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Intro to Physics

Intro to Physics. 2 nd semester topics for final exam pt. 2. Waves. Mechanical waves. Non-mechanical waves. Fastest through a vacuum, slowest through solids Can travel through matter or space Ex: electromagnetic waves. Fastest through solids, slowest through gases

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Intro to Physics

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  1. Intro to Physics 2nd semester topics for final exam pt. 2

  2. Waves Mechanical waves Non-mechanical waves Fastest through a vacuum, slowest through solids Can travel through matter or space Ex: electromagnetic waves • Fastest through solids, slowest through gases • Can only travel through matter • Ex: sound, seismic waves

  3. ARE THERE DIFFERENT TYPES OF WAVES? • Mechanical Waves • Non-Mechanical Waves microwaves Sound waves

  4. Electromagnetic Wave http://www.nrc-cnrc.gc.ca/obj/inms-ienm/images/research_images/optical_comb/COMBFIG1.gif

  5. Waves Transverse Longitudinal Vibrations occur in same direction as wave travel Compression-rarefaction structure • Vibrations occur perpendicular to wave travel • Crest, trough structure

  6. TRANSVERSE WAVE crest One wavelength amplitude Rest position trough

  7. LONGITUDINAL WAVE Rarefaction (less dense) Compression (more dense) one wavelength

  8. Wave Characteristics

  9. Wave Characteristics • Frequency (f) (the number of vibrations that occur in a given time) • Hertz (Hz) (# of vibrations per second) • High frequency waves produce waves with short periods and short wavelengths • Period (P) (the time it takes for one wave cycle to pass) • Seconds (s) • The lower the frequency, the longer the period

  10. Wave Characteristics • Wavelength λ (lambda) (the distance between one point on a wave to the next identical point; crest to crest, for example) • Meters (m) • The lower the frequency, the longer the wavelength • Amplitude (longitudinal waves—the tightness of the compression; transverse waves—the distance from the crest to rest position or from trough to rest position) • Meters (m) • The greater the amplitude of the wave, the more energy the wave transfers.

  11. Sound waves

  12. Sound waves and the Ear What is the audible range of frequencies for a human? 20 -20,000 Hz Relative intensity of sound wave is volume and is measured in decibels (dB) What type of wave is a sound wave? Mechanical and Longitudinal The frequency of a sound wave is called pitch. Like all mechanical waves, sound waves can only travel through matter

  13. Seismic waves

  14. Cause • Any physical disturbance that causes the Earth to vibrate • Earthquakes (most commonly) • Volcanoes • Landslides (terrestrial or undersea) • Extraterrestrial impacts (asteroids • and meteorites)

  15. Earthquakes Earthquakes occur when built-up stress is suddenly released. Rupture or slippage of rock within the Earth produce seismic waves http://quake06.stanford.edu/centennial/tour/stop11.html

  16. Earthquakes 2 Earthquake Waves • Earthquake waves travel out in all directions from a point where strain energy is released. This point is the focus. • The point on Earth’s surface directly above the focus is the epicenter.

  17. Body Waves— seismic waves that pass through the Earth 2 • Primary waves, also called P-waves, are longitudinal waves (compressional). • P-waves pass through solids and liquids • P-waves are faster than s-waves. • Secondary waves, also called S-waves are transverse waves. • S-waves can travel through solids but not liquids • S-waves are slower than p-waves

  18. Body Fig. 9-8, p. 194

  19. Fig. 9-10, p. 196

  20. Three types of plate boundaries • Divergent plate boundary 2. Convergent Plate Boundary 3. Transform Plate boundary Fig. 1-14, p. 18

  21. The Mechanism for Plate Motion is Convection in the Mantle Heat from the interior flows outward toward the crust Fig. 1-12, p. 15

  22. P-waves and S-waves provide seismic evidence that the outer core is liquid and the inner core is solid Refraction: the bending of a wave as it passes from one medium to another Caused by changes in wave speed Fig. 9-21, p. 210

  23. Benioff Seismic Zone(associated with a subduction zone at a Convergent Plate Boundary) Pattern of earthquake occurrences indicates the location of the subducted limb of the lithospheric plate

  24. Fig. 2-13, p. 37

  25. Electromagnetic Spectrum Increasing photon energy

  26. WHAT CAUSES Electromagnetic waves (or LIGHT)? Electromagnetic wave (a combination of electric and magnetic fields Vibrating electrically charged particles A changing electric field sets up a changing magnetic field, which sets up a changing electric field, and so on.

