Interactions of Waves Chapter 11.3

Reflection Reflection occurs when an object or a wave hits a surface through which it cannot pass, and it bounces back Examples: Shouting in an empty gym Looking in a mirror The law of reflection: the angle of incidence equals the angle of reflection

The Law of Reflection Angle of reflection= Angle of incidence

Free end and Fixed end reflection

Refraction Bending occurs because the two sides of the wave are traveling at different speeds Examples: Seeing a rainbow Trying to grab an object underwater The bending of waves due to changes in speed is called refraction Refraction occurs when a wave enters a new medium at angle, one side of the wave changes speed before the other side, causing the wave to bend

What are the two mediums the straw has entered?

Diffraction Diffraction occurs when a wave bends around a barrier or passes through an opening in a barrier, it bends and spreads out

Interference Two waves can overlap when they meet Interference is the interaction between waves when they meet There are two types of Interference 1. Constructive Interference 2. Destructive Interference

Constructive Interference Constructive Interference occurs when waves combine to make a wave with a larger amplitude When crests from each wave meet, constructive interference makes a higher crest in the area of overlap The amplitude of this crest is the sum of the amplitude of the two original crests After the waves pass through each other they continue on as if they had never met

Destructive Interference Destructive Interference occurs when two waves combine to make a wave with a smaller amplitude Can be thought of as subtracting energies Destructive interference occurs when the crest of one wave overlaps the trough of another wave If the crest has a larger amplitude than the trough, the crest wins and part of it remains If the original trough has the larger amplitude the result is a trough If the original waves have equal amplitudes then the crest and trough completely cancel out

Standing Waves Occurs when an incoming wave and reflected wave have just the right frequency, and they produce a wave that appears to be standing still A standing wave appears to be standing in one place, but in reality it is really two waves interfering as they pass

Nodes and Antinodes Nodes are points of zero amplitude produced by destructive interference of standing waves Nodes are always evenly spaced along a wave Antinodes are points of maximum amplitude on a standing wave created by constructive interference Antinodes are also the points of maximum energy on the wave Antinodes occur halfway between nodes

Resonance Most objects have at least one natural frequency of vibration If a nearby object vibrates at the same frequency it can cause resonance Resonance is an increase in the amplitude of a vibration that occurs when external vibrations match an object’s natural frequency Resonance can be useful Example: musical instruments use resonance to produce stronger, clearer sounds Resonance can be harmful Earthquakes (Mexico City Earthquake of 1985)