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Chapter 15: Waves

Chapter 15: Waves. Section 3: Waves behave in predictable ways. When waves encounter a new medium, one of three things can happen: Reflection Refraction diffraction. Reflection. This is what occurs when waves meet a new barrier that they can’t move through.

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Chapter 15: Waves

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  1. Chapter 15: Waves Section 3: Waves behave in predictable ways.

  2. When waves encounter a new medium, one of three things can happen: • Reflection • Refraction • diffraction

  3. Reflection • This is what occurs when waves meet a new barrier that they can’t move through. • When a wave meets a medium that it can’t travel through (a barrier), the wave exerts a force on the barrier. • Newton’s third law causes the barrier to push the wave back in the opposite direction. This is reflection.

  4. Examples of reflection • Your reflection in the mirror • Sound reflecting back from a sound shell during a concert • An echo reflecting back to you • Waves crashing against the side of a ship

  5. Refraction • This occurs when a wave changes from one medium to another. • Because waves travel at different speeds in different mediums, the wave bends, or refracts, when it enters the new medium. • Ex: straw in a glass of water

  6. Diffraction • Occurs when waves travel through an opening in a barrier. • After the waves go through the barrier, they spread out in all directions. • Also occurs when waves spread out to go around the sides of a barrier.

  7. Interference • Occurs when two waves meet and combine. • Two types of interference: • Constructive • destructive

  8. Constructive Interference • Occurs when two waves coming from different directions temporarily come together. Their crests and trough have to ‘match up’. • Look at the example in your book on page 507. • When constructive interference occurs, the amplitudes of the two waves are added together to make one wave that has twice the amplitude. • A larger wave is CONSTRUCTED

  9. Destructive Interference • Occurs when two very similar waves meet and the crest of one matches up with the trough of the other. • This causes the resulting wave to be smaller. • If the two waves with the same amplitude match up perfectly (crest to trough), then the energy of the waves will cancel each other out (the wave will be destroyed). • Look at the diagram on pg. 508. • Also look at the bottom left corner of the photo on pg. 508.

  10. http://id.mind.net/~zona/mstm/physics/waves/interference/waveInterference2/WaveInterference2.htmlhttp://id.mind.net/~zona/mstm/physics/waves/interference/waveInterference2/WaveInterference2.html • http://www.brainpop.com/science/energy/refractionanddiffraction/quiz/

  11. Model of a wave • Use craft materials to construct a transverse OR a longitudinal wave. • Label the parts of the wave • Transverse wave: crest, trough, amplitude, wavelength, resting point • Longitudinal wave: compression, rarefaction, wavelength

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