Unit 4 notes

Waves & Sound

Characteristics of Waves

 _Waves

Waves

_Waves

_{rhythmic disturbances that carry energy through}

matter or space

_Medium

_{material through which a wave transfers energy} _{solid, liquid, gas, or combination}

_{electromagnetic waves don’t need a medium}

Mechanical Waves

_{Three Types:}

Mechanical Waves

3) Surface Waves Motion is both up-and-down and

Longitudinal Waves

_{Longitudinal Waves (a.k.a. compressional)}

_{medium moves in the same direction as wave}

motion

Motion of wave →

Longitudinal Waves

_{Wave Anatomy}

rarefaction

compression

wavelength

wavelength

Transverse Waves

_{Transverse Waves}

_{medium moves}

perpendicular to the direction of wave motion

Transverse Waves

_{Wave Anatomy}

crests troughswavelength wavelength amplitude amplitude corresponds to the amount of energy carried by

the wave

Measuring Waves

_{Frequency ( f )}

_{# of waves passing}

a point in 1 second

_{Hertz (Hz)}

_Period

_{time required for 1}

wave cycle

1 second

Measuring Waves

Period = 1 Frequency

1 second

_{shorter period} 

shorter wavelength  higher frequency 

higher energy

Measuring Waves

_Recap:

_{Wave anatomy}

_{Wavelength (λ)}

Measuring Waves

Velocity ( v_w )

_{speed of a wave as it moves forward} _{depends on wave type and medium}

v

w

=



×

f

f: frequency (Hz)



WORK:

v_w =  × f

v_w = (3.2 m)(0.60 Hz)

v_w = 1.92 m/s

Measuring Waves

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_w = ?

 = 3.2 m

f = 0.60 Hz



WORK:

f = v_w ÷ 

f = (5000 m/s) ÷ (417 m)

f = 12 Hz

Measuring Waves

 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_w = 5000 m/s

f = ?



Wave Behavior

_{Waves bounce!!}

_{When a wave cannot pass through a surface,}

it will bounce off it

Wave Behavior

_{When waves leave one medium and enter a new} medium, they “turn” because one side slows

Waves & Sound

The Nature of Sound

 _{Speed of Sound}  _{Human hearing}  _{Doppler effect}

Speed of Sound

_{344 m/s in air at 20°C} _{Depends on:}

_{Type of medium}

• travels better through liquids and solids • _{can’t travel through a vacuum}

_{Temperature of medium}

Human Hearing

sound wave

vibrates ear drum

amplified by bones

Human Hearing

_Intensity

_{volume of sound}

_{depends on energy (amplitude) of sound}

wave

Human Hearing

_Frequency

_{human range:}

20 - 20,000 Hz _Pitch

_{highness or}

lowness of a sound

_{depends on}

frequency

ultrasonic waves

Human Hearing

70 80

100 110

120

40

18 10

0

Human Hearing

_Recap!

_{Speed: 344 m/s, but can vary with medium} _{Intensity: another word for amplitude (energy)}

• Loudness: a subjective quality of intensity

_{Frequency: how fast a source vibrates}

Doppler Effect

Doppler Effect

change in wave frequency

caused by a moving wave source

moving toward you - pitch sounds higher

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

Seeing with Sound

_{Ultrasonic waves - above 20,000 Hz}

Medical Imaging SONAR

Ch. 18 - Waves & Light

Electromagnetic Radiation

 _{EM Radiation}  _{EM Spectrum}

EM Radiation

Electromagnetic Radiation

transverse waves produced by the motion of electrically charged particles

does not require a medium

speed in a vacuum = 3.00 x 108 m/s electric and magnetic

EM Radiation

_Photons

_{tiny, particle-like}

bundles of radiation

_{absorbed and released}

by electrons

_{photon energy increases}

EM Spectrum

low f

long 

low energy

high f

short 

Types of EM Radiation

_{Radio waves}

Types of EM Radiation

_{Radio waves}

_{FM - frequency modulation} _{AM - amplitude modulation}

_Microwaves

_{penetrate food and vibrate}

water & fat molecules to produce thermal energy

Types of EM Radiation

_{Infrared Radiation (IR)}

_{slightly lower energy than}

visible light

_{can raise the thermal energy}

of objects

_{thermogram - image made by}

Types of EM Radiation

_{Visible Light}

_{small part of the}

spectrum we can see

ROY G. BIV - colors in order of increasing

Seeing Colors

_{White light}

_{contains all visible colors - ROY G. BIV}

_{In white light, an object…}

_{reflects the color you see} _{absorbs all other colors}

REFLECTS ALL COLORS

Types of EM Radiation

Ultraviolet Radiation (UV)

slightly higher energy than visible light Types:

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

Types of EM Radiation

_{X rays}

_{higher energy than UV}

_{can penetrate soft tissue,}

Types of EM Radiation

Gamma rays

highest energy EM radiation

_{emitted by}

radioactive atoms

_{used to kill}

cancerous cells _{Radiation treatment using}

Light and Matter

_Opaque

_{absorbs or reflects all light}

_Transparent

_{allows light to pass through completely}

_Translucent