
n   The result of sending white light incident upon such a
    material would be to have dispersion.

n   Dispersion is the spreading of light into its color
    components by a frequency dependent refraction.

n   Dispersion is the principle behind prisms.



                       ASU PHY112 - Van Tassell -4/16/2007   11
                      Refraction
n   Dispersion is the principle behind prisms.




                       ASU PHY112 - Van Tassell -4/16/2007   12
                       Refraction
n   Dispersion by rain droplets causes rainbows to appear
    in the sky.

n   Each rainbow you see is unique for you as a different
    person, standing at a different location will have light at
    different incident angles, creating a whole different and
    unique rainbow.



                        ASU PHY112 - Van Tassell -4/16/2007   13
                     Mirrors
n Last time we discussed the law of reflection and
  through ray tracing discovered how spherical
  mirrors form images.
n Today we offer an analytical approach to finding
  images produced by spherical mirrors.




                 ASU PHY112 - Van Tassell -4/16/2007   14
                         Mirrors
n   First we define some variables:
    ¨ f=focal length – distance from mirror to where rays
      parallel to the optical axis meet.
    ¨ do=object distance – distance from mirror to object
    ¨ di=image distance – distance from mirror to image
    ¨ m=magnification – the ratio of the height of the
      image ot the height of the object.



                     ASU PHY112 - Van Tassell -4/16/2007    15
                       Mirrors
n   The mirror equation:




n   The magnification equation:




                   ASU PHY112 - Van Tassell -4/16/2007   16
                              Mirrors
n   Sign Conventions:
    ¨ Focal   lengths:
      n + for concave mirrors
      n - for convex mirrors



    ¨ Object   distance
      n + if the object is in front of the mirror (real object)
      n - if the object is behind the mirror (virtual object)



                          ASU PHY112 - Van Tassell -4/16/2007     17
                            Mirrors
n   Sign Conventions:
    ¨ Image   distance:
      n + if the image is in front of the mirror (real image)
      n - if the image is behind the mirror (virtual image)



    ¨ Magnification:
      n + for an image that is upright with respect to the object.
      n - for an image that is upside down with respect to the
        object.


                        ASU PHY112 - Van Tassell -4/16/2007          18
                            Mirrors
n   Example: A 2.0 cm high object is placed 8.3 cm in front of a
    concave mirror whose radius of curvature is 12.0 cm. Find the
    location and description of the image.




                        ASU PHY112 - Van Tassell -4/16/2007         19
                            Mirrors
n   Example: A 2.0 cm high object is placed 8.3 cm in front of a
    concave mirror whose radius of curvature is 12.0 cm. Find the
    location and description of the image.




                        ASU PHY112 - Van Tassell -4/16/2007         20
                            Mirrors
n   Example: A 2.0 cm high object is placed 8.3 cm in front of a
    concave mirror whose radius of curvature is 12.0 cm. Find the
    location and description of the image.

n   Description of the image:
     ¨ The image is real because di>0
     ¨ The image is inverted because m<0
     ¨ The image is enlarged because |m|>1




                        ASU PHY112 - Van Tassell -4/16/2007         21
                             Mirrors
n   Description of images:
    ¨ The image is real if di>0
    ¨ The image is virtual if di<0

    ¨ The image is upright if m>0
    ¨ The image is inverted if m<0

    ¨ The image is reduced if |m|<1
    ¨ The image is enlarged if |m|>1
    ¨ The image is the same size as the object if |m|=1


                         ASU PHY112 - Van Tassell -4/16/2007   22
                              Mirrors
n   Example: A convex mirror is used to reflect light from an object
    placed 60 cm in front of the mirror. The focal length of the mirror
    is f=-46 cm. Find the location and description of the image.




                          ASU PHY112 - Van Tassell -4/16/2007        23
                              Mirrors
n   Example: A convex mirror is used to reflect light from an object
    placed 60 cm in front of the mirror. The focal length of the mirror
    is f=-46 cm. Find the location and description of the image.




                          ASU PHY112 - Van Tassell -4/16/2007        24
                              Mirrors
n   Example: A convex mirror is used to reflect light from an object
    placed 60 cm in front of the mirror. The focal length of the mirror
    is f=-46 cm. Find the location and description of the image.

n   Description of the image:
     ¨ The image is virtual because di<0
     ¨ The image is upright because m>0
     ¨ The image is reduced because |m|<1




                          ASU PHY112 - Van Tassell -4/16/2007        25
                         Mirrors
n   Convex and planar mirrors always produce virtual
    images of real objects.

n   Concave mirrors may produce real or virtual images of
    real objects.




                     ASU PHY112 - Van Tassell -4/16/2007   26
               Now its your turn!
n   A mirror produces an image that is located 34.0 cm
    behind the mirror when the object is located 7.5 cm in
    front of the mirror. What is the focal length of the
    mirror, and is the mirror concave or convex?




                      ASU PHY112 - Van Tassell -4/16/2007    27
                             Mirrors
n   Example: A mirror produces an image that is located 34.0 cm
    behind the mirror when the object is located 7.5 cm in front of
    the mirror. What is the focal length of the mirror, and is the
    mirror concave or convex?




                         ASU PHY112 - Van Tassell -4/16/2007          28

				
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