Investigating the Behavior of Light part III

1. Investigating the Behavior of Lightpart III SCI 201

2. Unanswered questions What is light anyway? We were pretending it is a ray (like from math class) We know what sound is… but what is light? How does light interact with matter? Why do we see color? Why does light pass through some objects but not others? What is polarization?

3. What is light? If it walks like a duck, sounds like a duck, looks like a duck… it’s probably a duck Light: reflects, refracts, diffracts, interferes, undergoes Doppler Shift, and can be polarized So…?

4. It’s a wave… or thought of as one It is modeled as a wave to explain certain phenomena Transverse (in contrast to sound) If it’s a wave then what’s vibrating? Electromagnetic Waves http://sol.sci.uop.edu/~jfalward/physics17/chapter11/chapter11.html

6. If light is a wave then what is vibrating? Discoveries by Newton and Herschel Different frequencies of vibrating charges produce different “kinds” of Electro-Magnetic (EM) waves Radio waves, microwaves, infrared, visible, ultraviolet, x-rays, gamma rays The electromagnetic spectrum

7. How does light interact with matter? Light bounces off of some materials (reflection) Light can pass through some materials (transmission) Light can also be absorbed by some materials (absorption)

8. Inquiring into colors… Why do some objects appear one color and another object appear another color? What do you remember about mixing paints in elementary school? Look through the different filters at a variety of objects and carefully record your observations. What do you see? Try holding combinations of filters up to the light and carefully record your observations. What do you see? Tape filters onto three flashlights, shine various combinations of light onto a white piece of paper and carefully record your observations. What do you see? How can you explain what you observed?

9. What do we see when we see colors? Usually we see reflected light (opaque objects) selective absorption and resonance - some kind of interaction between the incoming light and the electrons and atoms in the substance Light gets absorbed and re-radiated (#1) Don’t always re-radiate the same frequencies as the incoming light Shirts Why does a yellow shirt look yellow? Why does a yellow cotton t-shirt look different than a blue cotton t-shirt? What are some “sources” of the reflected light?

10. Let’s look at some graphs… White light (#2), Blue filter (#3), Red filter (#4), Yellow filter (#5) Why does a blue object look black through a red filter? (#6) Why do we see green when we look through blue and yellow filters at the same time? (#7) Why don’t the red and blue filters look purple when we look through them at the same time? (#8) So what do filters really do? They subtract some frequencies and re-radiate others…(same thing happens with paint mixing) What about adding colors? (#9, 10)

11. Summary… Color subtraction - produces new colors by removing frequencies Color Addition - produces new colors by adding separate frequencies

12. Blue Skies, Sunsets, Rainbows Blue skies and Sunsets Some molecules are good at absorbing certain frequencies and re-radiating others Diagrams (#11, 12) Sunsets Different frequencies of light are refracted different amounts Diagrams (#13)

13. What is polarization? Try one filter Try two filters Try a third between the first two Explained Corn syrup demo Different frequencies have their directions of polarization rotated different amounts

21. Unanswered questions What is light anyway? We were pretending it is a ray (like from math class) We know what sound is… but what is light? How does light interact with matter? Why do we see color? Why does light pass through some objects but not others? What is polarization?

22. How do we see? The anatomy of the eye Rods and cones Additive primary colors filters