1. Light Waves Light is an electromagnetic wave Light travels at a velocity c =  f ( ~ 3x10 8 m/s ) Like sound waves and other waves, light exhibits the same properties seen for other waves. These are diffraction, reflection, refraction and interference. In addition, light waves also exhibit dispersion and polarization.

2. Electromagnetic Spectrum © 2000 Microsoft Clip Gallery

3. Electromagnetic Spectrum Invisible Spectrum Radio Waves Radio Waves Def. – Longest wavelength & lowest frequency. Uses – Radio & T.V. broadcasting.

4. Modulating Radio Waves Modulation - variation of amplitude or frequency when waves are broadcast AM – amplitude modulation AM – amplitude modulation Carries audio for T.V. Broadcasts Carries audio for T.V. Broadcasts Longer wavelength so can bend around hills FM – frequency modulation FM – frequency modulation Carries video for T.V. Broadcasts

5. Short Wavelength Microwave Invisible Spectrum (Cont.) Infrared Rays Infrared Rays Def – Light rays with longer wavelength than red light. Uses: Cooking, Medicine, T.V. remote controls

6. Electromagnetic Spectrum Invisible spectrum (cont.). Ultraviolet rays. Ultraviolet rays. Def. – EM waves with frequencies slightly higher than visible light Uses: food processing & hospitals to kill germs’ cells Helps your body use vitamin D.

7. Electromagnetic Spectrum Invisible Spectrum (Cont.) X-Rays X-Rays Def. - EM waves that are shorter than UV rays. Def. - EM waves that are shorter than UV rays. Uses: Medicine – Bones absorb x-rays; soft tissue does not. Uses: Medicine – Bones absorb x-rays; soft tissue does not. Lead absorbs X-rays. Lead absorbs X-rays.

8. Electromagnetic Spectrum Invisible spectrum (cont.) Gamma rays Gamma rays Def. Highest frequency EM waves; Shortest wavelength. They come from outer space. Uses: cancer treatment.

9. The Visible Spectrum COLORFREQUENCY (Hz)WAVELENGTH (m) R4.0-4.8 x 10 14 750-630 x 10 -9 O4.8-5.1630-590 Y5.1-5.4590-560 G5.4-6.1560-490 B6.1-6.7490-450 V6.7-7.5450-400

10. Color of Light Transparent Objects: Light transmitted because of no scattering Light transmitted because of no scattering Color transmitted is color you see. All other colors are absorbed. Color transmitted is color you see. All other colors are absorbed.Translucent: Light is scattered and transmitted some. Light is scattered and transmitted some.Opaque: Light is either reflected or absorbed. Light is either reflected or absorbed. Color of opaque objects is color it reflects. Color of opaque objects is color it reflects. © 2000 Microsoft Clip Gallery

11. Color of Light (Cont.) Color of Objects White light is the presence of ALL the colors of the visible spectrum. White light is the presence of ALL the colors of the visible spectrum. Black objects absorb ALL the colors and no light is reflected back. Black objects absorb ALL the colors and no light is reflected back.

12. Color of Light (Cont.) Primary Colors of Light Three colors that can be mixed to Three colors that can be mixed to produce any other colored light produce any other colored light Red + blue + green = white light Red + blue + green = white light Complimentary Colors of Light Two complimentary colors combine Two complimentary colors combine to make white light-Magenta,Cyan,Yellow to make white light-Magenta,Cyan,Yellow © 2000 Microsoft Clip Gallery

13. Paint Pigments Pigments absorb the frequency of Pigments absorb the frequency of light that you see Primary pigments Primary pigments Yellow + cyan + magenta = black Primary pigments are compliments of the primary colors of light. © 2000 Microsoft Clip Gallery

14. Complementary Pigments Green, blue, red Complimentary pigments are primary colors for light! © 2000 Microsoft Clip Gallery

15. Diffraction Another property that light exhibits is that it diffracts, which loosely speaking means it bends around the corner when it passes through an opening.

16. Diffraction of Water Waves Diffraction: Waves ability to bend around corners

17. The Principle of Reflection The Angle of Incidence = The Angle of Reflection

18. Reflection

19. Refraction Refraction: The bending of light upon entering a medium with with a different density. A light wave will speed up or slow down in response to a changing medium.

20. Beach Party Imagine lines of people rushing from the parking lot to the sandy beach. People can run faster on pavement than in the sand. Pavement Sand

21. Beach Party Pavement Sand

22. Beach Party Pavement Sand

23. Beach Party Pavement Sand

24. Beach Party As people enter the sand, they slow down. Pavement Sand

25. Beach Party Pavement Sand

26. Beach Party Pavement Sand

27. Refraction Light waves, like people wave fronts, slow down also.

28. Bending Because of Velocity Principle of Refraction: A light wave will slow down upon entering a denser medium. The refracted light will be bent toward the normal to the surface in this case. A light wave will speed up upon entering a less dense medium. The refracted light will be bent away from the normal to the surface in this case.

29. Refraction Velocity slows down and is bent toward the normal to the surface, then speeds up upon exiting the glass and is bent away. Air Glass Surface Normal Incident Angle

30. Dispersion Light of different frequencies is refracted by different amounts Red Light (lower frequency, longer wavelengths) is bent the least. Blue Light (higher frequency, shorter wavelengths) is bent the most. Refraction is Dispersive

31. The Beauty of Dispersion and Refraction Prism Water Drop

32. Index of Refraction To characterize the change in velocity of a light wave in a transparence medium, we use the index of refraction (n). It is the ratio of the speed of light in a vacuum (c) compared to the slower speed of light in a non-vacuum (v). n = c / v Note: since c = 3x10 8 m/s is the speed limit for light, v for any other medium is less than c. Therefore, the index of refraction is always > 1.0

33. Indices of Refraction transparent mediumindex of refraction vacuum 1.0000000 air 1.00029 water 1.33 ice 1.31 salt 1.54 pyrex glass 1.50 quartz 1.46 glycerine 1.47 acrylic 1.70 diamond 2.4

34. Interference The final property of light to discuss is interference, a phenomenon that occurs when two light beams meet. If the two beams enhance each other to give a brighter beam, it is called constructive interference If they beams interfere in a way that makes the total beam less bright, it is called destructive interference.

35. Interference