Chapter: Waves, Sound, and Light

Table of Contents Chapter: Waves, Sound, and Light Section 1: Waves Section 2: Sound Waves Section 3: Light

Waves 1 What are waves? • Different types of waves carry signals to televisions and radios. • Sound and light waves move all around you and enable you to hear and see.

Waves 1 What are waves? • Waves are even responsible for the damage caused by earthquakes.

Waves 1 Waves Carry Energy, not Matter • A wave is a disturbance that moves through matter or space. • Waves carry energy from one place to another. • In water waves, the energy is transferred by water molecules. • When waves travel through solids, liquids, and gases, matter is not carried along with the waves.

Waves 1 2 Types of Waves • Waves usually are produced by something moving back and forth, or vibrating. • It is the energy of the vibrating object that waves carry outward. • Some waves, known as mechanical waves, can travel only through matter. (ex: water waves, earthquake/seismic waves, sound waves, and the waves that travel down a rope or spring) • Waves called electromagnetic waves can travel either through matter or through empty space.

Waves 1 There are 2 types of mechanical waves: Transverse Waves & (longitudinal) compressional waves • A transverse wave causes particles in matter to move back and forth at right angles to the direction in which the wave travels. • High points in the wave are called crests. Low points are called troughs. • The series of crests and troughs forms a transverse wave.

Waves 1 Compressional Waves • Another type of mechanical wave is a compressional wave. • A compressionalwave causes particles in matter to move back and forth along the same direction in which the wave travels.

Waves 1 Compressional Waves • The places where the coils are squeezed together are called compressions • The places where the coils are spread apart are called rarefactions. The series of compressions and rarefactions forms a compressional wave.

Waves 1 Compressional Waves • Seismic waves move through the ground during an earthquake. • Some of these waves are compressional, and others are transverse. • The seismic waves that cause most damage to buildings are a kind of rolling (transverse)waves.

Waves 1 Electromagnetic Waves • Electromagnetic waves are waves that can travel through matter or empty space where matter is not present. (Light, radio waves, microwaves, infrared rays, and X rays are examples of electromagnetic waves.) • Electromagnetic waves are transverse waves. • They contain electric and magnetic parts that vibrate up and down perpendicular to the direction the wave travels.

A ___________ wave is a shaped wave is a shaped wave known for crests and troughs. A transverse wave can be a ___________ wave which travels through matter ONLY or an _____________ wave which can travel through matter OR empty space (a vacuum). Review

Waves 1 Properties of Waves (don’t copy this page) • The properties that waves have depend on the vibrations that produce the waves. • For example, if you move a pencil slowly up and down in a bowl of water, the waves produced by the pencil’s motion will be small and spread apart.

Waves 1 Wavelength • The distance between one point on a wave and the nearest point moving with the same speed and direction is the wavelength. • The wavelength of a transverse wave is the distance between two adjacent crests or two adjacent troughs.

Waves 1 Wavelength • The wavelength of a compressional wave is the distance between two adjacent compressions or rarefactions.

Waves 1 Frequency • The frequencyof a wave is the number of wavelengths that pass by a point each second (or certain amount of time). If you were watching a transverse wave on a rope, the frequency of the wave would be the number of crests or troughs that pass you each second. -The closer the waves are together, the greater the energy carried by the waves.

Waves 1 Amplitude of a Transverse Wave • The amplitude (largeness or height) of a wave is a measure of the distance between a line through the middle of a wave and a crest or trough. • As the distance between crests and troughs increases, the amplitude (largeness or height) of a transverse wave increases.

The greater the force that produces a wave, the greater the amplitude of the wave and the greater the energy carried by the wave. In a transverse wave, the higher the wave, the higher the amplitude. Sounds with greater amplitude will be louder. Light with greater amplitude will be brighter.

Waves 1 Amplitude of a Compressional Wave • The amplitude of a compressional wave depends on the density of material in compressions and rarefactions. • The closer the compressions, the larger the amplitude. • The farther apart the compressions, the smaller the amplitude.

Waves 1 Amplitude and Energy • The vibrations that produce a wave transfer energy to the wave. • The more energy a wave carries, the larger its amplitude. • Seismic waves are produced by vibrations in Earth’s crust that cause earthquakes. • The more energy these waves have, the larger their amplitudes and the more damage they cause as they travel along Earth’s surface.

Waves 1 Wave Speed • The speed of a wave (how fast is travels) depends on the medium in which the wave travels. • You can calculate the speed of a wave if you know its wavelength and frequency using this equation.

Waves 1 Wave Speed • In this equation, v is the symbol for wave speed and f is the symbol for frequency. • The SI unit for frequency is the hertz, abbreviated Hz. One hertz equals one vibration per second, or one wavelength passing a point in one second. • The wavelength is represented by the Greek letter lambda, λ, and is measured in meters.

