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CH 10, 11 & 12. Waves. The Nature of Waves. Rhythmic disturbances that carry E through matter or space Water waves transfer E through water Earthquakes transfer E with shock waves through the Earth Water and the Earth are the MEDIUM —material through which the waves transfers E

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the nature of waves
The Nature of Waves
  • Rhythmic disturbances that carry E through matter or space
  • Water waves transfer E through water
  • Earthquakes transfer E with shock waves through the Earth
  • Water and the Earth are the MEDIUM—material through which the waves transfers E
  • Medium can be liquid, solid, gas or combination of these
  • Some waves do not need a medium; radio and light waves can travel through the emptiness of space
types of waves
Types of waves
  • Transversewaves—the medium moves at right angles to the direction the wave travels
  • In a water wave the water moves up and down, while the wave moves horizontally
  • Compression waves—the matter vibrates in the same direction as the wave travels
  • Sound waves are compression waves—they need a medium to travel---that is why you cannot hear sound in space
transverse waves
Transverse waves
  • Crest are the highest points
  • Troughs are the lowest
  • Wavelength (λ) is the distance between 2 identical points on adjacent waves—doesn’t have to be crest to crest or trough to trough
  • Amplitude is the distance from the rest position of the medium to the crest or trough
  • Larger amplitude—larger amount of E
  • Tsunamis carry ENORMOUS amounts of E
slide5
Frequency (f) is the number of crests that pass a certain place each second
  • Measured in Hertz (Hz) waves per second
  • As frequency goes up the wavelength becomes shorter (closer together)
  • Wave velocity= λ x f
  • m/s = m x Hz
  • A wave in a wave pool has a frequency of .60 Hz and a wavelength of 3.2 m. Calculate its velocity.
whiteboards
Whiteboards!
  • You have a long rope and you are making waves by shaking it up and down. What is the wave’s velocity if the wavelength is 1.2 m and the frequency is 4.5 Hz?
  • A tsunami wave is 13.0 m in length, and has a frequency of 200.0 Hz. Calculate the speed of the wave.
  • Another wave is traveling at 25.6 m/s with a wavelength of .2 m. Calculate its frequency.
  • Yet another wave is traveling at 122.0 m/s with a frequency of 56.0 Hz. What is the wave’s wavelenth?
compression waves
Compression waves
  • The area that is close together is the compression
  • Less dense area is the rarefaction
  • The matter does not move with the wave—only the E moves forward
  • EX Every time you hear a sound, you don’t feel a puff of air along with it
  • Wavelength (λ) = 1 compression and 1 rarefaction
  • Frequency is the # of compressions that pass a place each second
  • Amplitude is the amount of the compress—depends on the E of the wave—more E, tighter compression
sound waves
Sound waves
  • When you speak your vocal cords produce compression waves that travel through the air causing compressions and rarefactions among the particles in the air
  • Speed of sound waves depends on the medium and its Temp
  • Air is the most common, but liquids and solids are better—WHY?
  • Sound travels faster at warmer Temps—WHY? 20°C: 344m/s and at 0°C: 332m/s

Humid better than dry conditions—WHY?

seismic waves
Seismic Waves
  • Carry E outward like a pebble hitting the water—move out from the focus in all directions
  • Epicenter is point on the Earth’s surface directly above the focus
  • They can travel through the Earth and on the surface
  • Seismic waves from the same earthquake are recorded all over the world using a seismograph
  • Richter scale is a numerical description of the size of a seismic wave; an increase of 1 on the scale represents a 10x increase in the size of the waves
  • EX a tremor of 2 on the scale has 10x larger waves than a 1; a 3 has 100x bigger waves than a 1
earthquakes produce 3 types of waves
Earthquakes produce 3 types of waves:
  • Primary waves (p)– cause matter to stretch and compress –they are the fastest
  • Secondary waves (s)—slower and they move matter from side to side like horizontal transverse waves
  • Surface waves—seismic waves that cause a rolling motion in the rock and soil, like vertical transverse waves
faults
Faults
  • Strength of an earthquake depends on how much E has built up along the fault
  • 3 types: Normal: rocks above fault line move down
  • Reverse: rocks move up and over the rocks on the other side—mts are formed this way
  • Strike-slip: rocks on both sides of the fault slide past each other—San Andreas fault is this type—parts of CA are moving north to Alaska!
em waves
EM waves
  • Transverse waves produced by the motion of electrically charged particles
  • They do not require a medium to transfer E
  • They travel through empty space (vacuum) at 300,000 km/s or 300,000,000m/s!
  • Travel slower through any type of matter but still much faster than sound waves
slide14
All EM waves travel at the same speed in each medium, but their frequencies and λ differ
  • The shorter the λ, the higher the frequency
  • Classified from low freq (long λ) radio waves to high freq (short λ) gamma rays
  • Draw the EM spectrum in your notes from pg 360 if you don’t have these notes
particle theory 1905
Particle Theory (1905)
  • Radiation not only carries E but also has momentum which is particle-like behavior
  • Einstein said that light is composed of tiny mass-less bundles of radiation called photons
  • Photons with high E can damage matter, including us!
types of em waves
Types of EM Waves
  • Radio waves: low freq, very long λ, low photon E
  • Also used in TV, cell phones, cordless phones: sound is turned into transverse waves (electric currents) that represent voice patterns and pitch
  • Microwaves have the highest freq of all radio waves
  • Used in communications and cooking
  • They pass right through paper, plastic and glass w/o heating them (food heats up causing the container to heat up)
em waves cont
EM waves cont.
  • Infrared Radiation (IR) is heat; most from the sun, but warm objects give off more IR than cooler objects
  • Dr’s can measure the amount of IR given off as a diagnostic tool: tumors give off more heat than surrounding tissue; called thermograms
  • Also used in military for night vision and heat seeking missiles
visible radiation
Visible Radiation
  • We know this part of the spectrum by the name : LIGHT
  • R—red
  • O—orange
  • Y—yellow
  • G—green
  • B—blue
  • I—indigo
  • V—violet
  • ROYGBIV
  • Red has the longest λ, violet the shortest
  • Light is used in photosynthesis
ultraviolet radiation
Ultraviolet Radiation
  • Higher freq, shorter λthan visible light
  • Higher photon E with more penetrating power
  • UV is necessary for vitamin D production in skin cells BUT prolonged and frequent exposure leads to skin cancer
  • Ozone (O3) layer protects us, but continued use of CFC’s is destroying this layer (go to pg 364 and draw the diagram in your notes)
deadliest rays
Deadliest Rays!
  • X-Rays were discovered by German physicist Wilhem Roentgen in 1895
  • He couldn’t explain the mysterious rays so he called them “x-rays”
  • They are absorbed by dense material (bone) but pass through skin and muscles
  • Gamma rays have the highest freq and the shortest λ, making them the most penetrating of all EM waves—can penetrate through several cm of lead!
  • Used to kill cancer cells/tumors