Unit 2 : WavesUnit 2 : Waves

Hmmmm . . .

TOD: IN•Write a brief description in your composition book of what you think a wave is.

•Then write a short paragraph describing a time you might have experienced waves.

Objectives (things you just might learn)

• Describe how vibrations in materials set up wave disturbances that spread away from the source.

• Distinguish between waves that require a medium and waves that do not.

• Explain the difference between transverse and longitudinal waves.

Waves and Energy

• A wave is any disturbance that transmits energy through matter or empty space.

• The energy passed along by a wave moves farther and farther from the source of energy.

• Energy can be carried away from its source by a wave. However, the material through which the wave travels does not move with the energy.

•Vibrations set up wave disturbances in a material, and the waves spread away from the source of vibration.

•A vibrating particle passes its energy to a nearby particle. In this way, energy is transmitted through a material.

• Energy Transfer Through a Medium

Most waves transfer energy by the vibration of particles in a medium. A medium is matter through which a wave can travel.

• These are called “mechanical waves.”

• Sound waves, water waves, and seismic waves all need a medium through which to travel.

• Energy Transfer Without a Medium Visible light waves, microwaves, radio waves, and X rays are examples of waves can transfer energy without going through a medium.

• These waves are electromagnetic waves. Although electromagnetic waves do not need a medium, they can go through matter.

TRANSVERSE WAVES• 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.

Crests and Troughs of Transverse Waves

• Transverse waves have alternating high points and low points.

• The high point of a wave is a crest.• The low point of a wave is a trough.

Longitudinal WAVES• 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.

• http://www.acs.psu.edu/drussell/Demos/waves/wavemotion.html

Rarefactions and Compressions of Longitudinal/Compression Waves

• Longitudinal waves do not have crests and troughs.

• The region where the particles of matter are crowded together as the wave of energy moves through is called a compression.

• The region where the particles are spread out as the wave moves through is called a rarefaction.

• http://www.absorblearning.com/media/attachment.action?quick=14w&att=2933

Characteristics of a Wave• Amplitude- the distance the wave oscillates

from its resting position• Wavelength- the distance from crest to crest or

trough to trough• Frequency- Hertz (Hz)- the number of

oscillations in a period of time• Wave Speed- the distance a wave travels in a

given amount of time

SOUND WAVES

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

SURFACE WAVES

• Surface Waves: 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.

SEISMIC WAVES• Seismic waves are caused by earthquakes.• Energy is released when crust breaks.• Seismic waves occur as both transverse and

compressional waves.• Primary waves are compressional and travel

fastest. They can travel through solids and liquids.

• Secondary waves are transverse and travel more slowly due to the way they move. They cannot travel through liquids—like Earth’s liquid outer core.

• Surface waves (Love and Rayleigh) are both transverse and compressional. They move in all directions and cause the most damage.

Hmmmmm . . .

Draw a longitudinal wave and a transverse wave in your composition book. Label the parts of each wave.

Section 2: Wave Properties

Objectives: What you should learn . . .

• Identify and describe four wave properties.

• Explain how frequency and wavelength are related to the speed of a wave.

Amplitude• 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 does.

WAVELENGTH

• 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.

FREQUENCY

• Frequency is the number of waves produced in a given amount of time.

• Frequency can be found by counting the number of crests or troughs that pass a point each second.

• Frequency is usually expressed in hertz (Hz). One hertz equals one wave per second.

• High frequency means more waves per second.• Low frequency means fewer waves per second.• If the amplitudes (wave heights) are equal, high-

frequency waves carry more energy than low-frequency waves.

HERTZ

• A frequency of 1 Hz means that 1 wavelength passes a point in one second. 5 Hz means that 5 waves pass a point in one second.

• As frequency increases, wavelength decreases. In other words, the more waves that go by per second, the distance between them decreases.

How Ocean Waves Workhttp://oceanexplorer.noaa.gov/edu/learning/9_ocean_waves/activities/breaking_waves.html

Deadliest Catch Physics of Waves:http://www.youtube.com/watch?v=edOUDbFtFk0&feature=related

Amplitude of Compressional Waves

• In higher amplitude of a compressional/longitudinal wave, the particles of a compression are closer, and particles in the rarefaction are farther apart.

• In lower amplitude, the particles in compression are farther apart, and rarefaction particles are closer together

More on Compressional Waves

Animation of above compressional wave: http://www.passmyexams.co.uk/GCSE/physics/basic-waves-theory.html

Objectives

• Describe reflection, diffraction, and interference.

• Explain how different media affect wave speed and cause refraction.

• Compare destructive interference with constructive interference.

• Describe resonance, and give examples.

Reflection

• 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.

Law of Reflection• According to the law of reflection, the angle of

incidence is equal to the angle of reflection.• “Incidence” refers to where the wave comes

in contact with a surface.• http://www.teachersdomain.org/asset/lsps07_vid_lightreflect/

Refraction• Refraction is the bending of a

wave as the wave pass from one medium to another at an angle.

