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The Energy of Waves

Preview

Section 1 The Nature of Waves

Section 2 Properties of Waves

Section 3 Wave Interactions

Chapter 20

Concept Mapping



Bellringer

What do you think of when you hear the word wave? Write a brief description of what you think a wave is. Then, write a short paragraph describing a time you might have experienced waves.

Write your responses in your science journal.

Chapter 20



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.

Chapter 20



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. However, the material through which the wave travels does not move with the energy.

Chapter 20


Section 1 The Nature of WavesChapter 20



Wave Energy, continued

• Waves and Work 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.

Chapter 20




• Energy Transfer Through a Medium 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.

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• 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.

Chapter 20



Types of 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.

Chapter 20



Types of Waves, continued

• 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.

Chapter 20


Section 1 The Nature of WavesChapter 20




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

Chapter 20




• 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.

Chapter 20



Bellringer

Draw a longitudinal wave and a transverse wave in your science journal. Label the parts of each wave.

Chapter 20



Objectives

• Identify and describe four wave properties.

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

Chapter 20



Amplitude

• The amplitude of a wave is the maximum distance that the particles of a medium vibrate from their rest position.

Chapter 20

• 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.

Chapter 20



Frequency

• 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.

Chapter 20


Section 2 Properties of WavesChapter 20



Wave Speed

• 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

Chapter 20


Section 2 Properties of WavesChapter 20



Wave Speed, continued

• Frequency and Wavelength Relationship 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.

Chapter 20



Characteristics of a Wave

Chapter 20

Click below to watch the Visual Concept.

Visual Concept



Bellringer

Write the symbols v, f, and in your science journal. Then, write what each symbol stands for, and how each symbol relates to the other two.

Chapter 20



Objectives

• Describe reflection, refraction, diffraction, and interference.

• Compare destructive interference with constructive interference.

• Describe resonance, and give examples.

Chapter 20



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.

Chapter 20



Refraction

• 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.

Chapter 20



Refraction, continued

• Refraction of Different Colors When light waves from the sun pass through a water droplet or a prism, the light is refracted.

• But the different colors in sunlight are refracted by different amounts, so the light is spread out into its separate colors.

Chapter 20



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.

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Interference

• 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.

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

Chapter 20



Interference, continued

• Destructive Interference happens with the crests of one wave and the troughs of another wave overlap. The new wave have 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.

Chapter 20


Section 3 Wave InteractionsChapter 20




• 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.

Chapter 20




• 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.

• An example of resonance is shown on the next slide.

Chapter 20




Chapter 20


The Energy of Waves

Use the terms below to complete the Concept Mapping on the next slide.

Chapter 20

Concept Mapping

transversefrequencywaveslongitudinal

wave speedamplitudeenergymedium


The Energy of WavesChapter 20

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Documents

continued waves

longitudinal waves

water waves

electromagnetic waves

examples of waves

radio waves

seismic waves

experienced waves