Adv Physics(2)

							Adv Physics

Chapter 15
Section 1
Refraction

             If wave strikes
                boundary at a right
                angle the wave
                continues in a
 Air            straight line since all
                parts of the wave
 water          slow at the same
                time by the same
                amount
Refraction

             If wave strikes
                boundary at an angle
                the wave abruptly
                changes direction
 Air            since part of the
                wave is slowed while
 water          part maintains its
                speed
Refraction

  Bending of a wave as it passes from one
   medium to another have a different
   density and a different speed
Refraction
                               Reflected light follows the
 Inc ray           reflected     law of reflection so i = r
                       ray
           i   r               If i > 0 degrees then the
                                   transmitted part is
                                   refracted

                               If i = 0 degrees then the
     normal                        transmitted part travels
                   refracted       straight through and is
                      ray          not refracted
Refraction

             If wave strikes the
                boundary at an angle
                the wave abruptly
                changes direction
 Water          since part of the
                wave is sped up
 air            while part maintains
                its speed
Refraction
  If you travel into a medium where you slow
    down, the light bends toward the normal and
    the angle gets smaller
   i > refraction angle
  If you travel into a medium where you speed
    up, the light bends away from the normal and
    the angle gets bigger
   i < refraction angle
  Exception! If i = 0 degrees (travels along the
    normal) the light doesn’t bend at all
Index of Refraction

  Measure of light’s speed in a medium
  Ratio of the speed of light in a vacuum to
   the speed of light in a medium

   n=c/v

  where n = index, c = speed of light in
  vacuum, v = speed of light in medium
Index of Refraction

 1. Speed of light in water = 2.25 x 108 m/s
    n = c/v = 3 x 108 / 2.25 x 108 = 1.333

 2. Speed of light in glass = 2 x 108 m/s
    n = c/v = 3 x 108 / 2 x 108 = 1.5

 Note: larger the value for n, the slower
    light travels in that medium
Sample Problem

 The light emitted by a He-Ne laser has a
  frequency of 4.74 x 1014 Hz. Find the
  wavelength of the light in a vacuum and
  in ordinary crown glass.
Snell’s Law
  When light travels from a
   material with index n1
   into a material with index
   n2, the angle of
   refraction, Θ2 is related    Θ1
   to the angle of incidence,             n1
   Θ1 by                                  n2

         n1 sinΘ1 = n2 sinΘ2         Θ2
Sample Problem

 A ray of light passes from air into water,
   striking at an angle of 25 degrees with
   the normal. The index of refraction of
   water is 1.333. Calculate the angle of
   refraction of the ray of light.
Sample Problem

 A light ray strikes an air/water surface at an
   angle of 46 degrees with respect to the
   normal. Find the angle of refraction
   when the direction of the ray is a) from air
   to water and b) from water to air.
Sample Problem

 A light ray is incident on the outer surface
   of the cornea at an angle of 40 degrees
   with the normal. Find the angle the
   transmitted ray makes with the normal.
Sample Problem

 A light ray passes from water into ice. If
   the transmitted ray makes an angle of 20
   degrees with the normal, what is the
   angle of incidence.
Sample Problem

 Light travels from air through a flat sheet of
   glass ( n = 1.5 ) into water. If the angle of
   incidence in air is 30 degrees, what is the
   angle of the refracted ray in water?
Sample Problem

 A light ray travels from air to water and
   then is reflected by a mirror under water.
   It strikes the mirror at an angle of 30
   degrees. A) Find the angle of incidence
   as the ray enters the water. B) Find the
   angle of refraction as the ray leaves the
   water.