1. Chapter 20
Waves

2. Section 1: Objectives
Describe how waves transfer energy without transferring matter.
Distinguish between waves that require a medium and waves that do not.
Explain the difference between transverse and longitudinal waves.

3. Wave Energy
A wave is any disturbance that transmits energy through matter or empty space.
Energy can be carried away from its source by a wave.
The material through which the wave travels does not move with the energy.

4. Wave Energy

5. Wave Energy As a wave travels, it does work on everything in its path.
The waves in a pond do work on the water to make it move up and down.
The waves also do work on anything floating on the water’s surface.
The fact that the water and floating objects move tells you that the waves are transferring energy.

6. Wave Energy
Most waves transfer energy by the vibration of particles in a medium.
A medium is a substance through which a wave can travel.
Sound waves, water waves, and seismic waves all need a medium through which to travel.

7. Wave Energy
Visible light waves, microwaves, radio waves, and X rays are examples of waves that can transfer energy without going through a medium.
These waves are electromagnetic waves.
Electromagnetic waves do not require a medium like other waves.

8. Wave Energy
Transverse Waves are waves in which the particles vibrate perpendicularly to the direction the wave is traveling.
Transverse waves are made up of crests and troughs.
Water waves, waves on a rope, and electromagnetic waves are examples of transverse waves.

9. Wave Energy
Longitudinal Waves are waves in which the particles vibrate back and forth along the path that the waves moves.
Longitudinal waves are made up of compressions and rarefactions.
Waves on a spring are longitudinal waves.

10. Wave Energy

11. Wave Energy
Sound Waves are longitudinal waves. Sound waves travel by compressions and rarefactions of air particles, as shown below.

12. Wave Energy
Combinations of Waves A transverse waves and a longitudinal wave can combine to form a surface wave.
Surface waves look like transverse waves, but the particles of the medium move in circles rather than up and down.

13. Wave Energy

14. Chapter 20 Sec. 1 Pop Quiz
1) T/F Energy can’t be carried away from its source by a wave.
2) T/F As a wave travels it does work on the path.
3) How do most waves transfer energy?
4) List 1 type of wave that does not require a medium to pass through.
5) What is the difference between transverse and longitudinal waves?
6) What is a surface wave?

15. Section 2: Objectives Identify and describe four wave properties.
Explain how frequency and wavelength are related to the speed of a wave.

16. Parts Of A Wave
The amplitude of a wave is the maximum distance that the particles of a medium vibrate from their rest position.
A wave with a large amplitude carries more energy than a wave with a small amplitude.

17. Parts Of A Wave
A wavelength is the distance between any point on a wave to an identical point on the next wave.
A wave with a shorter wavelength carries more energy than a wave with a longer wavelength does.

18. Parts Of A Wave
Frequency is the number of waves produced in a given amount of time.
Frequency is usually expressed in hertz (Hz).
One hertz equals one wave per second.
If the amplitudes are equal, high- frequency waves carry more energy than low-frequency waves.

19. Parts Of A Wave

20. Parts Of A Wave
Wave Speed is the speed at which a wave travels.
Wave speed (v) can be calculated using wavelength () and frequency (f), by using the wave equation, which is shown below:
v    f

21. Calculating Wavelength

22. Example # 1 Remember: v    f
What is the frequency of a wave if the wave has a speed of 12 cm/s and a wavelength of 3 cm?
Remember: v    f
 = v / f (Rearranged by dividing by f)
F = V /  (Rearranged by dividing by )

23. Example # 2 Remember: v    f
A wave has a frequency of 5 Hz and a wave speed of 18 m/s. What is the wavelength?
Remember: v    f
 = v / f (Rearranged by dividing by f)
F = V /  (Rearranged by dividing by )

24. Parts of A Wave Frequency and wavelength are inversely related.
So, if one value is doubled, the other value will be cut in half.
The wave speed of a wave in a certain medium is the same no matter what the wavelength is.
So, the wavelength and frequency depend on the wave speed, not the other way around.

25. Chapter 20 Sec. 2 Pop Quiz
1) What is the unit used to measure frequency?
2) What is 1 Hz equal to?
3) What is the formula used to calculate wave speed?
4) How are frequency and wavelength related?
5) What will happen to the speed of a wave in a certain medium if the wavelength changes?

26. Section 3: Objectives
Describe reflection, refraction, diffraction, and interference.
Compare destructive interference with constructive interference.
Describe resonance, and give examples.

27. Wave Angles
Reflection happens when a wave bounces back after hitting a barrier.
Light waves reflecting off an object allow you to see that object.
A reflected sound wave is called an echo.
Waves are not always reflected when they hit a barrier.
A wave is transmitted through a substance when it passes through the substance.

28. Wave Angles
Refraction is the bending of a wave as the wave pass from one medium to another at an angle.
When a wave moves from one medium to another, the wave’s speed and wavelength changes.
As a result, the wave bends and travels in a new direction.

29. Wave Angles
Diffraction is the bending of waves around a barrier or through an opening.
The amount of diffraction depends on its wavelength and the size of the barrier or opening the wave encounters.

30. Wave Angles
Interference is the result of two or more waves overlapping.
Constructive Interference happens with the crests of one wave overlap with the crests of another wave or waves. The troughs of the waves also overlap.
Constructive Interference results in a new wave that has a larger amplitude than the original waves had.

31. Wave Angles
Destructive Interference happens with the crests of one wave and the troughs of another wave overlap.
Destructive interference results in a new wave that has a smaller amplitude than the original waves had.
When the waves involved in destructive interference have the same amplitude and meet each other at just the right time, the result is no wave at all.

32. Wave Angles

33. Wave Angles Standing Waves are waves that appear to be standing still.
A standing wave only looks as if it is standing still.
Waves are actually going in both directions.
In a standing wave, certain parts of the wave are always at the rest position because of total destructive interference.
Other parts have a large amplitude because of constructive interference.

34. Wave Angles
The frequencies at which standing waves form are called resonant frequencies.
Resonance happens when an object vibrating at or near the resonant frequency of a second object causes the second object to vibrate.