Ch29_IrwinA

**__PC Summary Lesson 1__**
Light exhibits certain behaviors that are characteristic of any wave and would be difficult to explain with a purely particle-view. Light reflects in the same manner that any wave would reflect. Light refracts in the same manner that any wave would refract. Light diffracts in the same manner that any wave would diffract. Light undergoes interference in the same manner that any wave would interfere. And light exhibits the Doppler effect. All waves are known to undergo reflection or the bouncing off of an obstacle. All waves are known to undergo refraction when they pass from one medium to another medium. Refraction of waves involves a change in the direction of waves as they pass from one medium to another. And diffraction involves a change in direction of waves as they pass through an opening or around an obstacle in their path. Water waves have the ability to travel around corners, around obstacles and through openings. Wave interference is a phenomenon that occurs when two waves meet while traveling along the same medium. Constructive interference occurs at any location along the medium where the two interfering waves have a displacement in the same direction. Destructive interference occurs at any location along the medium where the two interfering waves have a displacement in the opposite direction. The antinodes (points where the waves always interfere constructively) seem to be located along lines - creatively called antinodal lines The nodes also fall along lines - called nodal lines. The two-point source interference pattern is characterized by a pattern of alternating nodal and antinodal lines. A two-point source interference pattern always has an alternating pattern of nodal and antinodal lines. Any type of wave, whether it be a water wave or a sound wave should produce a two-point source interference pattern if the two sources periodically disturb the medium at the same frequency. Coherent light is when two light waves are vibrating in phase with each other. Light wave interference results when two waves are traveling through a medium and meet up at the same location. When a wave (light waves included) reaches the boundary between two media, a portion of the wave reflects off the boundary and a portion is transmitted across the boundary. The reflected portion of the wave remains in the original medium. The transmitted portion of the wave enters the new medium and continues traveling through it until it reaches a subsequent boundary. If the new medium is a thin film, then the transmitted wave does not travel far before it reaches a new boundary and undergoes the usual reflection and transmission behavior. Thus, there are two waves that emerge from the film - one wave that is reflected off the top of the film (wave 1 in the diagram) and the other wave that reflects off the bottom of the film (wave 2 in the diagram).

**__PC Summary Lesson 3__**
A naming and numbering system is used to refer to these antinodal and nodal lines. An antinodal line extends outward from the sources in the exact center of the pattern. This antinodal line is referred to as the central antinodal line. More antinodal lines are present to the left and to the right of the central antinodal line. These are referred to as the first antinodal line, the second antinodal line, the third antinodal line (if present), etc. Each antinodal line is separated by a nodal line. The nodal lines are also named; the first nodal line to the left or to the right of the central antinodal line is referred to as the first nodal line. The second nodal line and the third nodal line are found as one moves further to the left and to the right of the center of the pattern. Each line in the pattern is assigned a number, known as the order number and represented by the letter m.