# Waves Chapters 10 & 12.

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Waves Chapters 10 & 12

The Nature of Waves Chapter 10 Sections 1 & 2

What is a wave? Def: a repeating movement that transfers energy through matter Types of waves: Transverse: matter (up/down) moves at right angles with the wave (left/right)

Other Types Compressional: matter moves in the same direction as wave

Parts of a Transverse Wave

Parts of a Compressional Wave

Wave Properties Wavelength: distance between one point on a wave an the next just like it

Wave Properties Frequency: number of wavelengths that pass a fixed point each second Count the # of crests or the # of compressions Unit: Hertz (Hz) = 1/s = s-1 Period: amount of time it takes one wavelength to pass Unit: second

Wavelength vs. Frequency
Long wavelength = low frequency Inversely related: one is up the other is down

Wave Speed Depends on the medium it is traveling through
Sounds: faster in liquids and solids or warmer air Light: slower in liquids and solids

Calculating Wave Speed
speed(m/s)=frequency(Hz)xwavelength(m) c = v 

Calculations A wave has a frequency of Hz and a wavelength of 3.0m. What is the speed of wave? What is the wavelength of a wave that has a frequency of 20.0 Hz and a speed of 340 m/s?

Amplitude and Energy Amplitude: related to the energy carried by the wave High amplitude = High energy

Amplitude and Energy Compressional Amplitude  denser the compressions = higher amplitude

The Behavior of Waves Chapter 10 Section 3

Reflection A wave strikes an object and bounces back
All waves can reflect Echoes – sounds waves reflecting

Law of Reflection Incidence beam and reflected beam
Normal line – perpendicular to mirror Def: angle of i and angle of r are equal

Refraction Light travels at different speeds in different mediums
Change speed – change angle Def: bending of a wave caused by change in speed from one medium to another

Refraction Slower in water – bends towards normal
Faster in air – bends away from normal

Refraction Objects in water are farther than they appear!

Diffraction Def: object causes a wave to change direction and bend around it Diffraction – around an object Refraction – through an object

How much Diffraction? Obstacle smaller than wavelength – waves bend
Obstacle larger than wavelength – waves not affected much Hear sounds from room before see light from room Sound waves close to size of door – bend around door Light – too small doesn’t diffract and bend

AM – longer waves – diffracted much easier – travel farther distances FM – smaller waves – aren’t affected as much – don’t go as far

Interference Def: when two or more waves combine and form a new wave

Constructive Interference
Waves ADD together – crests arrive at same place at same time Amplitude = sum of two

Destructive Interference
Waves SUBTRACT each other – one crest meets with one trough Amplitude – difference of two

Standing Waves Def: wave pattern when waves of same wavelength and amplitude meet from opposite directions Crest/Crest = amplitude Crest/Trough = node Wave “stands still” because it appears to not move - vibrates

Resonance Objects have own natural frequencies
Depends on size, shape, material, etc. Def: object is made to vibrate by absorbing at its natural frequency Object absorbs more energy – higher amplitude – could break apart Tacoma Narrows Bridge

Electromagnetic Spectrum
Chapter 12 Section 2 Electromagnetic Spectrum

What are Electromagnetic (EM) Waves?
Def: vibrating electric charges and can travel through space with no matter

Range of Frequencies EM waves have WIDE range of frequencies
The range = Electromagnetic Spectrum

Radio Waves All around you – can’t see or hear them
Sound = compressional wave Radio = transverse Radio: wavelengths 1 mm or longer

Microwaves – Type of Radio Wave
Def: wavelengths less than 1m Wavelengths of 1cm – 10cm used for cell phones and satellites Microwave ovens? Vibrate water molecules – friction = thermal energy

Send radio wave and measure how long it takes to bounce back – location is found

Magnetic Resonance Imaging (MRI)
Developed in 1980s Cylinder – powerful magnet, radio wave emitter and detector p+ in H atom align to magnet Radio waves cause p+ to flip Flipping releases radiant energy Radio detector reads energy – maps your insides

Infrared Waves Warmth – transmitted by IR waves
Def: wavelengths 1mm – 750 billionths of meter Remotes for TVs – computers reading CD-ROMS Hotter objects – shorter wavelengths – IR imaging

Visible Light ROY G BIV Only form can detect with eyes (rods and cones) Def: wavelengths 750 billionths to 400 billionths of meter Eyes pick up different wavelengths = color Red – long wave Violet – short wave

Ultraviolet Waves Def: wavelengths 400 billionths to 10 billionths of a meter Bad = enter skin cells = wrinkles or cancer UVA – longer waves than UVB (sunburn) Good = allows body to make vitamin D Good = kills bacteria – damage cells = death

Ozone Layer Ozone = O3 Constantly formed and destroyed by UV waves
Destroyed by CFCs – 1 Chlorine atom can destroy thousands of O3

X-rays and Gamma Rays Smallest wavelengths highest frequencies
X-rays: wavelengths of 10 billionths to ten trillionths of a meter Images of bones, bags in airport Gamma Rays: wavelengths shorter than 10 trillionths of a meter Produced in nuclei of atoms X-rays and Gamma Rays used in radiation therapy – kill healthy and diseased cells

Chapter 12 Section 3 Radio Communication

E- produce electric current carries info Amplifier boost current and sends to speakers to vibrate  ears  brain Each station = certain frequency = carrier wave Carrier wave is modified to send info

AM radio AM varies the amplitude of carrier wave – Amplitude Modulation Changing amp – speakers vibrate 540,000 – 1,600,000 Hz Measured in kHz

FM Radio FM varies the frequency of carrier wave – Frequency Modulation Strength is constant = clearer sound 88 mil – 108 mil Measured in MHz

Frequency Usage

Television Radio and TV both use carrier waves
Audio – FM signal Pics – AM signal Pictures formed by cathode-ray tube – sealed vacuumed tube with 1 or more beams of e- produced Color TV – 3 beams of e- directed at screen with magnetic field

Television Screen has over 100,000 rectangular spots that glow red, green or blue when struck Makes image when 3 beams sweep over screen – control color and brightness of each spot

Telephones Sound waves in microphone  electrical signal (radio wave) microwave tower Cell phone uses one signal to send info another signal to receive Each base covers cell – move from cell to cell – automatically transfers signal

Cordless Phones Transceiver – transmits one signal and receives another from a base unit Using dif frequencies allows you to talk and listen at the same time

Satellites Satellite Telephones – can make calls over the world
Phone – satellite – ground station – phone Long delays Satellite TV – high frequency microwaves rather than radio waves Why are dishes curved? To direct waves to antenna

Global Positioning System (GPS)
Def: satellites, ground stations, and receivers give your exact location Satellites owned by US Dept. of Defense – signals used by anyone