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Waves

Waves. Radio waves, x-ray, light, sound, seismic waves (p waves, s waves), waves at the beach!. Definition of wave. 1. A wave is a disturbance that travels through matter (air, water, rock) OR space (no matter) 2. Waves carry or transmit energy. . 2 Kinds of Waves. Mechanical Waves

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Waves

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  1. Waves Radio waves, x-ray, light, sound, seismic waves (p waves, s waves), waves at the beach!

  2. Definition of wave • 1. A wave is a disturbance that travels through matter (air, water, rock) OR space (no matter) • 2. Waves carry or transmit energy.

  3. 2 Kinds of Waves • Mechanical Waves • A mechanical wave travels through a medium. Air, water, earth, are different mediums • Electromagnetic Waves • Electromagnetic waves are produced by the motion of electrically charged particles

  4. Mechanical waves 1. Transverse wave: particles move up and down while the wave moves left or right; particles move perpendicular to the path of the wave. 2. Longitudinal waves (slinky, sound waves) particles move back and forth, or parallel to the path of the wave. 3. Surface waves (beach ball example) combination of transverse and longitudinal. Electromagnetic waves 1. Transverse wave: particles move up and down while the wave moves left or right. Types of Waves

  5. Websites for wave action • http://paws.kettering.edu/~drussell/Demos/waves/wavemotion.html

  6. Parts of a transverse Wave • Crest is the high point of the wave • Trough is the low point of the wave • Amplitude: Height of the wave from the resting point to the crest (+) or height of the wave from the resting point to the trough (-) • Wavelength (symbol λ lambda) The distance from crest to crest or trough to trough.

  7. Frequency • The number of wavelengths in one second Units are 1 = hertz sec • If two waves have the same wavelength but are traveling at different speeds, the wave that is traveling faster will have a higher frequency.

  8. Period • Period: the time it takes for one full cycle (wavelength) of the wave to pass by a given point. • Units are a time like seconds

  9. Period: the time it takes for one full cycle (wavelength) of the wave to pass by a given point. Frequency: the number of wavelengths per second Wavelength: the distance from peak to peak or trough to trough. Speed= wavelength period Frequency= speed wavelength Formulas

  10. Complete wave problems worksheet • Complete quiz

  11. Light is a type of electromagnetic radiation.It can be described in two ways. • Wave model • transverse waves • Particle model of light • Photon: a “particle” of light that has no mass. • A stream of photons make up a “beam of light” • Photons are produced when electrons drop from a high energy level to a low energy level.

  12. The Electromagnetic Spectrum • Definition: The full range of wavelengths of electromagnetic radiation • Visible Light is only one tiny part of the electromagnetic spectrum. • A nanometer is one billionth of a meter or 10-9 meters

  13. Examples of the Electromagnetic Spectrum Diagrams http://www.dnr.sc.gov/ael/personals/pjpb/lecture/spectrum.gif http://www.lcse.umn.edu/specs/labs/images/spectrum.gif http://cassini-huygens.jpl.nasa.gov/mission/images/EM-spectrum.jpg http://www.antonine-education.co.uk/physics_gcse/Unit_1/Topic_5/em_spectrum.jpg

  14. Visible Light • VISIBLE LIGHT: Each different color has its own wavelength • ROY G BIV (red, orange, yellow, green, blue, indigo, violet) • Red light has the longest wavelength • Blues are shorter and violet has the shortest wavelength

  15. Scientific Notation • A method for expressing a large number • Numbers are multiplied by powers of 10 • Example #1 • The speed of light is 300,000,000 m/sec • 300,000,000 m/sec = 3 x 108 m/s • Example #2 • 4,500,000,000,000m = 4.5 x 1012m

  16. Example problem #1 • To use a shortcut for scientific notation, move the decimal point and count the number of places it is moved. To change 18,000 to scientific notation, • move the decimal point four places to the left until you have 1.8 and the number of places that the decimal is moved is the correct power of 10. 18,000 L = 1.8 x 104 L

