1. Chapter – 16 Light

2. Electromagnetic radiation – energy carried through space in the form of waves.

3. What is Light? electromagnetic radiation with wavelengths between 400 nm and 700 nm that stimulates the retina of the eye. Nm = 1 x 10 -9 m - 0.000000001 m

4. How fast light travels is dependent of the median in which it travels through. speed of light in a vacuum = 3.0 x 10 8 m/s

5. Visible light is a collection of all the colors of the rainbow which together make white light. Each color has its own wavelength and frequency but they all travel at the same speed (until they hit a medium).

6. Color by addition Primary colors – red, green and blue (together make white) Primary colors can be mixed together to form secondary colors Secondary colors Red and green = yellow Blue and green = cyan Red and blue = magenta

7. Complementary colors Any two colors added together that make white. Ex. yellow is complementary to blue since yellow = green and red then if you add blue you get white. (cyan and red are complementary as is magenta and green)

8. Colors By Subtraction Dye – a molecule that absorbs certain wavelengths of light and transmits or reflects others. Ex. a tomato is red because it reflects red light to our eyes. Pigment – a colored material that absorbs certain colors and transmits or reflects others. Like a dye but can be seen under a microscope, often it is a finely ground inorganic compound.

9. When light hits on a red object the object reflects red back and we see red. If red light is shined on a blue object, which only reflects blue, we will see black because the object absorbed the red light. When you shine a yellow light onto summer grass, what color will you see? green yellow light = red and green, the grass reflects green and absorbs red.

10. Colors in thin film The spectrum you see in soup bubbles or oily water is not the result of a separation of colors or the absorption of colors in a pigment, they are the result of constructive and destructive interference When the film has a thickness of λ/4 the wave reflected back returns to the surface in sync with the first reflected wave. The two reinforce each other as they leave the surface. As the thickness of the film changes, the λ/4 requirement will be met at different locations for different colors. Each color is reinforced where the film is ¼, ¾, 5/4 λ and so on.

11. Polarization of light Polaroid material contains long molecules that allow electromagnetic waves of one direction (those that are parallel to the polarizing axis) while absorbing those vibrating in the other direction (those that are perpendicular to the polarizing axis). Light contains electromagnetic waves vibrating in every direction. On average ½ the waves vibrate in one plane, the other ½ vibrates perpendicular. If polarized material is placed in a beam of light only ½ the light passes through and the intensity of the light is reduced by half. The light is now polarized in one plane of direction. The material used is called a polarizing filter. If a second filter is placed in the light and is perpendicular to the direction of vibration of the polarized light, no light will pass through. Light is also partially polarized by reflection (or even by air) which is why if you rotate polarized lenses the light brightens and dims.