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CH 10, 11 & 12

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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CH 10, 11 & 12

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  1. CH 10, 11 & 12 Waves

  2. 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

  3. 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

  4. 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

  5. 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.

  6. 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?

  7. 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

  8. 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?

  9. 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

  10. 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

  11. 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!

  12. Electromagnetic Spectrum

  13. 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

  14. 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

  15. 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!

  16. 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)

  17. 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

  18. 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

  19. 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)

  20. 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

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