• http://www.teachersdomain.org/asset/rr10_vid_refrac/

• 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.

• When light waves travel from air to water, they slow down and bend toward the perpendicular of the surface (normal).

Diffraction

• Diffraction is the bending of waves around a barrier or through an opening.

• The amount of diffraction of a wave depends on its wavelength and the size of the barrier or opening the wave encounters.

Diffraction

• The smaller the wavelength compared to an obstacle the wave encounters, the less it diffracts.

• Sound waves have a larger wavelength than light waves and, therefore, will diffract—or bend around doors and walls easier than light waves.

• That’s why you can hear around corners, but do not see light as easily bend around a corner.

Diffraction of Radio Waves

• Diffraction affects your radio’s reception.

• AM radio waves have longer wavelengths than FM.

• Longer wavelengths diffract (bend) around objects easier.

• Therefore, AM has a tendency to be able to travel farther because obstacles do not get in their way as much.

Interference• Interference is the result of two or more waves

overlapping.• Interference of sounds waves through a

water medium. http://www.youtube.com/watch?v=aWZY3wwldjs&feature=related

Constructive Interference (in-phase)

• 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.

• In other words, the amplitudes (or energy) of the waves add together.

• In sound waves, this increases loudness.

• The result is a new wave that has a larger amplitude than the original waves had.

Destructive Interference (out-of-phase)

• Destructive interference happens when the crests of one wave and the troughs of another wave overlap. The new wave have a smaller amplitude than the original waves had.

• In other words, the waves subtract from one another to create a less energetic wave.

• In sound waves, this causes a reduction in loudness.

• 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 (silence for sound waves).

General Information About Waveshttp://www.bbc.co.uk/schools/gcsebitesize/science/aqa/waves/generalwavesrev1.shtml

The Energy of Waves

Use the terms below to complete the concept map on the next slide.

transversefrequencywaveslongitudinal

wave speedamplitudeenergymedium

Concept Mapping

Chapter 10

The Energy of WavesChapter 10

Concept Mapping, continued

The Energy of WavesChapter 10

Concept Mapping, continued

1. The amount of energy a wave carries depends partly on the wave’s amplitude and wavelength. Which of the following waves has the largest amplitude and the shortest wavelength?

A.

B.

C.

D.

Chapter 10 Standardized Test Preparation

1. The amount of energy a wave carries depends partly on the wave’s amplitude and wavelength. Which of the following waves has the largest amplitude and the shortest wavelength?

A.

B.

C.

D.

Chapter 10 Standardized Test Preparation

2. Ocean waves in deep water often travel in groups of the same wavelength. The image belowshows a group of waves.

Standardized Test Preparation

Explain one way to compare the energy of different waves in the same group.

Chapter 10

2. Explain one way to compare the energy of different waves in the same group.

• Full-credit answers should include the following points:

• The energy carried by a wave is related to its amplitude and its wavelength.

• In a group of waves that have the same wavelength, the amplitude of the waves may vary.

• More energy is needed to move water further away from its resting position.

• Therefore, a wave with a larger amplitude carries more energy than a wave with a smaller amplitude carries.

Standardized Test PreparationChapter 10

3. Some ocean waves are measured as traveling 45 kilometers (km) in one hour. In two minutes, 15 of these waves pass an observer on an island. Calculate the wavelength of these waves in meters (m).

Chapter 10 Standardized Test Preparation

3. Some ocean waves are measured as traveling 45 kilometers (km) in one hour. In two minutes, 15 of these waves pass an observer on an island. Calculate the wavelength of these waves in meters (m).

100 m

Chapter 10 Standardized Test Preparation

4. The diagram below shows the use of a black light. Black lights emit ultraviolet light, which is not visible to humans. After the energy from a black light is absorbed by specially designed inks, the energy is re-emitted by the inks as visible light.

Chapter 10 Standardized Test Preparation

4. continued

Part A. Identify the forms that energy takes as tif flows through this system. Describe each conversion of energy.

Part B. Give two reasons why the energy received by the eye is less than the energy supplied at the electrical outlet.

Chapter 10 Standardized Test Preparation

4. continued

Part A. The energy entering the system is electrical energy. This electrical energy is converted into ultraviolet light and thermal energy by the black-light bulb. The ultraviolet light is converted into visible light energy by the special ink. The visible light is received by the human eye.

Part B. Reason 1: Energy is lost to the surroundings during every energy conversion. For example, electrical energy is lost as thermal energy in the black-light bulb. Reason 2: Only some of the energy emitted by the black-light bulb reaches the special inks because the ultraviolet light energy spreads in all directions away from its source. For the same reason, only some of the visible light energy emitted by the inks reaches a person’s eye.

Chapter 10 Standardized Test Preparation

Chapter 10 Section 1 The Nature of Waves

Chapter 10 Section 1 The Nature of Waves

Chapter 10 Section 1 The Nature of Waves