Light & Sound

1. Light & Sound

2. Electromagnetic Radiation • Energy that has properties of both particles and waves • Particles – have mass and occupy space • Waves – no mass but carry energy

3. Electromagnetic Radiation – www.google.images http://www.ndt-ed.org/EducationResources/CommunityCollege/RadiationSafety/theory/nature.htm

4. Wave properties • Amplitude – the height of the waves

5. Wave properties • Frequency () – the number of waves that pass a given point per unit of time units of hertz (Hz or s–1) Low High

6. Wave properties • Wavelength () – the distance between a crest and a crest or a trough and a trough in m or nm

7. Relationship of frequency and wavelength Frequency x wavelength = speed  = c (speed of light) c = 2.998 x 108 m/s

8. 1. Lasers used with DVD players have a wavelength of 650 nm. What is the frequency of this light in hertz (Hz)?

9. 2. Calculate the frequency of yellow light that has a wavelength of 584 nm. 3. Calculate the wavelength in nm of violet light having a frequency of 7.32 x 1014 Hz.

10. Electromagnetic Radiation Figure 7.10 General Chemistry, 4th Ed., Hill, Petrucci, McCreary and Perry

11. Electromagnetic Radiation Fig 3.3

12. l ~ 650 nm • ~ 575 nm l ~ 500 nm l ~ 480 nm l ~ 450 nm Fig 7.11 General Chemistry, 4th Ed., Hill, Petrucci, McCreary and Perry Continuous Spectra White light passed through a prism produces a spectrum – colors in continuous form. The different colors of light correspond to different wavelengths and frequencies

13. Fig 7.12 General Chemistry, 4th Ed., Hill, Petrucci, McCreary and Perry Line Spectra

14. Line Spectra The pattern of lines emitted by excited atoms of an element is unique = atomic emissionspectrum Fig 7.13 General Chemistry, 4th Ed., Hill, Petrucci, McCreary and Perry

15. ΔElevel= h Fig 7.17 General Chemistry, 4th Ed., Hill, Petrucci, McCreary and Perry

16. Demonstration with light items

17. 1905 Albert Einstein – photons  energy packets explained the photoelectric effect E = h h = 6.626 x 10–34 joules (J) Planck’s constant

18. Fig 7.15 General Chemistry, 4th Ed., Hill, Petrucci, McCreary and Perry

19. Sound moves in waves through a medium (air) having a random arrangement of molecules in a constant rate that is recognized by the ear http://arts.ucsc.edu/EMS/music/tech_background/TE-01/teces_01.html

20. If sound hits a soft surface, the wave moves around the object, but if it hits a rigid surface, 1. a wave is set up within the material and is a function of the composition of the material 2. rest of the energy is reflected in waves like light off a mirror as a function of distance http://arts.ucsc.edu/EMS/music/tech_background/TE-01/teces_01.html

21. If sound hits a surface with a small hole, the wave moves through the hole in waves, If 2 or more holes are present, diffraction occurs http://arts.ucsc.edu/EMS/music/tech_background/TE-01/teces_01.html

22. diffraction  when waves add (reinforce or constructive interference) or subtract (nulls or destructive interference) http://arts.ucsc.edu/EMS/music/tech_background/TE-01/teces_01.html

23. constructive interference – sound gets louder destructive interference – sound gets softer Sound effects easily observed by the ear http://www.mrfizzix.com/instruments/basics.html

24. Energy Intensity = Time x Area Power Intensity = Area OR http://www.mrfizzix.com/instruments/basics.html

25. Sound Ranges Humans can hear sounds between 20Hz-  20000Hz Ultrasonic waves are waves above 20000Hz; Infrasonic waves are waves below 20Hz Most bat and dog communication is ultrasonic while elephants and whales are infrasonic www.physics.ubc.ca/~outreach/phys420/p420_03/.../overheads.doc

26. Pitch How the brain interprets the frequency of an emitted sound. higher the frequency, the higher the pitch. lower the frequency, the lower the pitch Frequency is in 1 Hertz = 1 vibration/sec www.physics.ubc.ca/~outreach/phys420/p420_03/.../overheads.doc

27. tonie3c.blogspot.com

28. www.healthinformation.nhs.uk

29. scienceblogs.com

30. Demonstration with tuning forks • Smaller forks have higher pitch • Larger forks have lower pitch

31. Demonstration with Physics of Music • Experiencing pitch

32. Doppler Effect • Christian Doppler (1805-1853): An Austrian physicist who conducted experiments with musicians on railway trains playing instruments as the train approached them and receded from them. www.physics.ubc.ca/~outreach/phys420/p420_03/.../overheads.doc

33. Doppler Effect The Doppler Effect is a change in pitch, due to the relative motion between a source of sound and the receiver. common example: change in pitch as a car horn or siren on a vehicle moves past us www.physics.ubc.ca/~outreach/phys420/p420_03/.../overheads.doc

34. Doppler Effect Illustrated www.physics.ubc.ca/~outreach/phys420/p420_03/.../overheads.doc

35. http://boomeria.org/physicslectures/secondsemester/light/astronomy/doppler.jpghttp://boomeria.org/physicslectures/secondsemester/light/astronomy/doppler.jpg

36. http://cse.ssl.berkeley.edu/bmendez/ay10/2002/notes/pics/bt2lf0615_a.jpghttp://cse.ssl.berkeley.edu/bmendez/ay10/2002/notes/pics/bt2lf0615_a.jpg

37. Doppler Effect Applications Radar Gun • Measure the speed at which a pitcher throws • Catch speeder • Track the motion of precipitation caused by storm clouds • Ultrasound • Measure the rate of blood flow in the arteries or the heart. • Light • “Red-shift”-calculate galaxy speeds • As other galaxies move away from us, the light has a lower frequency than if it were at rest. www.physics.ubc.ca/~outreach/phys420/p420_03/.../overheads.doc

38. http://mmlweb.rutgers.edu/music127/midi/basic_sound.htm