 # Chapter 7 Section 1: What do you think of when we say waves?

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Chapter 7 Section 1: What do you think of when we say waves?
Waves, Sound and Light

WAVES: Class Wave A wave is a rhythmic disturbance that carries energy without carrying matter, through matter or empty space.

Waves that move through matter: Mechanical
Mechanical Waves Waves that move through matter: Mechanical Mechanical 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 Waves
Transverse 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 Waves
Electromagnetic 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 Wave There are two types of waves. Mechanical and Electromagnetic. Then there are two types of mechanical waves. WAVES Electromagnetic wave Mechanical Waves Compressional Wave Transverse Wave Transverse Wave Transverse wave

A transverse wave has different parts from a compressional wave.

Compressional wave The place where the coils are squeezed together is called a compression. The place where the coils are spread apart are called rarefactions. A series of compressions and rarefactions forms a compressional wave.

Properties of Waves: -Wavelength -Amplitude -Frequency -Speed

Wavelength The wavelength of a transverse wave is the distance between two adjacent crest or two adjacent troughs. The wavelength of a compressional wave is the distance between two adjacent compressions or rarefactions.

Frequency The frequency of a wave is the number of wavelengths that pass by a point each second. The SI unit for frequency is the hertz, (Hz). Frequency = Number of Wavelengths/Time

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

Solving Frequency What 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 wavelengths pass a point in 5s?(use a calculator)

Amplitude The amplitude of a wave is the maximum distance matter moves as the wave passes.

Amplitude of a Transverse Wave
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 Wave
The amplitude of a compressional wave depends on the density of material in compressions and rarefactions. Compressional waves with greater amplitude have compressions that are more squeeze together and rarefactions that are more spread apart.

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

Wave speed Waves are described by their frequency, wavelength and amplitude. Another property of waves is speed. The speed of a wave depends on the material in which the wave travels.

Wave Speed The wavelength, frequency, and speed of a wave are related.
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
Waves don’t always travel in a straight line. Waves can: Reflect (bounce off a surface) Refract (bend) Diffract (bend around an obstacle).

Law of Reflection When 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 Reflection According 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.

Refraction Refraction is the change in direction of a wave when it changes speed as it travels from one material to another. The speed of a wave depend on the what material it travels.

Refraction A light wave travels through air faster than through water.
The picture shows that a change in the wave’s speed changes the direction in which the wave travels. As light changes from air to water it slows down. The change in speed causes the light to bend.

Diffraction Waves can change direction by diffraction.
Diffraction is the bending of waves around and object. The amount of diffraction or bending of the waves depends on the size of the obstacle. In the picture, the obstacle does not completely block the water waves. Instead the waves bend around the obstacle.

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