1. Early Work – Feb. 20 Explain the uses of light Definitions from Ch. 16

2. Test Back

3. Ch 16 Light

4. Light is the range of frequencies of electromagnetic waves that stimulates the retina of the eye

5. Light Wavelength range –400 nm – violet –700 nm – red ROYGBIV Light travels in straight lines –Which makes shadows possible

6. Light Light behaves like both a wave and a particle Use ray model to model the path of light (which thinks of it as a particle)

7. Speed of Light Ole Roemer (1644 – 1710) First to determine light travels at a measurable speed Calculated velocity based on distance and time (Io’s orbit is 42.5 hours) c = 299, 792, 458 m/s c = 3 x 10 8 m/s

8. Practice Problems P 376: 1, 4

9. Early Work – Feb. 22 Explain how Roemer first calculated the speed of light. Turn in vocab and PP 1, 4

10. Sources of Light A luminous body emits light waves –The sun An illuminated body reflects light waves –The moon

11. Luminous Flux Luminous Flux, P –The rate at which visible light is emitted from a source –Measured in lumens, lm –A standard 100-watt light bulb emits 1750 lm

12. Illuminance Illuminance, E –The rate at which light falls on a surface Something we can use more than luminous flux –Measured in lumens per square meter, lm/m 2 Or lux, lx –Since light is emitted radially, use 4 πr 2 to find the surface area of a sphere

13. Illuminance Two ways to increase illumination –Get a brighter source – increase luminous flux –Move object closer Both represented with: 2 4d P E  

14. Luminous Intensity Luminous Intensity – –The luminous flux that falls on 1 square meter of a sphere 1 meter in radius –Measured in candela, cd SI unit for all light intensity  44 2 P d P E 

15. Example What is the illumination on your desktop if it is lighted by a 1750-lm lamp that is 2.50 m above your desk?

16. Practice Problems 6, 7, 9 – 11

17. 16.2 Light and Matter

18. Materials Transparent materials –Light waves are transmitted without distortion Translucent materials –Light waves are transmitted with distortion Opaque materials –Transmit no light, or reflect all light

19. Color Isaac Newton, at 24, did experiments on what he called the spectrum after observing it from a prism Through it unevenness in the glass

20. Color by Addition White light can be formed from the correct combination of red, green, and blue lights Primary Colors – red, green, and blue –Used in TVs Secondary Colors – purple (magenta), cyan, yellow –Red and green  yellow –Red and blue  magenta –Blue and green  cyan

21. Color by Addition If you have a color made by two other colors, then you already have two of the three colors needed to make white light. Complementary Colors – a primary and a secondary that produce white light –Magenta and green –Yellow and blue –Cyan and red

22. Colors by Subtraction Dye – a molecule that absorbs certain wavelengths and transmits or reflects others Pigment – a colored material that absorbs certain colors and transmits or reflects others –Difference is a pigment is larger and can be seen with a microscope –Often pigments are ground inorganic materials

23. Colors by Subtraction Primary Pigment – absorbs one primary color –Yellow – absorbs blue and reflects red and green –Cyan – absorbs red and reflects blue and green –Magenta – absorbs green and reflects blue and red

24. Colors by Subtraction Secondary Pigment – absorbs two primary colors and reflects one –Red – absorbs green and blue –Green – absorbs red and blue –Blue – absorbs red and green

25. Note Primary pigments are secondary lights Primary lights are secondary pigments

26. Mixing Pigments If the primary pigment yellow (which absorbs blue) is mixed with the secondary pigment blue (which absorbs everything but), then you get black because no wavelength is being reflected Remember, when you mix light you get white

27. Bkwk P 389: 2 – 21, 24 – 44 Hmwk due Wed. Feb. 28 Ch. 16 Test – Feb. 28