Chapter 11: WAVES

Section 1-The Nature of Waves

Examples of waves…

A surfer waits for the perfect wave

Microwaves warm up leftover pizza

A CD player brings music (sound waves) to your ears

More examples of waves…

Earthquakes--Energy is transferred in powerful waves that travel through Earth. (Seismic waves)

Light--A type of wave that can travel through empty space to transfer energy from the Sun to the Earth.

Drop a rock into a pool of water The rock has ENERGY

ENERGY is transferred to nearby water molecules

These molecules transfer ENERGY to other molecules

A wave is a repeating disturbance or movement that transfers ENERGY through matter or space.

MECHANICAL WAVES Waves that can travel only

through matter are called

mechanical waves. (Ex. Sound waves require air.)

The matter the waves travel through is called the medium.

The medium can be a solid, a liquid, a gas or a combination of these.

Examples of mediums…

Sound waves = AIR

Ocean waves = WATER

Not all waves need a medium. Light and radio waves travel through space.

There are 2 types of mechanical waves:

1—

TRANSVERSE

Matter in the medium moves back and forth at right angles to the direction that the wave travels.

Examples—ocean wave, rope

2—COMPRESSIONAL

Matter in the medium moves back and forth in the same direction that the wave travels.

Examples—slinky, sound waves

SEISMIC WAVESDuring an earthquake,

Earth’s crust vibrates, creating seismic waves that carry ENERGY outward.

These waves are a combination of TRANSVERSE and COMPRESSIONAL waves.

Compressional—P-wave

Transverse—S-wave

Chapter 11: WAVES

Section 2-Wave Properties

What makes waves different from each other? The medium they travel in

How much energy they carry

How fast they travel

What they look like

What do they look like?

TRANSVERSE WAVES—

Have alternating high points (crests) and low points (troughs).

Compressional waves do not have crests or troughs.

Compressional waves are made of 2 regions:

1. COMPRESSION-coils are close together (dense)

2.RAREFACTION-coils are far apart (less dense)

A wavelength is the distance between a point on a wave and the nearest point just like it.

FREQUENCY

The frequency of a wave is the number of wavelengths that pass a fixed point each second.

Frequency = f

THE ELECTROMAGNETIC SPECTRUM

Frequency Frequency is expressed in

hertz (Hz).

A frequency of 1 Hz means that 1 wavelength passes by in 1 second.

In SI units, 1 Hz is the same as 1λ/s.

This relationship is always true—

as frequency increases, wavelength decreases.

f↑ = λ↓

WAVE SPEED

SPEED = WAVELENGTH X FREQUENCY

v = λ x f

(λ=2m, f=3Hz)

v = 2m x 3Hz (3λ/s)

v = 6m/s

Wave Speed

SPEED = WAVELENGTH X FREQUENCY

v = λ x f

Example: (do on your own)λ = 3 m, f = 10 Hz

Why do some earthquakes cause terrible damage, while others are hardly felt?

Because the amount of energy a wave carries can vary.

AMPLITUDE is related to the ENERGY carried by a wave.

↑ wave’s AMPLITUDE = ↑ wave’s ENERGY

If you’ve ever been knocked over by an ocean wave, you know that the higher the wave, the more energy it carries.

CHAPTER 11: WAVES

Section 3-The Behavior of Waves

REFLECTION-LIGHT WAVESTHE LAW OF REFLECTION—

REGULAR/SMOOTH SURFACESDIFFUSE REFLECTION—ROUGH

SURFACES

REFLECTION—REGULAR OR DIFFUSE?

REFLECTION—ALBEDO VALUES

REFLECTION—SOUND WAVES

REFLECTION—Echolocation—(bats and dolphins)Bat emits sound waves as they

fly.When the sound waves strike an object, the

waves are reflected back the to the bat.

REFLECTION

If you are one of the last people to leave the school building…when you close your locker door, the sound echoes down the empty hall. ECHOES are caused by wave reflection.

REFLECTION occurs when a wave strikes an object and bounces off of it. (Examples--sound, light, water)

ECHO (REFLECTION OF SOUND WAVES)--Sometimes when the sound waves hit another object, they reflect off of it and come back to you. Your ears hear the sound again, a few seconds after you first heard your locker door slam.

SONAR—uses sound waves to find objects that are underwater.

ULTRASOUND—ultrasonic waves are directed into a pregnant women’s uterus to form images of her fetus.

Ultrasonic waves are directed into a pregnant woman’s uterus.

These sound waves form images of her fetus.

CAFETERIA AND STAGE

GYM AND CHORUS ROOM

REFRACTION

Remember that a wave’s speed depends on the medium it is moving through.

When a wave passes from 1 medium to another—such as when a light wave passes from air to water—it changes speed.

REFRACTION is the bending of a wave caused by a change in its speed as it moves through 1 medium to another. (Example—RAINBOWS—LIGHT WAVES PASS FROM AIR TO WATER)

REFRACTION

REFRACTIONTo the observer on the side of the pool, the

swimmer’s feet look closer to the surface than it actually is.

The pencil looks like it is broken at the surface of the water.

DIFFRACTION

DIFFRACTION occurs when an object causes a wave to change direction and bend around it.

DIFFRACTION and REFRACTION both cause waves to bend.

The difference is that refraction occurs when waves pass through an object, while diffraction occurs when waves pass around an object.

ALSO--refraction changes mediums

diffraction stays in the same medium

DIFFRACTION

INTERFERENCE

When 2 or more waves OVERLAP and combine to form a new wave, the process is called INTERFERENCE.

INTERFERENCECONSTRUCTIVE--ADD

DESTRUCTIVE--SUBTRACT

INTERFERENCE