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Objectives Describe reflection, refraction, diffraction, and interference.

Compare destructive interference with constructive interference.

Describe resonance, and give examples.Section 3 Wave InteractionsChapter 221

Reflection Reflection happens when a wave bounces back after hitting a barrier.

Light waves reflecting off an object allow you to see that object. A reflected sound wave is called an echo.

Waves are not always reflected when they hit a barrier. A wave is transmitted through a substance when it passes through the substance.Section 3 Wave InteractionsChapter 222

Chapter 22http://www.acoustics.salford.ac.uk/schools/teacher/lesson3/flash/whiteboardcomplete.swf

Chapter 22

Refraction Refraction is the bending of a wave as the wave pass from one medium to another at an angle.

When a wave moves from one medium to another, the waves speed and wavelength changes. As a result, the wave bends and travels in a new direction.Section 3 Wave InteractionsChapter 225

Chapter 22http://www.acoustics.salford.ac.uk/schools/teacher/lesson3/flash/whiteboardcomplete.swf

Chapter 22

Diffraction Diffraction is the bending of waves around a barrier or through an opening.

The amount of diffraction of a wave depends on its wavelength and the size of the barrier or opening the wave encounters.Section 3 Wave InteractionsChapter 228

Chapter 22http://www.acoustics.salford.ac.uk/schools/teacher/lesson3/flash/whiteboardcomplete.swfChapter 22

Section 3 Wave Interactions

Chapter 2211

Interference, continued Standing Waves are waves that appear to be standing still. A standing wave only looks as if it is standing still. Waves are actually going in both directions.

In a standing wave, certain parts of the wave are always at the rest position because of total destructive interference. Other parts have a large amplitude because of constructive interference.Section 3 Wave InteractionsChapter 2212

Interference, continued The frequencies at which standing waves form are called resonant frequencies.

Resonance happens when an object vibrating at or near the resonant frequency of a second object causes the second object to vibrate.

An example of resonance is shown on the next slide.Section 3 Wave InteractionsChapter 2213http://www.youtube.com/watch?feature=player_detailpage&v=xox9BVSu7Okhttp://www.youtube.com/watch?v=oXV45t6wlWUChapter 22