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15.3

15.3. Interactions of Waves. Reflection. When an object/wave hits a surface through which it cannot pass, it bounces back, which is called reflection Reflection is a common occurrence in our everyday lives

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15.3

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  1. 15.3 Interactions of Waves

  2. Reflection • When an object/wave hits a surface through which it cannot pass, it bounces back, which is called reflection • Reflection is a common occurrence in our everyday lives • All waves obey the law of reflection which states that the angle of incidence equals the angle of reflection Angle of reflection Angle of incidence Incoming Wave Reflected Wave

  3. Refraction • Have you ever been in the car and a tire has gone off the side of the road? How easy is it to maintain a straight line? • Changes in speed can cause waves to change direction • When a wave enters a new medium at an angle, one side of the wave changes speed before the other side, causing the wave to bend • The bending of waves due to a change in speed is called refraction • A wave does not always bend when entering a new medium; it only bends if it enters the new medium at an angle • Bending occurs because the 2 sides of the wave are travelling at different speeds

  4. Diffraction and Interference • When a wave moves around a barrier or through an opening in a barrier, it bends and spreads out • This type of wave interaction is diffraction

  5. What happens when 2 solid objects collide? • Unlike solid objects, waves can overlap when they meet • This type of interaction is called interference: constructive and destructive • Constructive interference takes place when waves combine to make a wave with a larger amplitude • Destructive interference takes place when 2 waves combine to make a wave with a smaller amplitude

  6. Standing Wave • When an incoming wave and a reflected wave seem to have just the right frequency, the will produce a combined wave that appears to be standing still • A standing wave is one that appears to stand in one place, even though it is really 2 waves interfering with each other • In a standing wave, destructive interference produces points of amplitude at zero; this zero amplitude point is called a node and they are evenly spaced out along the wave • Where constructive interference occurs, the amplitude is greater than zero; the points of maximum amplitude is an antinode • Antinodes are points of maximum energy and always occur halfway between 2 nodes

  7. Resonance • Most objects have a natural frequency of vibrations • Standing waves occur in objects when it vibrates at a natural frequency • If a nearby object vibrates at the same frequency, it can cause resonance which is an increase in the amplitude of a vibration that occurs when external vibrations match an object’s natural frequency • Resonance can be both useful and harmful • It is useful in musical instruments to produce stronger, clearer sounds • It can be harmful in the instance of an earthquake in which the frequency of earthquake waves match the natural frequency of the ground causing damage to buildings due to resonance

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