Download - Unit 6 – Lecture 2. EM Waves do not require a medium work by vibrating electric & magnetic fields
The Electromagnetic SpectrumRadio Waves – carry information
radios am fm
televisionsMRIcell phones & cell phone towers
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 SpectrumGamma Rays
radioactive [unit 3!]E emitted
from nucleusmedical applications
radiation therapysterilization
used to look at stars
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
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