Properties of Light

1. Properties of Light

3. Speed of E.M. Spectrum Waves in a Vacuum • 299,792,458 m/s (3 x 108 m/s), or 186,000 miles per second. • It takes about two and a half seconds, for instance, for a radio communication traveling at the speed of light to get to the moon and back. • Speed decreases as density of medium increases • Change in medium causes refraction (bending) • At this speed it can go around the world 7.5 times in one second c = fλ

5. Electromagnetic Waves • Electromagnetic Waves - energy-carrying waves emitted by vibrating electrons • Light, Radiation, or Photons http://cse.ssl.berkeley.edu/img/em_wave.gif

6. Electromagnetic Spectrum

7. Radio Waves • Longest wavelength, lowest frequency (smallest amount of energy) • Used for radio, television, cellular phones, cordless phones, radio astronomy, microwaves, and RADAR • Types • Shortwave (for very long ranges) • AM (can bend around large objects such as mountains) • FM (strong signals in range of about 50-70 miles) • Television broadcast waves (FM for sound and AM for picture)

8. Infrared Radiation • Heat • Thermograms show how much infrared radiation is being given off by a living thing • Used to view objects in the dark • night vision goggles • Heat lamps use infrared radiation to heat food

9. Visible Light • Only part of the EM spectrum humans can see • 4 x 1014 Hz to 7.9 x 1014 Hz • Visible spectrum of color (from longest wavelength to shortest) • Red (650 nanometers) • Orange • Yellow (580 nanometers) • Green (530 nanometers) • Blue (470 nanometers) • (Indigo) • Violet (400 nanometers)

10. Visible Light • What we call light depends on the overall sensitivity of the eye, ranging in wavelength from 380 nm to 760 nm.

12. Ultraviolet Radiation • Causes us to make vitamin D in our skin • Can be harmful • can cause skin cancer • Used to kill germs and sterilize medical equipment • Nail shops • Safety goggles

13. X rays • Their high energy makes then pass through many materials • Various exposure times allows for numerous views

14. Gamma Rays • Most energetic • Used in radiation therapy to kill cancer cells

15. Important Properties of Light • Amplitude determines brightness • The greater the amplitude, the greater the brightness • Wavelength determines color

16. Light Intensity • Intensity or brightness of the light changes along with the colors http://fuse.pha.jhu.edu/~wpb/spectroscopy/basics.html

17. Inverse Square Law http://www.anees.com/6.html http://www.astrosociety.org/education/publications/tnl/32/starscience2.html

18. Additive Primary Colors of Light • By overlapping or “adding” various colors of light together almost any color can be made. Additive PrimariesRGBRed, Green, and BlueLight

19. Secondary Colors of Light • Colors made by mixing 2 primary colors. • G & R = yellow • R & B= magenta • B & G = cyan http://www.colorado.edu/physics/2000/tv/colortv.html

20. Light Mixing (Additive) • White light is formed where red, blue and green light overlap http://sol.sci.uop.edu/~jfalward/reflection/reflection55.html

21. Photons • Light and EM radiation are composed of small particles called photons. • Photons are thought to be carriers of EM force. • Have either particle or wavelike behavior. This duality in the nature of photons is a key aspect of Quantum theory.

22. Different Wavelengths • Medium dictates speed • Since the photon's energy does not change, its frequency cannot change; therefore its wavelength changes. • Wavelength decreases as the speed decreases.

23. Particle or Wave? • Particles are discrete • energy is concentrated into what appears to be finite space: is homogeneous with definite boundaries • Waves, not considered a finite entity. • Light energy does not exist in a single location, as a wave varies in both place and time. http://www.savagechickens.com/tag/particle

24. Wave Theory Light acts like waves—ripples in space Particle Theory Light acts like particles that stream from the source (creating shadows) Wave Theory VS Particle Theory Photon-massless bundle of concentrated electromagnetic energy http://www.thespectroscopynet.com/Educational/wave_particle_duality.htm

25. Dual Nature of Light

26. Duality of Light Wave-Particle Duality: not strictly one or the other Quantum electrodynamics (QED) combines the wave-particle nature of light into a single theory. Light behaves as a wave When light travels through an opening Light behaves as particles when light bounces off of metal http://nobelprize.org/nobel_prizes/physics/articles/ekspong/index.html http://www.crcs.k12.ny.us/physics/notes/modern/modern_note.htm

