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Light (or the ELECTROMAGNETIC SPECTRUM)

Light (or the ELECTROMAGNETIC SPECTRUM). Is light a wave or a stream of particles ?. Light exhibits wavelike and particle like behavior…. It can…. Light exhibits wavelike and particle like behavior…. Why do we say it is a wave? It can: Reflect Refract Diffract Interfere

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Light (or the ELECTROMAGNETIC SPECTRUM)

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  1. Light (or the ELECTROMAGNETIC SPECTRUM)

  2. Is light a wave or a stream of particles?

  3. Light exhibits wavelike and particle like behavior… • It can…..

  4. Light exhibits wavelike and particle like behavior… • Why do we say it is a wave? It can: • Reflect • Refract • Diffract • Interfere • Experience the Doppler Effect

  5. What affects the intensity (brightness) of a light wave? • The wave measurement_______________ determines the intensity (brightness) of light. • What is the mathematical relationship between intensity and…

  6. What is the mathematical relationship between… …the intensity of light (Lux) and the distance (m) from a light source emitting light at a constant rate.

  7. …between Illumination (Lux) and distance (m) from the source? • Illumination is inversely proportional to the distance from the source squared, as shown by I=3.25/d2 • This means if the distance from the source is doubled, the Illumination received is quartered. • For example, Neptune is 30 times farther from the sun than Earth, so the illumination (from the sun) at Neptune is 1/900th what it is at Earth.

  8. Questions about Light, Color and Vision?

  9. Questions about Light, Color and Vision • Why is the sky blue? • Why did those pants look green in the store and brown at home? • Why does his skin look orange? • What is WHITE LIGHT? • What is a Black Light? • How do we see color? • What are the PRIMARY COLORS OF LIGHT? • What are the other colors called? • What are the PRIMARY PIGMENTS (or primary colors of paint)? And, what do pigments do?

  10. Do we see objects because… light comes from them to us… or from us to them ?

  11. Objects can be: • Luminous (emit light) • transparent or translucent (“transmit” light) • Opaque (absorb/reflect light) • To understand these ideas, and how materials can do each of these things, read PCR lesson 2c

  12. What about the sun? • What color is the light from the sun? • Demo

  13. Go Find Out… • What (wave measurement) affects the color of light? • What range of EM waves can humans see? • How many distinct cells do we have to see color? • How do we see other colors? • What are: luminous objects? transparent or translucent objects? opaque objects? • To understand these ideas, and how materials can do each of these things, read PCR lesson 2a-c

  14. “Play” to Learn • Do the PhET simulation Color Vision • Do the RGB bulb version. Test your predictions. • Record any questions that come to mind. Raise your hand when you think one of my demonstrations addresses your question.

  15. The Visible Light Spectrum

  16. DEMO • Three PRIMARY Colors of light: • Three SECONDARY colors of light:

  17. Primary colors of light and COLOR ADDITION • Red • Blue • Green • Red + Blue = • Red + Green = • Blue + Green = • Red + Blue + Green =

  18. Complementary Colors If added in equal intensities… red + _________ = white blue +__________=white ____________+magenta = white

  19. Formative Assessment:WS Color Addition This is not a quiz, but it is administered under quiz conditions, to see what you remember at this time.

  20. HW Find the correct answers to any you got wrong. Then, note the page where the correct answer, or support to get the right answer can be found. Corrected WS is due at the start of class tomorrow.

  21. Pure Pigments Pigments are opaque – they absorb some wavelengths, reflect others. Pure pigments absorb ONLY ONE frequency (band). These should be named for what they absorb or reflect? (Think about what you will see, since you see the light that enters your eyes!)

  22. Primary Pigments& COLOR SUBTRACTION Named for what they REFLECT in white light • Magenta • Yellow • Cyan Pure pigments ONLY absorb ONE color, the color that is opposite them on the color Venn Diagram

  23. Primary Pigments& COLOR SUBTRACTION Named for what they REFLECT in white light • Magenta • Yellow • Cyan In white light, • Magenta + Yellow pigments= • Magenta + Cyan pigments= • Yellow + Cyan pigments= • Magenta + Yellow + Cyan =

  24. Color Subtraction in Opaque and Transparent/Translucent Materials Colored opaque materials (ex: paint) selectively absorb one or more frequencies of light and reflect what is not absorbed. In contrast to opaque materials, translucent materials (ex: tinted filters) selectively absorb one or more frequencies of light and transmit what is not absorbed. It is the pigments that absorb one or more frequencies. What is not absorbed is either reflected or transmitted.

  25. The bulb in the overhead projector ____________________________________________________. The ________________filter on the overhead ____________ ___________ and __________ __________. The ___________ object ___________ the ____________________________, and so looks ___________.

  26. The overhead projector emits white light. This consists of red, blue and green. The filter on the overhead absorbs the blue and green and transmits only red toward the object. The blue object absorbs the red light, and reflects nothing, and so looked black.

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