Waves & Sound

I. Characteristics of Waves Waves Transverse waves Longitudinal waves Measuring waves

A. Waves

Wavesrhythmic disturbances that carry energy through

matter or space

Mediummaterial through which a wave transfers energysolid, liquid, gas, or combinationelectromagnetic waves don’t need a medium

(e.g. visible light)

B. Waves & Energy

Waves Carry energy Waves are caused by

vibrations Can do work Move objects

Energy Waves carry energy Vibration is a transfer

of energy As waves carry

energy the particles in the medium move

the direction of the motion determines the type of wave

C. Categories of Waves

Mechanical Waves Must travel through a

medium Cannot travel through a

vacuum Examples: sound, ocean

waves

Electromagnetic Waves

Does not require a medium Can be transferred through a

vacuum Examples: light, UV rays,

Visible light

D. Types of Waves

Two Types:

Longitudinal Transverse

D. Transverse Waves

Transverse Wavesmedium vibrates

perpendicular to the direction of wave motion

Examples: water waves, electromagnetic waves

B. Transverse Waves

Wave Anatomy

crests

troughs

wavelength

wavelength

amplitude

amplitude

corresponds to the amount of

energy carried by the wave

nodes

E. Longitudinal Waves

Longitudinal Waves (a.k.a. compressional waves)medium moves in the same direction as the wave’s

motionExamples: sound waves, springs, slinky

E. Longitudinal Waves

Wave Anatomy

rarefaction

compression

wavelength

wavelength

Amount of compression corresponds to amount of energy AMPLITUDE

F. Measuring Waves

Frequency ( f )

# of waves passing a point in 1 second

SI unit: Hertz (Hz)shorter wavelength

higher frequency higher energy

1 second

1

Frequency = period ( )

orperiod = the amount of time for one

cycle to do a complete motion

Frequency is measured in hertz (Hz).

1Hz = 1 wave per second

Cyclesecond

F. Measuring Waves

F. Measuring Waves

Velocity ( v )speed of a wave as it moves forwarddepends on wave type and medium

v = × f v: velocity (m/s)

: wavelength (m)

f: frequency (Hz)

F. Measuring WavesSolid

Molecules are close together so waves travel very quickly.

Liquid Molecules are farther apart

but can slide past one another so waves do not travel as fast.

Gas

Molecules are very far apart so a molecule has to travel far before it hits another molecule, so waves travel slowest in gases.

WORK:v = × f

v = (3.2 m)(0.60 Hz)

v = 1.92 m/s

F. Measuring Waves

EX: Find the velocity of a wave in a wave pool if its wavelength is 3.2 m and its frequency is 0.60 Hz.

GIVEN:

v = ?

= 3.2 m

f = 0.60 Hz

v

f

WORK: f = v ÷

f = (5000 m/s) ÷ (417 m)

f = 12 Hz

F. Measuring Waves

EX: An earthquake produces a wave that has a wavelength of 417 m and travels at 5000 m/s. What is its frequency?

GIVEN:

= 417 m

v = 5000 m/s

f = ?

v

f

Ch. 17 – Waves

II. Wave Behavior Reflection Refraction Diffraction Interference Constructive Interference Destructive Interference Doppler effect

A. Wave Interactions

Wave InteractionWhen a wave meets an object or another

wave.When a wave passes into another mediumExamples: reflection, diffraction, refraction,

interference, resonance

A. Reflection

Reflectionwhen a wave

strikes an object and bounces off

incident beam reflected beam

Normal

A. Reflection

When a wave bounces off a surface that is cannot pass through

B. Refraction

Refractionbending of waves when passing

from one medium to anothercaused by a change in speed

• slower (more dense) light bends toward the normal

SLOWER

FASTER

• faster (less dense) light bends away from the normal

B. Refraction

The bending of a wave as it enters a new medium at an angle.

