How Waves Behave


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How Waves Behave

  1. 1. How Waves BehavePowerpoint Templates
  2. 2. Wave Reflection• A reflection occurs when a wave hits a surface and bounces off – All types of waves can be reflected • sound (echoes) • light (mirror images) • water Powerpoint Templates
  3. 3. Angles of Reflection• The incident wave is the source of energy; it shows where the wave is coming from.• The normal is an imaginary line drawn perpendicular to the reflective surface.• Law of reflection: – the angle of incidence (i) is equal to the angle of the reflected wave (r). Powerpoint Templates
  4. 4. Reflection and Sight• How does this woman see her foot in the mirror? – Light reflects off of her foot, hits the mirror, reflects off the mirror, and enters her eyes• The womans brain assumes light travels in a straight line. – Her brain interprets the image as being actually inside the mirror. Powerpoint Templates
  5. 5. Refraction• As waves travel from one medium to another, some waves are reflected (bounce back) and others are refracted ("bent" into a new direction)• Examples: – air to glass to air • Store window – air to glass to water • pencil in water cup – layers of Earth • seismic waves – air to water • The Gar Story Powerpoint Templates
  6. 6. Visualizations of Refraction As a column of marching troops crosses Concrete from a fast medium to a slow medium, the direction of march changes because the first lines of men to reach the "swamp" slow down before the others. Swamp Fast Medium As a toy car rolls from a hard floor onto carpet, it changes direction because the wheel that hits the carpet Slow first is slowed down first. Medium• Refraction occurs when a wave is bent as it passes from one medium into another due to changing wave speed. Powerpoint Templates
  7. 7. Direction of Refraction Fast Medium normal• When a wave refracts into a substance in which it must slow down, the direction will bend towards a line that is perpendicular to the surface that it strikes (the normal).• When waves refract into a substance in which they speed up, the direction will bend away from a line that is perpendicular to the surface that it strikes. Powerpoint Templates
  8. 8. Refraction• Light waves slow down in a denser or more solid medium and speed up with less matter (less dense or less solid). • Sound waves speed up in a denser or more solid medium and slow down the less matter there is (less dense or less solid). • Refraction simulator Powerpoint Templates
  9. 9. Mirage • Light and sound both travel faster in hot air – hot air molecules move faster than cool air, transferring the wave energy along more quickly • Layer of hot air near the ground refracts images of the sky • Your brain assumes light travels in a straight line • Image appears to you as a blue wavy spot on the groundPowerpoint Templates
  10. 10. Diffraction• What happens when waves encounter obstacles in their path? – some waves are reflected – some waves are diffracted (waves change direction as they pass through or around the obstacle) • solid object – boulder in the ocean – radio waves around a building • aperture (opening) – gap in a sea wall – light through a camera f-stop – holes in a musical instrument Powerpoint Templates
  11. 11. Diffraction Around an Object• The amount of direction change (diffraction) around an object depends on two things: – the size of the object • bigger object cause greater diffraction – AND the size of the wavelength (λ) • smaller wavelengths cause greater diffraction • light waves have very small wavelengths so they experience less diffraction than sound or water waves Powerpoint Templates
  12. 12. • When a wave is diffracted, wavelength, frequency, and speed stay the same – ONLY WAVE DIRECTION & AMPLITUDE CHANGE • diffracted sounds are same pitch but not as loud • diffracted light is same color but not as bright • diffracted ocean waves are just as frequent but less high• There is always an area sheltered by waves directly behind the object – waves are less intense, but not absent there – this is why most shadows have a fuzzy edge Powerpoint Templates
  13. 13. Diffraction Through an Aperture• The amount of curving through an opening depends on – the size of the opening (a = aperture) – the relative size of the wavelength (λ) • If opening is larger than wavelength, curving will be minimal. • If the two are equal in size or the opening is smaller than the wavelength, the amount of curving is considerable.• Diffraction is greatest when λ ≥ a. – This happens when: • the aperture is small • the wavelength is large (bigger than aperture) Powerpoint Templates Demo
  14. 14. Useful Diffraction• In a harbor, only a small section of waves is allowed to pass through the walls enclosing the bay. • The waves passing through the gap are spread out (diffracted) into smaller, curved waves.• Any boat or ship floating within the harbor only experiences very small (dissipated) waves, despite that fact that the inner water is exposed to the outside waves through the gap in the harbor wall. Powerpoint Templates
  15. 15. Diffracted Light Powerpoint Templates
  16. 16. Interference• When two waves overlap, interference occurs. – Waves usually originate from different locations, so they often travel in different (even opposite) directions – The resulting wave is the sum of the incoming waves • two crests will add up to create a higher peak: 1 + 1 = 2 • a crest and a trough will cancel each other out: 1 + (-1) = 0 • Constructive Interference – wave are "in phase" – wave forces combine • Destructive Interference – wave are "out of phase" – wave forces cancel out Powerpoint Templates
  17. 17. Examples of InterferenceConstructive Interference Optical interference between two light sources. Destructive Interference• After waves meet and interference occurs, they continue on unaffected. Powerpoint Templates
  18. 18. Resonance• Every object has a natural frequency at which it vibrates – This is determined by: • the objects size & shape • mass of the object • material the object is made out of• Resonance occurs when the frequency of a forced vibration applied to an object matches the objects natural frequency. – a combination of reflection and constructive interference Incident Wave Reflected Wave Resultant Wave Powerpoint Templates
  19. 19. Resonance - a destructive force!• Tacoma Bridge• Wine Glass Breaking• Starfield Concert Floor Collapse Powerpoint Templates