WAVES WAVE INTERACTIONS

FOUR WAYS WAVES INTERACT R-R-D-I REFLECTION REFRACTION DIFFRACTION INTERFERENCE How waves interact with a medium How waves interact with other waves

LAW OF REFLECTION Angle of incidence = angle of reflection

29.2 The Law of Reflection Incident rays and reflected rays make equal angles with a line perpendicular to the surface, called the normal. The angle between the incident ray and the normal is the angle of incidence. The angle between the reflected ray and the normal is the angle of reflection. Angle of incidence = Angle of reflection 4

REFLECTION The bouncing back of a wave when it meets a surface or boundary.

Ordinary paper has a rough surface when viewed with a microscope. 29.4 Diffuse Reflection Diffuse reflection allows us to see most things around us. Light is diffusely reflected from paper in many directions. Light incident on a smooth mirror is only reflected in one direction. Ordinary paper has a rough surface when viewed with a microscope. 6

CONCAVE AND CONVEX MIRRORS

REFRACTION The bending of a wave as it passes from one medium to another. http://www.physicsclassroom.com/mmedia/optics/lr.html Light from pencil moves from air to your eye, through water and glass to your eye, through plastic to your eye

Refraction Examples Light slows down when it goes from air into water and bends toward the normal. An Analogy: A car slows down when it goes from pavement onto gravel and turns toward the normal. An Illusion : Fish in the water appear closer and nearer the surface.

29.8 Refraction of Light As a light wave passes from air into water, its speed decreases. 10

DIFFRACTION The bending of a wave as it passes through an opening or by an edge. Ex.: Hear a voice from around the corner.

31.1 Diffraction and Huygens’ Principle The extent to which the water waves bend depends on the size of the opening. 12

Using diffraction gratings

Doppler Effect The change in frequency of a wave (or other periodic event) for an observer moving relative to its source. It is named after the Austrian physicist Christian Doppler, who proposed it in 1842 in Prague.

Stationary sound source produces sound waves at a constant frequency. Since the source is moving, the center of each new wave is now slightly displaced to the right. As a result, the wave-fronts begin to bunch up on the right side (in front of) and spread further apart on the left side (behind) of the source. An observer in front of the source will hear a higher frequency. Stationary sound source produces sound waves at a constant frequency. http://www.teachertube.com/video/podcast-43-doppler-effect-126074

Wave Interference A phenomenon that occurs when two waves meet while traveling along the same medium.