1. Ch 20 The Energy of Waves
The Nature of Waves

2. The Nature of Waves
Wave- Any disturbance that transmits energy through matter or empty space.
Wave Energy
Energy can be carried away from its source by a wave
Waves transfer energy – NOT MATTER.
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What causes a wave in the first place???? When a source of energy causes a vibration to move through a medium

3. Energy Transfer Through a Medium
Medium- a substance through which a wave can travel.
Can be a solid, liquid, or gas.
When a particle vibrates (moves back and forth) it can pass its energy to a particle next to it.
Some waves don’t need a medium
NEED a Medium
DON’T need a medium
Sound waves
Mechanical waves
Electromagnetic Waves
- Visible Light
- Microwaves
- X rays

4. Types of Waves
Transverse Waves- Waves in which the particles vibrate in an up-and-down motion.
Particles move across, or perpendicular to the direction the wave is going.
Crest- The highest point of a transverse wave.
Trough- The lowest point of a transverse wave (between 2 crests)
( transverse vs. longitundal)

5. Types of Waves
Longitudinal Waves- The particles of the medium vibrate back and forth along the path the wave moves. Particles move parallel to the direction the wave is moving
Compression- A part of a longitudinal wave where the particles are crowded together.
Rarefaction-A part where the particles are spread apart.
Sound waves are longitudinal waves.

6. 1.2 Properties of Waves Amplitude – Height of a wave.
The larger the amplitude is, the taller the wave is.
The larger the amplitude is, the more energy the wave has
From the middle to either the crest or the trough

7. Properties of Waves
Wavelength- distance between a point on one wave and the same point on the next wave
For longitudinal waves, it is the distance between compressions
For transverse waves, it is the distance from crest to crest
The shorter the wavelength the more energy the wave has.

8. Properties of Waves
Frequency- The number of waves produced in a given amount of time.
Expressed in Hertz (Hz)
1 Hz = 1 wave
1 second
Higher frequency means higher energy
In one second, how many waves???
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(when???)
(how old are you?)

9. The period of a wave is the time for a particle on a medium to make one complete cycle.
SI Unit = Seconds (s)
Frequency and period are related Frequency refers to how often something happens . Period refers to the time it takes something to happen
Equation:
p = 1/f
What is the period of a wave that has a frequency of 4 Hz?
What is the frequency of a wave that has a period of 3 seconds?

10. Properties of Waves Wave Speed:
The speed at which the wave travels
V = λ x f
SI Units Speed: m/s Wavelength: m Frequency: Hz
For a wave to move really fast it needs to have a short wavelength and a high frequency
As the frequency increases, and the wavelength decreases
As the wavelength increases, the frequency decreases
Frequency and wavelength are inversely related because as one goes up, the other goes down.
(properties)
(intro)

11. Calculations
Determine the wave speed of a wave that has a wavelength of 5 m and a frequency of 4 Hz.
What is the frequency of a wave if the wave has a speed of 12 m/s and a wavelength of 3 m?
A wave has a frequency of 5 Hz and a speed of 18 m/s. What is the wavelength?

12. How is wavelength related to frequency if the wave is traveling at a constant speed?
How is energy related to the amplitude of a wave?
Describe two ways to measure the wavelength of wave.
If you double the frequency of a wave, what will happen to its wavelength if the speed does not change?

13. Wave Interactions Transmitted Waves
Refraction- The bending of a wave as the wave passes from one medium to another at an angle
Wave speed changes when a wave moves from one medium

14. Refraction of Different Colors
Dispersion- Light rays are spread out into separate colors.
Each color of light has it’s own wavelength.
Diffraction- The bending of waves around a barrier or through an opening that changes its direction

15. Wave Interactions
Interference- Waves occupy the same space at the same time.
Constructive Interference- the crest of one wave overlaps the crest of another wave.
The new amplitude of the combined wave is larger than the original waves
Bridge collapse
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16. The crest of one wave overlaps with the trough of another wave.
Destructive interference- two or more waves combine to produce a wave with a smaller displacement
The crest of one wave overlaps with the trough of another wave.
The new amplitude of the combined wave is smaller than the original waves.
Ex. Noise canceling head phones

17. Constructive & Destructive Interference