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2. Very Important Concepts We only “see” what reaches our eyes! We only “see” what reaches our eyes! When light reaches the boundary between two media, some of its energy is reflected, some is transmitted, and some is absorbed. The relative amounts of each depends on… the frequencies of light, the frequencies of light, the angle the light reaches the boundary, the angle the light reaches the boundary, and the nature of the two media. and the nature of the two media.Examples: Light traveling through air reaches colorless glass Light traveling through air reaches colorless glass Light traveling through air reaches colored glass Light traveling through air reaches colored glass Light traveling through air reaches a red sweater Light traveling through air reaches a red sweater

3. Based on these interactions of light with matter, we classify materials as: transparent - readily transmits light; can clearly see objects through them translucent - transmits, but diffuses, light; cannot see objects clearly through them opaque - transmits no light; cannot see through them

4. Visible light is that portion of the electromagnetic spectrum which stimulates the retina of the human eye. Visible spectrum wavelengths range from about 400 nm (violet) to 760 nm (red). Light travels at about 3 x 10 8 m/s through empty space and slightly slower through air. Remember that for all waves, v = f.

5. WHITE light is composed of all colors. Red, orange, yellow, green, blue, violet is the order of increasing frequency or decreasing wavelength. Frequencies directly above this spectrum are ultraviolet. Frequencies directly below this spectrum are infrared.

6. Complimentary colors are two colors that combine to form white light. Red and cyan, green and magenta, blue and yellow blue and yellow are pairs of complimentary colors. Red, green, and blue are called primary colors or secondary pigments. Cyan, magenta, and yellow are called primary pigments or secondary colors.

7. cyanmagentayellow redgreenblue

8. These sites let you simulate mixing colors and pigments of light: link1, link2, link3 link1link2link3link1link2link3 “But I learned that the “But I learned that the primary colors are red, primary colors are red, blue, and yellow – not blue, and yellow – not red, bluegreen.” red, blue, and green.” Read about that and more here. here Activity: Color Mixing

9. The color of an opaque object depends on the colors (frequencies) of light incident upon it and on the colors (frequencies) of light reflected. We only “see” the color(s) that get reflected to our eyes. An object that is “normally” red reflects red light and absorbs any other color that shines on it. This object will appear red if the light that hits it has red in it. It will appear dark, or black, otherwise. When white light (red + green + blue) shines on a red object, the red reflects to our eyes and the green and blue are absorbed. When cyan light (green + blue) shines on a yellow object (reflects red and green), the object will appear green.

10. The color of a transparent object depends on the colors (frequencies) of light incident upon it and on the colors (frequencies) of light transmitted. We only “see” the color(s) that get transmitted to our eyes. A transparent object that is “normally” red transmits red light and absorbs any other color that shines on it. Objects viewed through this transparency will appear red if the light they are giving off has red in it. They will appear dark, or black, otherwise. When white light (red + green + blue) shines on a red transparency, the red passes through to our eyes and the green and blue are absorbed. When cyan light (green + blue) shines on a yellow transparency (transmits red and green), green light is transmitted to our eyes.

11. Now that we know more about color and what colors are seen when light passes through or reflects from various materials, let’s look at how colors are revealed by various natural phenomena.

12. The property of light responsible for the separation of light into colors by a prism is known as refraction. Refraction is defined as the Refraction is defined as the change of direction of a ray of light as it passes obliquely from one medium into another of different transmission speed. View a simulation of refraction through a prism at http://www.geocities.com/capecanaveral/hall/6645/dswmedia/PRISM.HTMhttp://www.geocities.com/capecanaveral/hall/6645/dswmedia/PRISM.HTM. http://www.geocities.com/capecanaveral/hall/6645/dswmedia/PRISM.HTM

13. The properties of light responsible for the separation of light into colors by a rainbow are reflection and refraction. Reflection is defined as the turning back of a wave when it reaches the boundary of the medium through which it is traveling. Learn more about rainbow formation here and here. here

14. Soap Bubbles (and other thin films) The properties of light responsible for the separation of light into colors by a soap bubble (or other thin films) are reflection, refraction, and interference. Interference is defined as the result of the superposition of two or more waves. Explore thin film interference here and here. here

15. Thin Film Interference The color spectrum seen in a soap bubble, or any thin film, results from the interference of the reflections of light from the front and back surfaces of the film. The colors seen depend on the thickness of the film. The light most strongly seen has a wavelength such that the film thickness is an odd multiple of 1/4. Other wavelengths will suffer partial or total destructive interference.

16. What is your mental model of light… reflecting from a surface? transmitting through a material? being absorbed by a material? link

17. Spectroscopes and “Rainbow Glasses” The properties of light responsible for the separation of light into colors by a spectroscope (or diffraction grating) are diffraction and interference. Diffraction is defined as the spreading of a wave around the edge of a barrier or through an opening. View simulations of diffraction here and here. here Activity: Spectroscopes