B. Refraction

Refraction depends on…

speed of light in the medium

wavelength of the light - shorter wavelengths (blue)bend more

B. Refraction

Example:

View explanation.

C. Diffraction

The bending of a wave as it moves around an obstacle or passes through a narrow opening.

C. Diffraction

Diffraction

bending of waves around a barrier

longer wavelengths (red) bend more - opposite of refraction

D. Interference

The interaction of two or more waves that combine in a region of overlap

D. Interference

Two types of Interferenceconstructive brighter lightdestructive dimmer light

E/F. Constructive & Destructive Interference

Both are caused by two or more waves interacting, but…

Constructive interference combines the energies of the two waves into a greater amplitude

Destructive interference reduces the energies of the two waves into a smaller amplitude.

G. Doppler Effect

A change in wave frequency caused by movement of sound source, motion of the listener, or both.

Ch. 18 - Waves & Sound

III. The Nature of Sound Speed of Sound Human hearing Doppler effect Seeing with sound

A. Speed of Sound

344 m/s in air at 20°CDepends on:

Type of medium• travels better through solids than through liquids

• can’t travel through a vacuumTemperature of medium

• travels faster at higher temperatures

B. Human Hearing

sound wave

vibrates ear drum

amplified by bones

converted to nerve impulses in cochlea

B. Human Hearing

Pitchhighness or

lowness of a sound

depends on frequency of sound wave

human range: 20 - 20,000 Hz

ultrasonic waves

subsonic waves

B. Human Hearing

Intensityvolume of sounddepends on energy (amplitude) of sound

wavemeasured in decibels (dB)

B. Human Hearing

7080

100110

120

40

1810

0

DECIBEL SCALE

C. Doppler Effect

Doppler Effectchange in wave frequency

caused by a moving wave source

moving toward you - pitch sounds higher

moving away from you - pitch sounds lower

C. Doppler Effect

Stationary source Moving source Supersonic source

same frequency in all directions

waves combine to produce a shock wave

called a sonic boom

higher frequency

lower frequency

D. Seeing with Sound

Ultrasonic waves - above 20,000 Hz

Medical Imaging SONAR“Sound Navigation Ranging”

IV. Electromagnetic Radiation (p.528-535)

EM RadiationEM SpectrumTypes of EM Radiation

A. Electromagnetic Radiation

Electromagnetic Radiationtransverse waves produced by the motion

of electrically charged particlesdoes not require a mediumspeed in a vacuum = 300,000 km/selectric and magnetic components

are perpendicular

The full range of light

B. Electromagnetic Spectrum

B. Electromagnetic (EM) Spectrum

long

low f

low energy

short

high f

high energy

C. Types of EM Radiation

Rabbits Meet In Very Unusual Xciting Gardens

C. Types of EM Radiation

Radio wavesLowest energy EM radiationFM - frequency modulation AM - amplitude modulation

Microwavespenetrate food and vibrate

water & fat molecules to produce thermal energy

C. Types of EM Radiation

Infrared Radiation (IR)slightly lower energy than

visible lightcan raise the thermal energy

of objectsthermogram - image made by

detecting IR radiation

C. Types of EM Radiation

Visible Lightsmall part of

the spectrum we can see

ROY G. BIV - colors in order of increasing energy

R O Y G. B I V

red orange yellow green blue indigo violet

C. Types of EM Radiation

Ultraviolet Radiation (UV)slightly higher energy than visible lightTypes:

• UVA - tanning, wrinkles• UVB - sunburn, cancer• UVC - most harmful,

sterilization

C. Types of EM Radiation

Ultraviolet Radiation (UV)Ozone layer depletion = UV exposure!

C. Types of EM Radiation

X rayshigher energy than UVcan penetrate soft tissue,

but not bones

C. Types of EM Radiation

Gamma rayshighest energy on

the EM spectrumemitted by

radioactive atomsused to kill

cancerous cells Radiation treatment using radioactive cobalt-60.