  17. Example Problem #2 • When a quantity smaller than 1 is converted to scientific notation, the decimal moves to the right and the power of 10 is negative. To express 0.0000021 M in scientific notation. . . • move the decimal point to the right 6 places. 0.0000021 m = 2.1 x 10-6m

  18. Radio Waves (also called: radar, TV, shortwave radio, AM, FM) • Longest wavelength in the electromagnetic spectrum • 1x 10-1 and longermeters wavelength • Used for things like radar systems • Frequency: 3x109 hertz or less • Energy: 2 x 10-24 Joules or less http://tbn0.google.com/images?q=tbn:B7xcX-yQKLCewM:http://bookshelvesofdoom.blogs.com/bookshelves_of_doom/images/2007/08/28/radar22.jpg

  19. Microwaves • Wavelength: 1x 10-3 m to 1x 10-1 m • Used in cooking (microwaves) and communication (cell phones) • Frequency: 3x109 to 3 x 1011 hertz • Energy: less then 2 x 10-24 Joules http://tbn1.google.com/images?q=tbn:qKNdBw42mU5j3M:http://www.telephoneisland.com/Images/Products/Large/DKT2104-CT.JPG

  20. Infrared light (IR) • Wavelength: 7x10-7 to 1x10-3 m • Use: • Infrared light from the sun warms you. • Frequency: 3x1011 to 4 x 1014 hertz • Energy: less then 2 x 10-22 to 3x10-19Joules http://tbn2.google.com/images?q=tbn:PhuKcXZ3aSSqOM:http://z.about.com/d/space/1/5/Y/Q/sun_tour.jpg

  21. Visible Light(also called optical) • Wavelength: 4 x 10-7m to 7 x 10-7 m • The colors that we can see • Frequency: 4x1014 to 7.5 x 1014 hertz • Energy: 10-19 to 5x10-19Joules http://tbn0.google.com/images?q=tbn:-McEQ6OwfLYigM:http://www.alaska-in-pictures.com /data/media/13/rainbow-over-the-muldrow-glacier_1127.jpg

  22. Ultraviolet Light • Wavelength: 1 x 10-8 to 4 x 10-7 m • Use: Some insects can see ultraviolet, causes a sunburn Frequency: 7.5x1014 to 3 x 1016 hertz • Energy: 5 x 10-19 to 2x10-17Joules http://www.crackedanimations.com/portfolio/drawings/sunburn.jpg

  23. X rays • Wavelength: 1 x 10-11 - 1 x 10-8m • Used for x ray imaging • Frequency: 3x1016 to 3 x 1019 hertz • Energy: 2 x 10-17 to 2x10-14Joules http://anatomy.med.umich.edu/radiology/xray/images/wrist_hand_x_ray.gif

  24. Gamma Rays • Shortest Wavelength in the Electromagnetic spectrum • Wavelength 1 x 10-11 m and smaller • Uses: gamma rays are used in “radiation therapy” to kill cancer cells. Emitted from nuclear reactions damages living cells. • Frequency: 3x1019 or greater hertz • Energy: 2 x 10-14 Joules or greater http://gryphonscry.files.wordpress.com/2009/02/radiation-symbol.jpg?w=346&h=463

  25. Spectra from a fluorescent light bulb Different kinds of elements each give off a different spectra. United streaming: Exploring Space: the Universe: “spectroscope” A spectroscope is a tool that will separate visible light into the bands or spectrum of different colors.

  26. Spectra of Stars • By knowing the spectra given off by stars we can tell: • Elements they are made of • Temperature • Pressure • Magnetic field • Can tell If distance between the Earth and the star is increasing or decreasing

  27. 3 TYPES OF SPECTRA http://csep10.phys.utk.edu/astr162/lect/light/spectra.gif

  28. Three main types of spectraType one: continuous spectrum • 1. Continuous unbroken band of colors all wavelength’s or colors of the electromagnetic spectrum. • Made from objects that are • hot solids (like a hot wire in an electric light) • hot liquids (like molten iron) • or compressed gasses deep in a star. http://www.astronomynotes.com/light/rainbow.jpg

