Wave Properties Interference

Wave Properties There are 6 main properties, or interactions, of waves that occur when a wave comes in contact with another wave, or a boundary. The 6 Interactions of waves are  Interference  Diffraction  Reflection  Refraction  Absorption  Polarization

Interference When two or more waves combine together.

Superposition principle  There are typically many waves in the same system at the same time.  When more than one wave is present, the total oscillation of any point is the sum of the oscillations from each individual wave.  The sound waves and light waves you experience are the superposition (adding up) of thousands of waves with different frequencies and amplitudes.  Your eyes, ears, and brain separate the waves in order to recognize individual sounds and colors.

Constructive Interference  Constructive interference occurs when waves add up to create a larger amplitude wave.  These waves are in-phase with each other.

Constructive Interference When two waves combine to make a larger wave. (crest & crest) or (trough & trough)

Destructive Interference  Destructive interference occurs when waves add up to make a smaller amplitude wave.  These waves are out-of-phase with each other.

Destructive Interference  Two or more waves combine to produce a smaller wave or destroy the wave completely. (crest & trough)

Check for Understanding! 1. 2.

Results of Interference of Waves  One of the consequences of wave interference is a phenomenon called resonance.  Resonance is the reinforcing of an object’s natural frequency so that the amplitude increases very quickly.  Can you think of something that you have seen or heard that you believe to be caused by resonance?

Standing Waves  A wave that is confined between boundaries is called a standing wave.  With all waves, resonance and natural frequency are dependent on reflections from boundaries of the system containing the wave.  Resonance occurs when the reflected pulses add together to form a large amplitude pulse.

Resonance  Resonance can also occur when one object vibrates another without touching  A sound wave vibrates a snare drum  A singer hits a note that shatters a glass  A struck tuning fork causes another tuning fork of the same frequency to vibrate  The strings of a guitar vibrate from a sound across the room

Resonance

Natural Frequency and Resonance  The natural frequency is sometimes called the resonant frequency because the frequencies are the same when the large amplitudes begin to occur.

Real World Examples: Chinook Helicopter Ground Resonance Test The Tacoma-Narrows Bridge The Tacoma-Narrows Bridge is an example of driven oscillations that result in large amplitude oscillations. Resonance

Today’s Assignment  For your grade today, you and your elbow partner need to find a picture, newspaper article, news report or video of an example of Resonance that I have not already given you.  I will give you 10 minutes to research on your phones or an iPad.  Raise your hand when you are ready to show me and explain your example.  I will come by every group to see what you have done for your grade today!