Waves

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Waves
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Waves

• Wave a disturbance that transfers energy from
  place to place.
• Medium the material through which the wave can
  pass.
• Waves are classified by
• 1. the way they move.
• 2. the medium through which the wave can pass.

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Transverse waves

• Particles of the medium move
• perpendicular to the direction of wave
  motion.
• (looks like a jump rope)
• 2. Can travel through liquids, gases, empty space
  and SOME solids.
• Ex) Ocean waves

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Longitudinal Waves

• Particles of the medium move parallel
• to the direction of wave motion.(looks like a
  slinky)
• Ex) sound and water

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Wave Components
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Crest

• Crest - maximum positive distance from the rest
  position, top of the wave
• Peak

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Trough

• Crest - maximum positive distance from the rest
  position, bottom of the wave
• Valley

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Amplitude

• Amplitude - the height of the wave, either rest
  position to crest or rest position to trough
• Amplitude is 1/2 the total displacement
• Tells the strength, power, intensity of a wave
• Ex sound - volume, light - brightness,
  earthquakes - power
• Units Meters

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Wavelength

• Wavelength - the distance from one corresponding
  point on a wave to the same point on the next
  wave
• Crest to crest, or trough to trough
• Units are Meters

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Frequency

• Frequency - the number of waves that pass a fixed
  point in a given amount of time
• Greater frequency, greater the energy
• Units are waves per second, Hertz (Hz)

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Velocity

• Velocity - the speed and direction of the wave,
  distance divided by time
• Units are m/s
• The velocity of a wave changes in every new
  medium it enters
• Medium - the material a wave is traveling through
• Sound travels at 343 m/s and light at
  300,000,000 m/s

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Wave Formula

• Wave formula
• v f x w
• Velocity frequency x wavelength
• Ex A wave traveling at 3.0x108 m/s has a
  frequency of 10,000Hz. What is the wavelength of
  the wave?
• 3.0x108 m/s 10,000Hz x w
• w 3.0x108 m/s / 10,000Hz 30,000m

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Reflection

• Reflection - waves strike a surface they reflect
  and invert.
• Ex Sonar - sound, radar - radio waves, echoes
  for sound, satellites

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Part 2 - Reflection

• Reflection from a mirror

Normal
Reflected ray
Incident ray
Angle of reflection
Angle of incidence
Mirror
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Seeing color

• The color an object appears depends on the colors
  of light it reflects.

For example, a red book only reflects red light
White light
Only red light is reflected
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A pair of purple trousers would reflect purple
light (and red and blue, as purple is made up
of red and blue)
Purple light
A white hat would reflect all seven colours
White light
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A pair of purple trousers would reflect purple
light (and red and blue, as purple is made up
of red and blue)
Purple light
A white hat would reflect all seven colours
White light
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• In different colours of light this kit would look
  different

Red light
Shirt looks red
Shorts look black
Shirt looks black
Blue light
Shorts look blue
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Refraction

• Refraction - waves bend when entering a new
  medium, the change in density causes the wave to
  change speed
• Ex Pencil bends in water, fish look bigger in
  water

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Diffraction

• Diffraction - waves bend around an obstacle in
  their path
• Ex sound can bend around corners, light can fan
  out through small openings

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Interference

• Interference - two or more waves traveling in the
  same medium can interact. They can reinforce each
  other called constructive interference (in-phase)
  or oppose each other called destructive
  interference (out-of-phase)
• Ex Waves can add or subtract to form a new wave
  (Rogue wave in ocean)

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The Doppler Effect

• Doppler Effect - change in frequency of a wave
  based on the motion of the source or observer
• the frequency of a wave appears higher when
  approaching and lower when moving away from the
  observer
• Works for all waves

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Doppler Effect - Sound

• Sounds appear higher in frequency (pitch) when
  approaching and lower when moving away
• Ex 1 - An police siren sounds higher frequency
  (pitch) when approaching and lower when moving
  away

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Doppler Effect - Light

• Light appears higher in frequency (closer to
  purple) when approaching and lower (closer to
  red) when moving away
• Ex 2 - Light appears higher frequency when
  approaching (Blue-Shift) and lower frequency when
  moving away (Red-Shift). Hubble proved the
  universe is expanding because light is shifted
  towards the red frequencies.

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Sound

• Sound - mechanical wave caused by objects
  vibrating, which compresses and expands air
  molecules
• Speed of sound increases with temperature

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Sound - Compressional

• Compressional (longitudinal) wave, moves faster
  through dense objects, cant go through a vacuum

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The Ear
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The Electromagnetic Spectrum

• Electromagnetic waves - energy caused by
  vibrating charged particles such as electrons
• All move the speed of light 3.0 x 108m/s
• Can travel through nothing at all (vacuum), and
  go faster through less dense mediums
• Are ordered based on energy, frequency, and
  wavelength
• Order radio, microwaves, infrared (heat),
  visible light, ultraviolet, x-rays, and gamma
• ROYGBIV are the colors of visible light

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Electromagnetic continued

• Energy of electromagnetic waves are electron
  volts (eV)
• We only see the colors of visible light, but many
  of the other waves can be detected with special
  instruments, some animals dont see with visible
  light (insects, reptiles)
• Overexposure to the waves higher in energy than
  visible light (UV, x-ray, and gamma) can be
  harmful causing cancer and genetic mutations
• Electromagnetic energy is often aborbed into heat

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Daily Quiz

• Questions 1-5 labels the parts of the wave on
  the board
• 6. What is it called when a wave bends in a new
  medium?
• 7. What is it called when a wave bounces off a
  surface?
• 8. What is it called when a wave bends around an
  obstacle?

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Daily Quiz

• 9. What part of the wave tells you the intensity
  of the wave?
• 10. What is the length of the wave called?
• 11. What is the number of waves per second
  called?
• 12. What are the units for wavelength?
• 13. What are the units for frequency?

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Daily Quiz

• 14. Which type of wave vibrates parallel to the
  direction it travels?
• 15. Which type of wave vibrates perpendicular to
  the way it travels?
• 16. True or False. Sound is produced by vibrating
  objects.
• 17. True or False. Sound can travel through a
  vacuum.
• Bonus 1 - What is the change in frequency called
  when an object approaches and leaves/
• Bonus 2 - What does Mach 2 mean (Think sound)?