WAVES

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WAVES

• Physical Science
• Chapter 11

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Vocabulary Chapter 11

• Wave
• Medium
• Mechanical wave
• Electromagnetic wave
• Transverse wave
• Longitudinal wave
• Crest
• Trough
• Amplitude
• Wavelength

• Period
• Frequency
• Wave Speed
• Doppler Effect
• Pitch
• Reflection
• Diffraction
• Refraction
• Interference
• Standing wave

Define these words and study for a vocabulary
test.
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Types of Waves

• Wave A disturbance that caries energy through
  matter or space.
• Medium Matter through which a wave travels.
• Mechanical wave Waves that require a medium to
  pass the energy through.
• Electromagnetic wave (Light, radio, infrared,
  x-ray, etc) Do not need a medium to pass through.
  They are caused by a disturbance in electric and
  magnetic fields.

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Supernumerary rainbow
A rainbow is an example of electromagnetic waves
of visible light. The colors of the spectrum can
be seen in a rainbow. ROYGBIV
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Waves Transfer Energy

• Energy is the ability to do work, so waves carry
  energy and do work.
• Work is done when a force causes a change in
  motion of an object.
• Water waves do work on a leaf, a boat, or on a
  beach. How?
• Sound waves do work on your eardrum. How?
• Light waves do work on your eye or photographic
  film. How?
• Energy may be spread out as a wave travels.
• Each circle of the wave is called a wave front.

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Vibrations and Waves

• Waves are related to vibrations.
• Most waves are created by a vibrating object.
• Electromagnetic waves may be caused by vibrating
  charged particles.
• In mechanical waves, particles in the medium
  vibrate as the wave passes through the medium.

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More on Vibrations

• Simple harmonic motion The motion is periodic,
  as it repeats itself at standard intervals in a
  specific manner

Damped harmonic motion A vibration that fades
out as energy is transferred from one object to
another.
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Transverse and Longitudinal Waves

• Longitudinal waves the particles of the medium
  vibrate parallel to the direction of the wave.
• Sound waves are a good example of a longitudinal
  wave.

• Transverse waves the particles of the medium
  vibrate perpendicular to the direction of the
  wave.
• A good example would be a stadium wave. The
  people would be moving at a right angle to the
  direction of the wave.
• Light waves are transverse waves.
• The electric and magnetic fields are
  perpendicular to the direction the light travels.

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Surface Waves

• Particles move in a circular motion.
• Water waves are an example of a surface wave.
• The particles in a surface wave move both
  perpendicular and parallel to the direction of
  the wave.

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Wave Properties

• All transverse waves have a similar shape. Its
  called a sine curve.
• Waves with this shape are called sine waves.

crest
wavelength
amplitude
wavelength
trough
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Wave properties continued.

• Amplitude the greatest distance that particles
  in a medium move from their normal position.
• Wavelength the distance between two equivalent
  parts of a wave. The symbol is the Greek letter
  Lambda, ?
• Period the time required for one full
  wavelength to pass a certain point. Represented
  by the symbol T, expressed in seconds.
• Frequency the number of waves that pass a given
  point in one second. The symbol for frequency is
  f, it is measured in Hertz. One vibration per
  second is 1Hz.
• f 1/T

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Electromagnetic Spectrum
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Visible Light
Our eyes can detect light with the frequencies
ranging from 4.3 x 1014 Hz to 7.5 x 1014 Hz.
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ROYGBIV WAVES
Cones in our eyes are receivers for these tiny
visible light waves. The Sun is a natural source
for visible light waves and our eyes see the
reflection of this sunlight off the objects
around us. The color of an object that we see is
the color of light reflected. All other colors
are absorbed.
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Wave Speed

• Wave speed is simply how fast a wave moves.
• Recall the formula for speed s d/t
• So the formula for wave speed is as follows
  speed wavelength / period

Or V ? / T
Wave speed can also be calculated by multiplying
frequency times wavelength or V f x ?
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Practice the math
Given Frequency, f 264 Hz Wavelength, ? 1.30
m Unknown wave speed v _______m/s
343
Reverse the formula you just used and show the
formula for frequency. ________
F v / ?
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Wave speed continued.

• The speed of a wave depends on the medium.
• Sound waves travel 340m/s in air.
• They travel 3 to 4 times faster in water.
• Through rock or metal they travel 15 to 20 times
  faster than in air.
• Why???

The arrangement of particles in a medium
determines how well a wave travels through it.
Kinetic theory explains this. Molecules of gases
are further spread apart then liquids or solids.
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The speed of light

• Light has a finite speed.
• 186,000 mi/s
• 3 x 103 m/s
• All electromagnet waves travel at this speed in
  empty space.
• The speed of light is represented by the symbol
  c.
• Light waves will travel slower when passing
  through a medium such as water or air.

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The Doppler Effect

• Pitch how high or low the sound is.
• Pitch is determined by frequency.
• The higher the frequency the higher the pitch and
  vice versa.
• Frequency changes if the source is moving.
• This change in frequency based on movement is
  called the Doppler Effect.

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Wave Interactions

• Reflection The bouncing back of a wave when it
  reaches a surface or boundary.
• Diffraction the bending of waves as they pass
  an edge.
• Refraction The bending of waves as they pass
  from one medium to another.
• Interference when two waves arrive at the same
  location at the same time they combine to form a
  new wave.
• Constructive interference When the crest of one
  wave overlaps the crest of another and they are
  added together to make a larger wave
• Destructive Interference When the crest of a
  large wave meets the trough of another smaller
  wave and they combine by subtraction.

Two waves of the same size may completely cancel
each other out. The amplitudes must be the same.
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Standing Waves

• Standing Wave A wave form caused by
  interference that appears not to move along the
  medium.
• Nodes Regions of no vibration, where crest of
  one wave meets the trough of another and causes
  complete destruction.
• Antinodes Regions of maximum vibration, where
  crests of one wave lines up perfectly with the
  crest of a reflected wave causing maximum
  constructive interference.

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