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LIGHT Wave - Particle Duality of Light some experiments indicate that light behaves like a wave and others indicate that it behaves like a stream of particles. No one has actually seen light waves - it is just a model to explain the behavior of light. Light is a source of energy. A source of light must produce or transform energy. Light is the range of frequencies of electromagnetic waves that stimulates the retina of the eye. Light is transmitted in straight lines. Light from a source, such as the sun or a bare light bulb, generally spreads out in all directions, in straight lines. Light given off by a bulb can be concentrated into a beam by a flashlight or spotlight. Speed of light = 2.997996 x 10 8 m/s Transparent object - where most of the light passes through; objects can be seen clearly through transparent objects. Ex. Clear glass and plastic. Translucent object - the light is scattered; you cannot see things clearly. Ex. Frosted glass. Opaque objects - you cannot see through opaque objects; the light is absorbed or reflected by these materials. Ex. Wood, brick, soil. COLOR One of the mot beautiful phenomena in nature is a rainbow. Artificial rainbows can be produced by prisms. In 1666, Newton did his first scientific experiments on the colors produced when a narrow beam of sunlight passed through a prism. Newton called the ordered arrangement of colors from violet to red a SPECTRUM. Newton thought there was unevenness in the glass might be producing the spectrum. To test this assumption, he allowed the spectrum from one prism to fall on a second, reversed prism. If the spectrum were caused by irregularities in the glass, the second prism should increase the spread in colors. Instead, a spot of white light was formed. White light is composed of colors. Colors of the spectrum are associated with specific light wavelengths. The color of the light is related to the wavelength or frequency of the light (that to which our eyes are sensitive). Wavelengths of light waves have a range of about 400 nm to 750 nm. R O Y G B V 7x10-7 4x10-7 m Why do we see colors? • many materials contain chemical substances called dyes or pigments that absorb only certain wavelengths of light and reflect others. • dye: molecule that absorbs certain wavelengths of light and transmit or reflect others. • pigment: colored material that absorbs certain colors and transmits or reflects others. Primary Colors White light can be formed from colored light in a number of ways. • if correct intensities of red, blue, and green light are projected on a white screen, the screen will appear white. Thus R + B + G form white light. • when R, G, B light form white light, this is the additive color process. • for this reason, R, B, G are primary colors of light. • the primary colors can be mixed in pairs to form three other colors: R+G yellow B+G cyan (aqua) R+B magenta (purple) These colors are called secondary light colors. • Black is the absence of reflected light. • Yellow is the absence of blue or opposite blue. Therefore, yellow and blue will produce white light. • Cyan is opposite red and magenta is opposite green. • Any two colors that combine to produce white light are complementary colors. • the subtractive color process: if you take yellow away from white light, you get blue. Yellow, magenta, and cyan are the subtractive primaries or primary pigments. • red, blue, and green are secondary pigments. Secondary pigments absorb two primary colors and reflect one. Red absorbs green and blue and reflects red. Polarization Light is a transverse wave that has two components. They are perpendicular ( ⊥ ) to each other. Polaroid material contains long molecules that allow electromagnetic waves of one direction to pass while absorbing the waves vibrating in the other direction. Some material (polarizers) only allow one component to pass while blocking the other. Therefore, the amount and intensity is reduced. ie. polarized sun glasses