Introduction to Waves

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Introduction to Waves
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What is a wave?

• It is a disturbance that carries energy through
  matter or space.
• Some require a medium (the matter in which the
  a wave travels)
• Ex) sound requires matter to travel (air, water,
  earth, etc.)
• Some do not require a medium
• Ex) light, radio, and x-rays do not need anything
  to travel.

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Types of Waves

• Mechanical Waves- require a medium
• Almost all waves are mechanical.
• Electromagnetic Waves- dont require a medium.

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Transverse Waves

• Transverse waves have perpendicular motion.
• Light waves travel perpendicularly through space.
• The sine function describes their movement.

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Longitudinal Waves

• Longitudinal waves have parallel motion.
• The wave causes the medium to vibrate in the same
  direction as the wave itself.
• Ex) earthquakes and sound

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Energy Is Involved!!!!

• A wave is a disturbance that carries Energy!
• This is described by its frequency!
• Energy may spread out as a wave travels.
• The higher the frequency, the more energy the
  wave is carrying!

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Wave Characteristics

• Wavelength (?) The distance
• between corresponding
• point on adjacent waves.
• Crest- peak of the wave
• Trough- valley of the wave
• Amplitude- height of the wave from the origin.

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• Frequency (?)
• The number of waves that pass a given point in
  a specific time, usually one second.
• Frequency really describes ENERGY!
• Units for Frequency waves/second  
• Hertz (Hz) 1 wave/second

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Wavelength is Inversely Proportional to Frequency

• A) Wavelength increases (LONG), then frequency
  decreases.
• B) Wavelength decreases (SHORT), then frequency
  increases

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The Electromagnetic Spectrum

• Electromagnetic waves include disturbances in
  electric or magnetic fields and does not require
  a medium.
• Light is one kind of electromagnetic wave.

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Calculating Wave Speed

• wave speed frequency (f) x wavelength (?)
• v f x ?

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Sample problem1 on page 370

• What is the speed of the wave?
• v f x ?
• v (.100 Hz) (15.0 m) 1.50 m/s

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Wave Speed Depends Upon The Medium

• The Kinetic Theory explains this
• Gases molecules are spread far apart and they
  have to travel great distances before they can
  transfer the disturbance of energy to another
  molecule.
• Liquids they are free to slide past one
  another. This allows them to transfer their
  disturbances much more quickly.
• Solids they are tightly packed together and it
  is very easy for vibrations to be passed to one
  another.
• Sound will travel 15 to 20 times faster in rock
  or metal than air.

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Wave Speed Depends Upon The Medium
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Electromagnetic Waves have finite speed

• All electromagnetic waves will travel at the same
  speed in empty space.
• 3 x 108 m/sec
• c- is the symbol that represents speed of light.