  27. HOW DO WE MODEL LIGHT? • TWO MODELS • Wave Model • Particle Model • Physicists recognize the dual nature of light (light travels like a wave, but hits like a particle). • Photon: a massless particle of light (carries energy—greater the frequency, the greater the photon energy)

  28. INTENSITY OF LIGHT Same frequencies of light, just different intensities! An increase in the number of waves or photons (or the amount of light) Brightness of light means intensity. Not related to frequency or the energy per photon! 100 Watts 40 Watts

  29. Photoelectric Effect: the ejection of electrons from certain metals when exposed to certain frequencies of light. Electrons emitted Electromagnetic radiation (visible light range) Photovolatic cell (solar cell) Produces electron flow (electricity)

  30. 29.2The Law of Reflection • Incident rays and reflected rays make equal angles with a line perpendicular to the surface, called the normal. • The angle between the incident ray and the normal is the angle of incidence. • The angle between the reflected ray and the normal is the angle of reflection. • Angle of incidence = Angle of reflection

  31. 29.4Diffuse Reflection • Diffuse reflection allows us to see most things around us. • Light is diffusely reflected from paper in many directions. • Light incident on a smooth mirror is only reflected in one direction. Ordinary paper has a rough surface when viewed with a microscope.

  32. 29.8Refraction of Light As a light wave passes from air into water, its speed decreases.

  33. Refraction • The bending of light as it passes from one medium to another. • Dependent upon • Change in light wave speed • Change in direction • Bending means an abrupt change in direction.

  34. 31.1 Diffraction and Huygens’ Principle The extent to which the water waves bend depends on the size of the opening.

  35. 25.7Interference Interference patterns occur when waves from different sources arrive at the same point—at the same time.

  36. 25.7Interference • In constructive interference, the waves reinforce each other to produce a wave of increased amplitude. Amplitude has doubled in height

  37. 25.7Interference • In constructive interference, the waves reinforce each other to produce a wave of increased amplitude. • In destructive interference, the waves cancel each other and no wave is produced.

  38. INTERFERENCE • The combination of two or more waves that exist in the same place at the same time. • Constructive Interference (additive effect—in phase) • Destructive Interference (subtractive effect—out of phase) • http://www2.biglobe.ne.jp/%7Enorimari/science/JavaEd/e-wave3.html • http://www2.biglobe.ne.jp/%7Enorimari/science/JavaEd/e-wave2.html

  39. Light and colors • Primary colors of light • Red-green-blue

  40. What is color? • When we see color, we are seeing specific frequencies of visible light • VISIBLE LIGHT IS ROYGBIV • Red, orange, yellow, green, blue, indigo and violet • For visible light • Red has the lowest frequency and longest wavelength • Violet has the highest frequency and shortest wavelength

  41. Isaac Newton—discovered that white light is composed of seven different colors of light Red Orange Yellow Green Blue Indigo Violet White Light A prism disperses white light into its primary frequencies of color

  42. 28.2Color by Reflection • This square reflects all the colors illuminating it. In sunlight, it is white. When illuminated with blue light, it is blue. • This square absorbs all the colors illuminating it. In sunlight it is warmer than the white square.

  43. Electricity • More electrons than protons • Negatively charged • More protons than electrons • Positively charged

  44. Voltage • Force that causes charges to move (the push or the electric field) • Voltage exists if there is a potential difference in charges (negatively charged vs. positively charged) • SI unit is Volt (V)

  45. Electric Current • The flow of charged particles. • Charges move from a position of higher to lower electric PE (or higher voltage to lower voltage). • SI unit is ampere (A or amps)

  46. Resistance • Resistance restricts the flow of electric charges. • The cause: internal friction as moving charged particles collide. • Unit for resistance is ohm

  47. Series circuit Parallel circuit http://iss.cet.edu/electricity/pages/a17.xml

  48. Match statements with the correct circuit • Series circuit vs. Parallel circuit • other bulbs go out if one bulb burns out • bulbs maintain same brightness if more bulbs are added • two or more paths for electric current to flow • bulbs dim if more bulbs are added • other bulbs stay lit if one bulb goes out • only one path for electric current to flow 1 2 3 4 5 6

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