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

• 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

• Transverse waves—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 Transverse waveswaves

• 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

• 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!• 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

• 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 • 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

• 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:

• 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• 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!

Electromagnetic Spectrum

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

• 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)• 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

• 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.• 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

• We know this part of the We know this part of the spectrum by the name : spectrum by the name : LIGHTLIGHT

• RR—red—red

• OO—orange—orange

• YY—yellow—yellow

• GG—green—green

• BB—blue—blue

• II—indigo—indigo

• VV—violet—violet

• ROYGBIVROYGBIV

• Red has the longest Red has the longest λλ, , violet the shortestviolet the shortest

• Light is used in Light is used in photosynthesisphotosynthesis

Ultraviolet Radiation

• Higher freq, shorter λ than 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!

• 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