Chapter 7

Section 1: What do you think of when we say waves?

Waves, Sound and Light

WAVES: Class WaveA wave is a rhythmic disturbance

that carries energy without carrying matter, through matter or empty space.

Mechanical WavesWaves that move through matter:

MechanicalMechanical waves move through matter: air, water, dirt, and other objects.Ex: Water! Energy is transferred from

molecule to molecule they are transported without the molecules moving themselves

- The matter that it travels through is called a Medium

- Mechanical waves are produced by something vibrating

Ex: Rope

Types of Mechanical WavesTransverse

◦ Wave energy causes matter in the medium to move up down or back and forth at right angles

◦ Rope◦ Peaks: Crests◦ Valleys: Trough

Compressional◦ Longitudinal

Waves◦ Matter moves

forward and backward in the same direction

◦ Slink

Electromagnetic WavesElectromagnetic waves move through empty space and matter: air, water, dirt, and other objects

plus they can travel through space

- Ex. Sun rays, radio waves, infrared, X rays

- Transverse

Types of WaveThere are two types of waves.

Mechanical and Electromagnetic. Then there are two types of

mechanical waves.

Mechanical Waves

Electromagnetic wave

WAVES

Transverse Wave

Compressional

WaveTransverse WaveTransverse

wave

Transverse waveA transverse wave has different parts

from a compressional wave.

Compressional waveo The place where the coils are

squeezed together is called a compression.

o The place where the coils are spread apart are called rarefactions.

o A series of compressions and rarefactions forms a compressional wave.

Properties of WavesProperties of Waves:

-Wavelength-Amplitude-Frequency

-Speed

Wavelengtho The wavelength of a

transverse wave is the distance between two adjacent crest or two adjacent troughs.

o The wavelength of a compressional wave is the distance between two adjacent compressions or rarefactions.

Frequencyo The frequency of a wave is the

number of wavelengths that pass by a point each second.

o The SI unit for frequency is the hertz, (Hz).

Frequency = Number of Wavelengths/Time

Frequency: how many wavelengths pass a point at a given timeNote: as Frequency increases wavelength decreases

Solving FrequencyWhat is the frequency of a wave if 10

wavelengths pass a point in 2 s?

What is the frequency of a wave if 50 wavelengths pass a point in 5 s?

What is the frequency of a wave if 100 wavelengths pass a point in 10s?

What is the frequency of a wave if 482.5 wavelengths pass a point in 5s?(use a calculator)

Amplitudeo The amplitude of a wave is the

maximum distance matter moves as the wave passes.

Amplitude of a Transverse Waveo For a transverse wave, the

amplitude is the distance from the top of a crest or the bottom of a trough to the rest position of the material.

Amplitude of a Compressional Waveo The amplitude of a

compressional wave depends on the density of material in compressions and rarefactions.

o Compressional waves with greater amplitude have compressions that are more squeeze together and rarefactions that are more spread apart.

Amplitude and EnergyThe larger the amplitude of a wave, the more energy the wave carries.

Wave speedo Waves are described by their

frequency, wavelength and amplitude.

o Another property of waves is speed.

o The speed of a wave depends on the material in which the wave travels.

Wave Speedo The wavelength, frequency, and

speed of a wave are related.o To calculate the speed of a wave

the following formula is needed:

Wavelength(in m) = Wave speed (in m/s)

Frequency (in Hz

Waves can Change Direction

o Waves don’t always travel in a straight line.

o Waves can:o Reflect (bounce off a surface) oRefract (bend)o Diffract (bend around an obstacle).

Law of ReflectionWhen waves reflect off a surface, they always obey the law of reflection. A line that makes an angle of 90 degrees with a surface is called the normal to the surface.

The Law of ReflectionAccording to the Law of Reflection,

the angle that the incoming wave makes with the normal equals the angle that the outgoing wave makes with the normal.

Refractiono Refraction is the change in direction of

a wave when it changes speed as it travels from one material to another.

o The speed of a wave depend on the what material it travels.

Refractiono A light wave travels through air faster

than through water. o The picture shows that a change in the

wave’s speed changes the direction in which the wave travels.

o As light changes from air to water it slows down.o The change in speed causes the light to bend.

Diffractiono Waves can change direction by diffraction.o Diffraction is the bending of waves around

and object.o The amount of diffraction or bending of

the waves depends on the size of the obstacle.

o In the picture, theobstacle does not completely block the water waves. Instead the waves bendaround the obstacle.