1. Chapter 14: Light and Reflection

2. 14.1 Objectives Be able to discuss the historical developments and understanding of light. Know the speed of light. Be able to explain how light waves are produced and how they transfer energy. Know the different forms of electromagnetic radiation.

3. What is Light? Greek philosophers discussed the structure of light. Pythagoras: particles Empedocles: waves Euclid: beams

4. Particle or Wave? Isaac Newton—particles Christian Huygens—waves Thomas Young (1801): “proved” waves. Albert Einstein (1905): “proved” particles! Light has wave-like and particle-like characteristics.

5. The Speed of Light Galileo: light is too fast to measure! Olaus Roemer (1676): light from Jupiter takes 16 minutes to cross earth’s orbit. Albert Michelson (1880) c = 3.00 x 10 8 m/s c: celeritas (Latin for swiftness) exactly 299,792,458 m/s

6. Electromagnetic Waves James Maxwell: how fast do EM waves travel?(see it)see it James Maxwell: light is an EM wave! made by vibrating electric charges EM cause electric charges to vibrate, transferring energy require no medium, travel at c c = f

7. Electromagnetic Spectrum

8. 14.2 Objectives (continued) Be able to make calculations related to the intensity of light. Understand the difference between wattage and brightness.

9. Light Intensity light power in lumens (lm) intensity in lux (lx) but same lumens. More watts… Fewer watts…

10. Understand the concept of reflection Understand how curved mirrors form images. Draw ray diagrams. 14.2/14.3 Objectives

11. Reflection reflection: a wave bouncing off a surface law of reflection:  i =  r virtual image: reflect rays diverge; extend to a point behind the mirror

12. real image: rays meet in space; can project on a screen concave mirrors focus or converge light so they can form real images. convex mirrors diverge light rays so they only form virtual images. Curved Mirrors CONCAVECONVEX

13. Ray diagrams can be used to determine… type of image location of image orientation of image size of image Draw ray diagrams for… Object beyond C, concave lens Object inside F, concave lens Object in front of convex lens Ray Diagrams

14. 14.2/14.3 Objectives (continued) Be able to use the Gauss equation as it applies to mirrors. Be able to use the magnification equation as it applies to mirrors.

15. A 7.5 cm tall candle is placed 22.4 cm from a convex mirror with a 15.0 cm focal length. Calculate the image distance, the magnification, and the image height. Describe the image. (+) d i = real(-) d i = virtual (+) f = converge(-) f = diverge (+) h i = upright(-) h i = inverted Mirror Math

16. 14.4 Objectives Understand how our eyes see color through the process of color addition. Understand how pigments absorb colors through the process of color subtraction.

17. Color white light = all colors (Newton) 400 nm — 700nm black = no color Color addition occurs in the eyes/brain. Color is a human perception. Cone cells respond to blue, green, and red light (RGB).

18. Color Addition B + G = C (cyan) G + R = Y (yellow) R + B = M (magenta) B + G + R = W (white)

19. Complementary Colors complementary colors: any two colors that add to make white. red + cyan = white R + (G + B) = white Retinal fatigue flag

20. Color Subtraction pigments absorb certain colors (convert to heat) and reflect others The subtractive primary colors are CYM. C + Y = (W – R – B) = G C = B + G = (W − R) Y = G + R = (W − B) M = R + B = (W − G)

21. CMYK (K is for blacK) Printers also use a black pigment.

22. Objectives Be able to explain why materials are transparent or opaque to various frequencies of EM. Understand why the sky is blue, why the sun is yellow, why sunsets are red, and why the ocean is blue-green. Understand how polarizers work. Understand the concept of a “red shift” or “blue shift.”

23. opaque: dissipative absorption; solid or liquid particles resonate with EM, energy is converted into KE (heat) scattering: gas particles resonate with EM, but EM is emitted in random directions (less converted to KE) transmission (transparent) or reflection: particles don’t (or barely) resonate, EM quickly re- emitted net speed of light in materials < c Light and Resonance

24. Blue Skies and Red Sunsets Rayleigh scattering: violet and blue scattered by N 2 and O 2 The sun appears Y because R and G scatter less. white light At sunset, sunlight travels through more atmosphere; more green scatters, leaving a red sunset.

25. Blue-Green Oceans Water absorbs IR and some red. Water reflects B and G, appearing greenish-blue.

26. Polarization unpolarized light: oriented randomly some surfaces / materials polarize (align) the waves

27. Red Shift (Doppler Effect for Light) Edwin Hubble: the red shift of galaxies increase with distance (expanding universe)