Waves 1 Waves Can Change Direction • Waves don’t always travel in a straight line. • Waves can change direction when they travel from one material to another. • The waves can reflect (bounce off a surface), refract (change direction), or diffract (bend around an obstacle).

Waves 1 The Law of Reflection • A line that makes an angle of 90 degrees with a surface is called the normal to the surface. • According to law of reflection, the angle that the incoming wave makes with the normal equals the angle that the outgoing wave makes with the normal.

Reflection is the bouncing back of a wave when it meets a surface or boundary that does not absorb the entire wave’s energy. All waves can be reflected. Examples: light reflected off a mirror, echoes (voice, bats, dolphins) Reflection

Waves 1 Refraction • When a light wave moves from air to water, it slows down. • This change in speed causes the light wave to bend. • Refraction is the bending of waves caused by a change in their speed as they pass from one medium to another.

As waves pass at an angle from one medium to another, they may speed up or slow down. The greater the change in speed of the waves, the more the waves will bend. Refraction of light going from air through a convex lens, for example, can make images appear larger as the light waves bend. Refraction

Waves 1 Refraction • Waves can change direction by diffraction,which is the bending of waves around an object. • Prisms or diffraction gratings separate white light into its different components or color by bending the light at different angles depending on the frequencies of the light passing through the prism or diffraction grating. Different colors of light have different frequencies.

Waves 1 Diffraction of Sound and Light • The wavelengths of sound waves are similar to the size of objects around you, but the wavelengths of light waves are much shorter. • As a result, you can hear people talking in a room with an open door even though you can’t see them.

Transmission of waves occurs when waves pass through a given point or medium (matter). Example: Light waves are transmitted through transparent materials that allow most light that strikes them to pass through. Transmission

Only a small amount of light is absorbed when waves are transmitted. Most of the wave passes through the medium (matter). Transmission

Opaque materials allow no light waves to be transmitted through them. Translucent materials transmit some light, but cause it to be scattered so no clear image is seen. Transmission

Absorption of certain frequencies of light occurs when the energy is not transferred through, or reflected by the given medium. Objects or substances that absorb any wavelength of electromagnetic radiation become warmer and convert the absorbed energy to infrared radiation. Absorption

Section Check 1 Question 1 Waves carry _______, not _______. Answer Waves carry energy, not matter. Think of what happens when you shake one end of a rope; a wave travels along the rope, but the rope itself doesn’t move forward.

Section Check 1 Question 1 What is shown at point B in this illustration?

Section Check 1 A. crest B. direction rope moves C. direction wave moves D. trough

Section Check 1 Answer The answer is D. Low points on a wave are called troughs.

Section Check 1 Question 3 The number of wavelengths that pass by each second is the wave’s _______. A. diffraction B. frequency C. rarefaction D. wavelength

Section Check 1 Answer The answer is B. If you were watching a transverse wave on a rope, the frequency of the wave would be the number of crests or troughs that pass you each second.

Sound Waves • Every sound you hear is caused by something vibrating. For example, when you talk, tissues in your throat vibrate in different ways to form sounds. 2 Making Sound Waves • Vibrations transfer energy to nearby air particles, producing sound waves in air.

Sound Waves 2 Sound Waves are Compressional Waves • Sound waves produced by a vibrating object are compressional waves. • A vibrating drum head produces a sound wave. • The drum head produces a compression each time it moves upward and a rarefaction each time it moves downward.

Sound Waves 2 Sound Waves are Compressional Waves • Sound waves can only travel through matter. • The energy carried by a sound wave is transferred by the collisions between the particles in the material the wave is traveling in.

Sound Waves 2 The Speed of Sound • The speed of sound depends on the matter through which it travels. • Sound waves travel faster through solids and liquids.

Sound Waves 2 The Speed of Sound • The speed of sound through a material increases as the temperature of the material increases. • The effect of temperature is greatest in gases.

Sound Waves 2 The Loudness of Sound • What makes a sound loud or soft? • The difference is the amount of energy. • Loud sounds have more energy than soft sounds.

Sound Waves 2 Intensity • The amount of energy that a wave carries past a certain area each second is the intensity of the sound. • This figure shows how the intensity of sound from the cymbals decreases with distance.

Sound Waves 2 Intensity • The intensity of sound waves is related to the amplitude. • Sound with a greater amplitude also has a greater intensity.

Sound Waves 2 The Decibel Scale and Loudness • The intensity of sound waves is measured in units of decibels (dB). • The softest sound a person can hear has an intensity of 0 dB. • Sound with intensities of about 120 dB or higher are painful to people.

Chapter: Waves, Sound, and Light