Unit 6 – Lecture 2

EM Wavesdo not require a mediumwork by vibrating electric & magnetic fields

Electromagnetic Spectrum

The Electromagnetic SpectrumRadio Waves – carry information

radios am fm

televisionsMRIcell phones & cell phone towers

The Electromagnetic SpectrumMicrowaves

microwave ovenDoppler radar

[weather detection]other radar

The Electromagnetic SpectrumInfrared

heat [thermal energy]remote controlsheating lamps for food

The Electromagnetic SpectrumInfrared

picked up by night vision gogglesthermal imagery

some animals can see in infrared [rattlesnakes]

The Electromagnetic SpectrumVisible Light

light bulb…etc.a prism –

separates “white “light into its colors

The Electromagnetic SpectrumUltraviolet UV waves

from sun and other starshelps us make vitamin Dkill bacteria on food [damage cells]fluorescent materials glow [black light]can be seen by some animals [birds, bees]

The Electromagnetic SpectrumX-rays

medical appliationsairport screening

The Electromagnetic SpectrumGamma Rays

radioactive [unit 3!]E emitted

from nucleusmedical applications

radiation therapysterilization

used to look at stars

X-Rays

SoundImportant Sound Terms:

Decibel – unit of sound intensityUltrasonic – above 20,000 hertzEcholocation – using reflected waves

to judge the size, shape, or location of an object

Supersonic – faster than the speed of soundVibration – cause of sound

Soundcaused by vibrationscomposed of compressional waves

in turn this vibrates your ear drum to send signals to your brain

waves must have a medium through which to travel

Sound

Soundspeed of sound is determined by the medium

through which it travelstype of mediumstate of matter

solids, liquids, gasescloser the particles, faster the travel of

soundtemperature of the medium

increased temperature, increased sound this change of speed distorts the sound

The Doppler Effectthe change in pitch and frequency

due to a moving wave source reason why the same thing sounds different

as it approaches you or moves farther awayhigher as approachinglower as moving away

The Doppler Effectbasically…

imagine you’re throwing cheese-balls at someone at regular intervals.[constant frequency]

if you stay in the same place, each ball hits your victim at the same interval [frequency] at which you’re throwing it.

The Doppler Effectbasically…

now, if you start running toward your victim, the distance between you and the person keeps getting smaller

because the distance is smaller, the cheese-ballsare hitting the victim morequickly [with a higherfrequency]

this is why the pitch getshigher as the object approaches.

The Doppler Effectbasically…

…but to you, the frequency is the samethis is how the sound seems to the

person who’s in the car. [it remains the same]

The Doppler Effectbasically…

as you run, you keep throwing the cheese-balls at the same frequency

…but as you get further, it takes moretime for each cheese-ball to reach your victim.

they are being pelted withcheese-balls less often[lower frequency]

this is why the pitch getslower as the object moves farther away

The Doppler EffectIn the story…

what represented the frequency?what represented the sound waves?

What would display the doppler effect moreso:a race car passinga police siren

Speed EquationsSpeed of Sound

speed = distance / time v = d / t

Speed of Wavesspeed = wavelength * frequencyv = λ * f

HomeworkNew worksheet – Speed of Sound ProblemsALSO – work on your packet unless

it’s finishedbecause it’s finished you’re willing to

show it to me and turn it in for collection early.