Sound and Light

1. Sound and Light Chapter 1: Characteristics of Waves Section 1: What are Waves 3: 38.08/58 = 60.48% 5: 46.05/58 = 79.40% 6: 45.80/58 = 78.97%

2. Wave Energy Medium Mechanical Wave Vibration Transverse wave Crest Trough Longitudinal wave Compression Rarefaction Vocabulary

3. Waves and Energy • A wave is a disturbance that transfers energy from place to place. • Remember, energy is the ability to do work. • Think about a raft on the water • Wave disturbs surface as well as raft. But the disturbance caused by the wave is temporary, and the wave passes, and raft returns to normal. • Most kinds of waves require something to travel though. • The material through which a wave travels is called a medium. • Waves that require a medium are called mechanical waves. • Waves that don’t require a medium are called electromagnetic waves

4. How do waves transfer energy? • Although mechanical waves travel though a medium, they don’t carry the medium with them. • The wave just makes the medium move back and forth, it is the energy that is getting transferred. • Think of the “wave” at a sporting event

5. What causes waves? • Energy is always required to make a wave. • Mechanical waves are produced when a source of energy causes a medium to vibrate. • A vibration is the repeated back and forth or up and down motion. • When a vibration moves through a medium, a wave results. • Remember, anything that moves has energy, so a moving object can give its energy to a medium, and make a wave.

6. Types of Waves • Transverse Waves • Waves that move the medium at right angles to the direction the wave travels. • As a transverse wave moves, the particles of the wave move at right angles to the direction of the wave.

7. Longitudinal Waves • These waves move the medium parallel to the direction in which the wave travels. • Compression is where the medium is close together • Rarefactions are where the medium is far apart.

8. We can use diagrams to represent transverse and longitudinal waves.

9. Sound and Light Chapter 1: Characteristics of Waves Section 2: Properties of Waves

10. Vocabulary • Amplitude • Wavelength • Frequency

11. Amplitude • Remember, all mechanical waves move medium. • The distance the medium moves depends upon the amplitude. • Amplitude is the maximum distance that the particles of the medium carrying the wave move away from their rest positions. • More energy = Greater Amplitude • For transverse waves: Amplitude is the maximum distance up or down the wave moves. • Higher/lower waves = greater amplitude • For longitudinal waves: Amplitude is the measure of how compressed or rarefied the medium becomes. • Dense compressions = greater amplitude

12. Wavelength • Wavelength • A wave travels a certain distance before it starts to repeat. • The distance between two corresponding parts of a wave is the wavelength. • Transverse Wave: Wavelength can be found by measuring distance from crest to crest or from trough to trough. • Longitudinal Wave: Wavelength can be found by measuring distance between compressions.

13. Frequency • Wave frequency is the number of complete waves that pass any given point in a certain amount of time. • If I make waves in a rope so that one wave passes a given point every second, the frequency of the wave is 1 wave per second. • Frequency is measured in unit of hertz (Hz) • The wave above would have a frequency of 1 Hz.

14. Speed of Waves • Different waves travel at different speeds. • The speed of a wave is how far the wave travels in a given length of time • Or the distance divided by the time it took to travel that distance.

15. Relating Ideas • Speed, wavelength and frequency are mathematically related. • Speed = Wavelength x Frequency • Wavelength = Speed / Frequency • Frequency = Speed / Wavelength

16. Sound and Light Chapter 1: Characteristics of Waves Section 3: Interactions of Waves

17. Vocabulary • Reflection • Refraction • Law of reflection • Diffraction • Interference • Constructive Interference • Destructive Interference • Standing wave • Node • Antinode • Resonance

18. Reflection • When a wave hits a surface though which it cannot pass, it bounces back. • This interaction is called reflection • All waves obey this. • The law of reflection states that the angle of incidence equals the angle of reflection.

19. Refraction • When a wave moves from one material to another, it encounters a change in wave speed. • If the wave is at an angle, one side change speed before the other, causing it to bend. • This bending of waves due to a change in speed is called refraction. • Again, the wave MUST enter an angle for this to occur

20. White light and refraction • White light is made of lots of different frequencies of light • When white light refracts, each color bends by different amounts. • This separates the colors • Rainbows!

21. Diffraction • When a wave moves around a barrier or after it passes through a narrow channel it will bend and spread out. • This is called diffraction. • Like refraction, it involves the bending of waves. • Unlike refraction, does not pass through any new materials.

22. Interference • Interference is an interaction that occurs whenever two waves meet. • Two types of interferences • Constructive Interference • Occurs when two waves combine to make a wave with a bigger amplitude • Occurs when crests of one wave overlap with crests of another wave (or troughs and troughs) • Destructive Interference • Occurs when two waves combine to make a wave with a smaller amplitude • Occurs when crests of one wave overlap the troughs of a 2nd wave. • If crest is larger than trough, then resultant wave will have a smaller crest • If trough is larger than crest, the resultant wave will have a smaller trough

24. Interference Applets

25. Standing Waves • A special occurrence when interference occurs after wave reflection has occurred. • If the incoming wave and reflected wave have just the right frequency, they will produce a combined wave that appears to be standing still. • This combined wave is called a standing wave. • So a standing wave is really two waves interfering as they pass through each other, that appears to be standing still.

26. Nodes and Antinodes • In a standing wave, destructive interference produces points with no amplitude. • These points of zero amplitude on a standing wave are called nodes. • Nodes are always evenly spaced on the standing wave. • Also in a standing wave, constructive interference creates points with great amplitude. • These points of maximum amplitude are called antinodes. • Antinodes are also ½ between nodes.

27. Standing Wave Demonstrator

29. Resonance • Most object have a natural frequency. • A swing that is pushed at the swing’s natural frequency allows a small push to create a large increase in the swing’s amplitude. • Standing waves occur when an object vibrates at its natural frequency. • If a nearby object vibrates at the same frequency as an object’s natural frequency, resonance can occur. • Resonance is an increase in the amplitude of a vibration that occurs when external vibrations match an object’s natural frequency. • Can be useful • Musical instruments use resonance o create stronger, clearer sounds.

30. Resonance can be harmful • Tacoma Narrows Bridge