27. Photoelectric effect • The photoelectric effect refers to the emission, or ejection, of electrons from the surface of, generally, a metal in response to incident light. • Discovered by Einstein in the early 20th century • electrons are ejected from a solid when impinged upon by electromagnetic radiation • excitation • led to the understanding of light as particles, or photons http://www.physics.uiowa.edu/adventure/fall_2005/oct_15-05.html http://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/energy/nature_of_electromagnetic_radiation_p_2.htm

28. Light as a Particle http://www-inst.eecs.berkeley.edu/~cs39j/sp02/session07.html

29. Polarization • The process of transforming non-polarized light into polarized light is known as polarization. • Polarized light waves are light waves in which the vibrations occur in a single plane. http://www.glenbrook.k12.il.us/gbssci/phys/Class/light/u12l1e.html

30. Light reflected from a horizontal surface is partially polarized in the horizontal plane.

31. http://www.olympusmicro.com/primer/lightandcolor/particleorwave.htmlhttp://www.olympusmicro.com/primer/lightandcolor/particleorwave.html Light consists of transversewaves having components that are perpendicular to the direction of propagation. Polarized Light = wave not particle

32. Polarized Lenses Really Make a Difference! • Light reflected from surfaces like a flat road or smooth water is generally horizontally polarized. • Vertically oriented polarized lenses result in a reduction in glare. • Eliminate reflected glare • Enhance contrast • Great for use during snow or water sports http://www.chicagopearle.com/eyeglasses/lenses/polarized/index.asp http://www.spyoptic.com/img/42:19_tridentPolarized.jpg

33. Are your lenses polarized? http://www.agape1.com/polarized.htm

34. 3-D Glasses • Two projectors project two respective views onto the screen • each with a different polarization. • The glasses are polarized oppositely • allowing only one image into each eye http://www.3dglassesonline.com/how-do-3d-glasses-work/index.html

36. Law of Reflection Angle of incidence is equal to angle of reflection I = incoming light N = Normal R = Reflected light

37. SPECULAR REFLECTION light is reflected in the same forward direction only DIFFUCE REFLECTION light is reflected in many directions Reflected Light

39. Total Internal Reflection • Occurs when light travels from a medium of larger to smaller index of refraction • the light ray can actually bend so much that it never goes beyond the boundary between the two media

40. Total Internal Reflection • If the fish looks upwards it sees the sky, but if it looks at too large an angle to the vertical it sees the bottom of the pond reflected on the surface of the water. • The critical angle to the vertical is equal to the critical angle for total internal reflection at an air-water interface which is approximately 49°.

41. Total Internal Reflection Refracted ray http://www.glenbrook.k12.il.us/gbssci/phys/CLass/refrn/u14l3b.html

42. Fiber Optics Fiber-optic lines are strands of optically pure glass as thin as a human hair The light in a fiber-optic cable travels through the core (hallway) by constantly bouncing from the cladding (mirror-lined walls) total internal reflection

43. Refraction http://fr.wikipedia.org/wiki/R%C3%A9fraction

44. The Law of Refraction • The law of refraction is used to predict the amount of bend, or refraction. • The law of refraction is also known as Snell's Law, named for Willobrord Snell, who discovered the law in 1621.

45. More on Refraction • Assuming that the air on both sides of a window have the same refractive indices • Then the incoming and outgoing light beams are actually parallel

46. Snell’s Law http://www.iop.org/activity/education/Teaching_Resources/Teaching%20Advanced%20Physics/Vibrations%20and%20Waves/Reflection%20and%20refraction/page_4477.html The relationship between the angles of incidence and refraction and the indices of refraction of the two media involved.

47. Bending Towards the Normal ex: light passing from air into water lower to higher density the angle of refraction is smaller than the angle of incidence http://id.mind.net/~zona/mstm/physics/light/rayOptics/refraction/refraction1.html

48. Bending Away From the Normal ex: light passing from water into air higher to lower density the angle of refraction is larger than the angle of incidence. http://id.mind.net/~zona/mstm/physics/light/rayOptics/refraction/refraction1.html

49. Examples of objects that create a Spectrum • Prism • Raindrops • CD’s • Diffraction Grating • The tracks of a compact disc act as a diffraction grating, producing a separation of the colors of white light

50. The color of light emitted by a hot object changes with its temperature. • Glowing object colors: • Reddish coolest glowing object • Orangeish • Yellowish • White • Bluish  hottest glowing object