Light & Electromagnetic Radiation Ch. 19

Electromagnetic Radiation Electromagnetic waves are transverse waves created by the motion of electrically charged particles Electromagnetic waves are transverse waves created by the motion of electrically charged particles Radiation is the transfer of E by electromagnetic waves Radiation is the transfer of E by electromagnetic waves

Electromagnetic Radiation Do not need a medium to transfer E Do not need a medium to transfer E Can travel up to 300,000 km/s (light speed) Can travel up to 300,000 km/s (light speed) Slows down when it passes through matter (s, l, g) but still travels much faster than sound or water waves. Slows down when it passes through matter (s, l, g) but still travels much faster than sound or water waves.

Electromagnetic Radiation In a vacuum: In a vacuum: All EM waves travel at the same speed All EM waves travel at the same speed Frequency and wavelength vary Frequency and wavelength vary Remember: as frequency increases, wavelength decreases Remember: as frequency increases, wavelength decreases

Light Light either passes through, is absorbed by, or bounces off of an object, depending on what it’s made of: Light either passes through, is absorbed by, or bounces off of an object, depending on what it’s made of: Opaque materials Opaque materials Absorb or reflect all light Absorb or reflect all light Cannot see through them Cannot see through them Example: heavy curtains Example: heavy curtains

Light Translucent Materials Translucent Materials Allow some light to pass through Allow some light to pass through Cannot clearly see objects through them Cannot clearly see objects through them Examples: frosted glass, sheer curtains, waxed paper Examples: frosted glass, sheer curtains, waxed paper

Light Transparent Materials Transparent Materials Allow light to pass through Allow light to pass through Clearly see objects through them Clearly see objects through them Example: glass windows Example: glass windows

Light Color Color Why are blue jeans blue? Why are blue jeans blue? Blue jeans absorb all colors except blue. The blue light is reflected back to your eyes. Blue jeans absorb all colors except blue. The blue light is reflected back to your eyes.

Light White White Reflecting all colors – ROYGBV (red, orange, yellow, green, blue, violet) Reflecting all colors – ROYGBV (red, orange, yellow, green, blue, violet) Black Black Absorbs all colors, reflects none back to your eyes Absorbs all colors, reflects none back to your eyes

Light How do you actually see color? How do you actually see color? LightRetina Rods Cones Night vision Absorb color Detailed shapes Photoreceptor Cells

Light Cone cells – 3 types: Cone cells – 3 types: Red, blue, and green (primary colors of light) Red, blue, and green (primary colors of light) Each “measures” the amount of that color of light, and they combine signals to tell your brain the color you’re seeing Each “measures” the amount of that color of light, and they combine signals to tell your brain the color you’re seeing

Color Pigments Pigments Absorb some colors and reflect others Absorb some colors and reflect others Used to create materials that absorb all colors except the one we want Used to create materials that absorb all colors except the one we want Color we want is reflected Color we want is reflected Examples: dye, ink, paint Examples: dye, ink, paint

Color Filters Filters Transparent material that transmits one or more colors of light but absorbs all others Transparent material that transmits one or more colors of light but absorbs all others Color we want is let through Color we want is let through Color of filter is the same as the color it transmits Color of filter is the same as the color it transmits

2 Types of Color Additive Additive Primary colors – R, G, B Primary colors – R, G, B Adding light of different colors to create all colors Adding light of different colors to create all colors Additive because R + G + B = white Additive because R + G + B = white (Colors add to form white, a color that reflects all others) (Colors add to form white, a color that reflects all others)

2 Types of Color Subtractive Subtractive Primary colors yellow, magenta, cyan Primary colors yellow, magenta, cyan Adding pigments so that more color is absorbed and less is reflected Adding pigments so that more color is absorbed and less is reflected Subtractive because Y + M + C = black Subtractive because Y + M + C = black (Colors combine to form black, a color that absorbs all others) (Colors combine to form black, a color that absorbs all others)