 Simply put, “Refraction” means bends.  When discussing light beams, light bends when it goes from one medium (glass, water, air, etc.) to another.  If it goes from a more dense medium to a less dense medium, then light speeds up and bends away from the Normal.  If it goes from a less dense medium to a more dense medium, then light slows down and bends towards the Normal.  Consider the wheel and axel to the right.  It rolled from pavement (less dense) to gravel (more dense)  The left wheel slowed down causing the axel to turn towards the normal. Pavement Gravel Refraction

 When light undergoes refraction while traveling from a less dense to a more dense medium, the light bends towards the normal.  This is because light travels faster in a less dense medium than in a more dense medium.  Is the fish safe from the laser if we point the laser at the fish?  As a result, the light will bend and travel below the fish.  This bending of light at the interface of two mediums is known as refraction. Normal

Refraction  Which of the three paths (A, B, or C) is the one the beam would actually travel?  Remember, lights bends towards the normal when it goes from a less dense to a more dense medium because it slows down in the more dense medium.  Which is the correct path? A B C Air Glass Water

Snell’s Law  Snell’s law allows us to determine the angle of refraction given the angle of incidence of a light ray on a boundary interface.  Based upon the picture to the right, which medium us more dense: 1 or 2? Why?  Because medium 2 is more dense n 2 >n 1. n 1 sin  1 = n 2 sin  2 n1n1 n2n2

Internal Reflection  Suppose we had a laser submerged in water.  If it was pointing straight up, then the beam would pass through the boundary interface without reflecting or refracting.  If we rotate the laser, then some of the beam will reflect and some will refract.  As we continue to rotate the laser, we would eventually observe the refracted beam traveling along the boundary interface.  This phenomena occurs at the critical angle.  As the laser is rotated past the critical angle, all of the beam will be reflected and none will be refracted.  This phenomena is known as total internal reflection

Refraction  Refraction applies to Lenses as well.  Which laser path to the right would the laser beam follow?  When the beam first strikes the lens, it goes from a less dense to a more dense medium.  As a result, the beam will slow down and turn towards the normal.  It will stay on the same side of the normal.  Note that when the beam is back in the original medium it is parallel to the original beam.

Lens Vocabulary  C – Center of Curvature  B – Focal Point  f – Focal Length  D – Principal Axis CCBB ff D 18-18

Reflection  Observe the reflection of a laser beam due to the mirror.  The Normal is an imaginary line drawn at a 90  angle with the surface of the mirror at the point where the beam strikes the mirror.  The angle between the incident ray and the normal is known as the angle of incidence (  i ).  The angle between the reflected ray and the normal is known as the angle of reflection (  r ) Mirror Incident RayReflected Ray Normal

23.3 Formation of Images by Spherical Mirrors Geometrically, we can derive an equation that relates the object distance, image distance, and focal length of the mirror: (23-2)

23.3 Formation of Images by Spherical Mirrors We can also find the magnification (ratio of image height to object height). (23-3) The negative sign indicates that the image is inverted. This object is between the center of curvature and the focal point, and its image is larger, inverted, and real.

Diffuse Scattering.  Imagine that several parallel laser beams are fired at a mirror and a ceiling tile.  The reflected beams from the mirror surface would still be parallel, and  i and  r would be equal.  However, the reflected beams from the tile surface would not be parallel.  The reflected beams from the tile surface exhibit diffuse scattering Mirror Ceiling Tile