1. Ch. 25: Waves

2. A WAVE is a rhythmic disturbance that carries energy through matter or space

3. General Wave Characteristics

4. Mechanical Waves 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)

5. Transverse Waves: matter in the medium moves perpendicular to direction the wave travels

6. Longitudinal (Compressional) Waves: matter in the medium moves parallel to the direction the wave travels

7. Combination Waves: Ocean Water
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.

8. Concept Check What is a wave?
What are the two types of mechanical waves?

9. Wave Properties There are four wave properties: Amplitude Wavelength
Frequency
Wave Velocity

10. Amplitude is a measure of the amount of energy in a wave
In Transverse Waves…
In Compressional Waves… look at how dense the compressions are. The more dense, the higher the amplitude

11. Frequency is the number of wavelengths that pass a fixed point each second
f = waves/second
SI unit = Hertz (Hz)
As Frequency ,
Wavelength
Is this a high- or low-frequency wave?

12. Wavelength is the distance between a point on one wave and the identical point on the next wave

13. 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?

14. Velocity = wavelength x frequency
Wave Velocity is how “fast” the wave moves
Velocity = wavelength x frequency
v = λf
v = velocity (m/s)
λ = wavelength (m)
f = frequency (Hz)

15. Example
A 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?

16. List and describe the four
Concept Check
List and describe the four
wave properties.

17. How do waves differ from one another?
1) Energy, 2) Velocity, 3) Appearance
TRANSVERSE
VS.
COMPRESSIONAL

18. 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

19. Standing Waves
ANTINODES
NODES

20. Wave Behavior All waves of all types exhibit these four behaviors:
Reflection
Refraction
Diffraction
Interference

21. The “bouncing back” of a wave
Reflection
The “bouncing back” of a wave

22. The Law of Reflection says… Angle of Incidence = Angle of Reflection

23. 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

24. Diffraction The bending of a wave around a barrier or a small opening
It’s the same process for sound AND light

25. 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

26. 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.

27. Wave Formulas f = 1/T v = λ f f = frequency (Hz) T = period (s)
v = velocity (m/s)
λ = wavelength (m)
f = frequency (Hz)