1. PS 1-7-08 Finish Light Color Uses of Electromagnetic spectrum

2. Properties of Sound How Fast Intensity Pitch Range of sound waves –Infrasound –Ultrasound

3. Use of Sound waves Echolocation Sonar Ultrasound imaging –Sonograms

4. Example of Ultrasonic sound waves 1 to 15 million Hz Passes through most materials, but reflects at medium boundaries Not harmful like x-rays Used more frequently for other purposes

5. Why use ultrasonic waves? Focused into more narrow beams Directed more easily

6. SONAR Sound, Navigation, and RAnging Uses acoustic signals and echo returns to locate objects Ultrasound waves generally used

7. Sonar

8. Homework Pg 498 Problems 1-5 and #9

10. Does light move as particles or waves?

11. Light produces interference patterns like water waves

12. Light can be modeled as a wave Transverse waves Electromagnetic wave (no medium, consist of changing electric and magnetic fields) Reflection, refraction, or diffraction Interference, produce standing waves

13. Wave model can not explain some observations Some frequencies of light can knock off electrons from a metal plate upon impact Some light waves with more energy can not. Dim Blue light does, Bright red does not

14. Light can be modeled as a stream of “particles” These particles are called photons Do not have mass Packets of energy Unlike a wave, located in a particular place Also can be used with reflection, refraction

16. Scientist have not determined if light is only a wave or particle They currently accept either models, depending on the situation

17. Energy and Frequency The energy of light is proportional to frequency Higher frequency  more energy Blue light has more energy than red light

18. Speed of light Depends on medium C = speed of light = 3 x 10 8 m/s in nothing Slows down as the density of material increase Visualized by the bending of light (refraction)

19. Brightness of light measured by objects Luminosity # of photons or wave-fronts passing through a certain area of space Luminosity decreases proportionally with distance

20. Homework on page 498 Question 1: Identify 2 factors that may affect the speed of sound. Answer: type of medium, temperature

21. Homework Question 2: Explain why sound travels faster in water than air Answer: In air, molecules are far apart, collide less often

22. Homework Question #3: Distinguish between infrasound and ultrasound Answer: Infrasound are sound waves with a frequency under 20 Hz. Ultrasound are sound waves greater than 20,000 hz.

23. Homework Question #4: Determine which of the following must change when the pitch gets higher Answer: Frequency increases, wavelength decreases

24. Homework Question #5, Determine which of the following must change when the sound gets louder Answer: a,d Amplitude and intensity increase because there is more energy in the sound wave

25. Homework Question #9: Why are sonograms made with ultrasound waves instead of audible sound waves? Answer: Ultrasound waves pass easily through tissue, audible sound waves do not

26. Quiz question Determine which of the following must change when the pitch gets higher? a) intensity b) wavelength c) speed of the wave d) amplitude e) frequency

27. From Friday Evidence that light travels as a series of waves Evidence that light travels as a stream of particles What is a photon? How does the amount of energy carried by a light wave relate to its frequency?

28. Connections between light and sound Both light and sound can vary in intensity light-brightness sound-loudness Both can vary in speed by change of medium –Light slows down with more dense mediums –Sound speed up with more dense mediums

29. Goals for Today Discuss the electromagnetic spectrum in more detail Determine why you see things as a certain color

30. Electromagnetic Spectrum Visible light make up just a small part of the range of light waves, just like audible sound. Electromagnetic spectrum consists of light at all possible energies, frequencies and wavelengths

32. Similarities between different parts of the spectrum All move at the same speed through a given material All do not need a medium to move All are transverse waves

33. Differences in the spectrum Different waves have different wavelengths and frequencies Different frequencies carry different amount of energy Larger frequency, larger amount of energy

34. Regions of the spectrum Gamma and x-rays have the largest frequency (therefore, smallest wavelength) Small enough to pass through most parts of body without meeting anything In x-rays, those that hit bone are absorbed, and do not hit the photographic plate (dark and light parts)

35. X-ray image

36. The good and bad of gamma and x-rays High energy Interaction may kill living cells or alter them to produce cancerous cells Can also be used to kill cancerous cells a form of “ radiation therapy”

37. Radiation Therapy

38. Ultraviolet light Smaller frequencies than x-rays but more than visible light This is the portion of light spectrum that causes sunburn, even on cloudy days

39. Sunbathers

40. Infrared light Frequencies of light slightly smaller than visible light All matter warmer than absolute zero gives out infrared or “radiant heat” Can be sensed by some living beings Infrared cameras, heat seeking missiles

41. Infrared uses

42. Microwaves and Radio waves Microwave, Radio and TV waves are the largest in wavelength, smallest in frequency Boundary between types is arbitrary

43. Microwaves Microwaves are reflected by metals pass thru air, glass, paper plastic absorbed by fat, water and sugar Energy of wave passes into food, makes molecules vibrate- heat up

44. Uses of microwaves

46. Mobile phones Use microwaves to transmit information Least effected by surroundings

47. Homework Pg 505 Problems 1-5

48. Colors that you see Different wavelengths (and frequencies) correspond to different colors of light An object that reflects a certain wavelength of light has that color If multiple wavelengths of light are reflected, secondary colors are created

49. For light If all visible wavelengths of light are combined in sunlight Humans detect yellow-green the easiest Black is the absence of reflected light Mixing all three primary colors produces white light

50. Certain colors absorbed in water

51. Color of plants on other planets