Download - Ch. 25: Waves A WAVE is a rhythmic disturbance that carries energy through matter or space
Ch. 25: Waves
A WAVE is a rhythmic disturbance that carries
energy through matter or space
General Wave Characteristics
• 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
Transverse Waves: matter in the medium moves perpendicular to direction the wave travels
Longitudinal (Compressional) Waves: matter in the medium moves parallel to the direction the wave travels
Combination Waves: Ocean Water
An ocean wave is a combination of transverse and
longitudinal waves.
An ocean wave is a combination of transverse and
longitudinal waves.
The individual particles move in
ellipses as the wave disturbance moves toward the shore.
The individual particles move in
ellipses as the wave disturbance moves toward the shore.
Concept Check
1. What is a wave?
2. What are the two types of mechanical waves?
Wave PropertiesThere are four wave properties:
• Amplitude• Frequency
• Wavelength• Wave Velocity
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…
Frequency is the number of wavelengths that pass a fixed point each second
f = waves/second
SI unit = Hertz (Hz)As Frequency ,
WavelengthIs this a high- or low-frequency wave?
Wavelength is the distance between a point on one wave and the identical point on the next wave
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?
Wave Velocity is how “fast” the wave moves
Velocity = wavelength x frequencyv = λfv = velocity
(m/s)λ = wavelength
(m)f = frequency
(Hz)
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?
Concept Check
List and describe the four wave properties.
How do waves differ from one another?1) Energy, 2) Velocity, 3) Appearance
TRANSVERSE
COMPRESSIONAL
VS.
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
Standing Waves
NODES
ANTINODES
Wave Behavior
All waves of all types exhibit these four behaviors: Reflection Refraction Diffraction Interference
Reflection
The “bouncing back” of a wave
The Law of Reflection says…
Angle of Incidence = Angle of Reflection
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
DiffractionThe bending of a wave around a barrier or a small
opening
It’s the same process for sound AND light
Interference When two or more waves (blue and red) exist in the same medium, each wave moves as though the other were absent
When they meet, they interfere with one another and make a new wave (green).
Visualization of Interference
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.
Wave Formulas
f = 1/T f = frequency (Hz) T = period (s)
v = λ f v = velocity
(m/s) λ = wavelength
(m) f = frequency
(Hz)