  29. Type Two: Bright line or emission spectrum • 2. Bright line or emission spectrum are unevenly spaced series of lines of different colors and brightness. • Made from objects containing elements that are in the form of glowing thin gas or vapor. • Each element has its own unique spectra. • Web site: http://www.colorado.edu/physics/2000/quantumzone/index.html

  30. Example of different bright line spectra from: http://members.misty.com/don/spectra.gif

  31. Type Three: Dark-line spectra or absorption spectrum • 3. Dark Line or absorption spectrum dark lines are where light is absorbed. Shows composition of the stars outer layer or the planet's atmosphere. • Interiors of star’s or planets emit continuous spectrum but some of the radiation is absorbed by that objects atmosphere. This forms the dark lines in a spectrum. • They are in the same place as the bright lines for the same element in a bright line spectra. • http://hea-www.harvard.edu/~efortin/thesis/html/Spectroscopy.shtml

  32. http://csep10.phys.utk.edu/astr162/lect/light/spectra.gif

  33. Doppler effect Police Car Siren: http://www.colorado.edu/physics/2000/applets/doppler2.html http://www.grc.nasa.gov/WWW/K-12/airplane/sndwave.html

  34. Police Car Siren • As the siren approaches you, the waves of sound are squeezed together, and you hear them as being higher-pitched. • After the car passes by, sound waves from the receding siren are stretched apart. You hear these stretched waves as being lower-pitched. Wavelengths from the perspective of the ear not the car.

  35. Stars: cosmic police cars • A star zooming toward you has its light waves squeezed together. You see these light waves as having a higher frequency than normal. The light from an approaching star is shifted toward blue end of the spectrum, or blue-shifted. • A star zooming away from us has light waves stretched out and lower frequency then normal, the light is shifted toward red, red-shifted.

  36. Doppler Effect http://www.cnrt.scsu.edu/%7Edms/cosmology/DopplerEffect/doppler2.gif

  37. The arrows show how the direction a star is moving relative to Earth affects the way we see light. • If shifted toward blue end of spectrum the distance is decreasing. • If shifted toward red end the distance is increasing. • Image: Holt Physical Science p 710, 2008

  38. As the distance between the Earth and a star increase the spectra is shifted toward the red end. http://www.astro.ucla.edu/~wright/redshift.gif

  39. YouTube: Ask an astronomer. • Why is the sky blue • What is red shift?

  40. The same is true with light. As a light wave approaches us its frequency is "shifted" towards the blue part of the spectrum. The frequency is higher with shorter wavelengths. That is, if the light was white to begin with it will now have its wavelength compressed in such a way that it begins appear blue. Likewise, if the light is moving away from us it will appear red because its wavelength is stretched and its frequency is correspondingly lower than before. It is only when the light source is stationary that we can see what color it really is. By looking at the light from stars we can tell if they are coming towards us (Shorter wavelengths (blue shift) or moving away from us (longer wave lengths (red shift).

  41. Hubble found red shifts in the galaxies that he studied and used this information to establish that the universe was expanding and expanding at a rate proportional to its distance. Essentially the greater the distance the faster the expansion rate. • Recessional Velocity = Hubble's constant times distance V = Ho D • Hubbles constant is measured in km/sec/Mpc • Distance is measured in Mpc

  42. Mpc stands for mega parsec. A parsec is a unit of distance in astronomy that uses the apparent shift in position of a distant celestial object star at different times of the year (against background stars) to measure its distance. A star with a shift of 1 arc second would be 1pc from our sun. One parsec is equal to about 3.3 light years. • If you look at the above plot and ask what the past history of the universe you find an interesting thing, all of the galaxies were together at the same place about 15 billion years ago. (The near ones cover their short distance at a slow speed, the far ones cover a longer distance at higher speed.) It is a little more complicated than that, the gravitational attraction of everything in the universe on everything else has been slowing down the expansion, so that in the past galaxies were moving away from each other more quickly. This means that the universe is younger. The best estimate for the age of the universe in 2001 is 14 billion plus or minus 2 billion years. (Where a billion is 109 years in standard American usage)

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