ch. 25: waves
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Ch. 25: Waves. A WAVE is a rhythmic disturbance that carries energy through matter or space. General Wave Characteristics. Mechanical Waves. Not all waves travel through a medium. Mechanical waves only transfer energy through matter . There are two types: Transverse - PowerPoint PPT PresentationTRANSCRIPT
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Ch. 25: Waves
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A WAVE is a rhythmic disturbance that carries
energy through matter or space
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General Wave Characteristics
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• Not all waves travel through a medium.
• Mechanical waves only transfer energy through matter.
• There are two types:• Transverse• Longitudinal (or compressional)
• Wave motion transfers energy without transferring matter
• Click here for a visual of mechanical waves (at bottom of page)
Mechanical Waves
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Transverse Waves: matter in the medium moves perpendicular to direction the wave travels
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Longitudinal (Compressional) Waves: matter in the medium moves parallel to the direction the wave travels
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Combination Waves: Ocean WaterAn ocean wave is
a combination of transverse and
longitudinal waves.
The individual particles move in
ellipses as the wave disturbance moves toward the shore.
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Concept Check
1. What is a wave?2. What are the two types of
mechanical waves?
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Wave PropertiesThere are four wave properties:
• Amplitude• Frequency
• Wavelength• Wave Velocity
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Amplitude is a measure of the amount of energy in a wave
In Compressional Waves… look at how dense the compressions are. The more dense, the higher the amplitude
In Transverse
Waves…
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Frequency is the number of wavelengths that pass a fixed point each second
f = waves/secondSI unit = Hertz (Hz)As Frequency , WavelengthIs this a high- or low-frequency
wave?
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Wavelength is the distance between a point on one wave and the identical point on the next wave
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Calculating Frequency
F = 1/T Remember T…
Called “period” The time it takes for one wave to pass a
given point Measured in seconds
What is the frequency of ocean waves that wash up on the shore every 2.5 seconds?
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Wave Velocity is how “fast” the wave moves
Velocity = wavelength x frequencyv = λfv = velocity
(m/s)λ = wavelength
(m)f = frequency
(Hz)
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ExampleA sound wave travels from a speaker to your ear. If it has a frequency of 12,000 Hz and a wavelength of 2 cm, what is its velocity?
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Concept Check
List and describe the four wave properties.
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How do waves differ from one another?1) Energy, 2) Velocity, 3) Appearance
TRANSVERSE
COMPRESSIONAL
VS.
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Some other terms to know… Period
Time for one wave to pass a given point (seconds)
Inverse of frequency Node
The point where the medium is never displaced
On the “normal” line Antinode –
The point of maximum displacement Occurs at the wave’s crest
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Standing Waves
NODES
ANTINODES
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Wave Behavior
All waves of all types exhibit these four behaviors: Reflection Refraction Diffraction Interference
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Reflection
The “bouncing back” of a wave
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The Law of Reflection says…
Angle of Incidence = Angle of Reflection
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Refraction The change in wave
direction at the boundary between two different media
Different materials allow waves to travel at different speeds
Angle of Refraction Amount of bending Depends on how much
the material changes the wave’s speed
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DiffractionThe bending of a wave around a barrier or a small
opening
It’s the same process for sound AND light
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Interference When two or more waves (blue and red) exist in the same medium, each wave moves as though the other were absentWhen they meet, they interfere with one another and make a new wave (green).
Visualization of Interference
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Constructive or Destructive? Constructive Interference – 2
waves combine to form a new wave with a larger amplitude.
Destructive Interference – 2 waves combine to produce a wave with a smaller amplitude.
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Wave Formulas f = 1/T
f = frequency (Hz) T = period (s)
v = λ f v = velocity
(m/s) λ = wavelength
(m) f = frequency
(Hz)