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Chapter 16

Chapter 16. Fundamentals of Light. Ray Model of Light. Light is represented as a ray that travels in a straight path. The direction can only be changed by placing an obstruction in the rays path. Sources of Light. Luminous Sources: objects that emit light Sun, flash lights, candles

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Chapter 16

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  1. Chapter 16 Fundamentals of Light

  2. Ray Model of Light Light is represented as a ray that travels in a straight path. The direction can only be changed by placing an obstruction in the rays path.

  3. Sources of Light • Luminous Sources: objects that emit light • Sun, flash lights, candles • Illuminated Sources: objects that are visible as a result of light reflecting off of it • Moon, bicycle reflector • Opaque, Transparent, and Translucent are all used to describe how illuminated sources are visible

  4. Luminous Flux Luminous Flux is the amount of energy that a light emits. Unit: lumen (lm) A typical 100-W bulb = 1750 lm Illuminance is the rate at which light hits a surface. Unit: lux (lx) Equivalent to lm/m2

  5. Illuminance Inverse-Square Relationship The amount of light that hits a surface depends on the distance to the object. In fact it is an…..

  6. If I am standing 3 meters away from a light source, by how much does the illuminance change if I walk to 1 meter away from the object? • 9 • 0

  7. The speed of Light • Light was initially thought to travel at an instantaneous speed. • Galileo was the first to hypothesize that light has a finite speed. • Ole Roemer (Danish astronomer) was the first to find that light did travel with a finite speed. • In 1926 an American physicist, Albert A. Michelson used a set of rotating mirrors to measure the speed of light.

  8. Speed of Light Continued • Michelson’s measure of 2.997996 x 108 m/s won him the Nobel prize in science. The first American ever to accomplish this. • Today the speed of light, c, is given by 299,792,458 m/s. • For calculation purposes, c = 3 x 108 m/s • Light travels 9.46 x 1012 km in one year.

  9. Wave Nature of Light • In 1665 an Italian scientist observed that the edges of shadows are not perfectly sharp. • From this observation he realized that light was diffracted like all waves. • In 1678 a Dutch scientist Christiaan Huygens used this observation to argue the wave nature of light.

  10. Color • Newton used a prism to pass white light through. • Newton called this arrangement of colors a spectrum.

  11. Color Cont. • Since light was now proven to act like a wave, the wave equation is now applicable to use with light. • The range of frequencies for light are

  12. What is the frequency of a red light whose wavelength is 700 nm? • 4.28 x 1014 Hz • 4.9 x 108 Hz • 4.28 x 105 Hz • 4.9 x 10-1Hz

  13. What are the three primary colors of light? • Red, blue, yellow • Red, blue green • Magenta, cyan, yellow • Magenta cyan, green

  14. Color Addition of Light • White light is composed off all the different colors of the spectrum. • However, a combination of three colors with the correct intensities will produce white light. • These three colors are Red, Blue, Green. • These colors are known as the primary colors

  15. Color Wheel Yellow Magenta Cyan

  16. Addition of Color • Cyan, Magenta, and Yellow are called secondary colors because each is a combination of two primary colors. • Complimentary colors are two colors of light that can be combined to make white light.

  17. Color by Subtraction • The colors of objects are not only determined by the colors of light they reflect but also the colors of light they absorb. • Dyes and pigments are used to make materials absorb different colors of light.

  18. Color Subtraction • The primary pigments are • Cyan • Magenta • Yellow • Each pigment only reflects the color of light it is made of.

  19. If a white light is shown on an object that is made of a cyan pigment, what color will not be reflected off the surface? • red • green • blue

  20. Secondary Pigments • A pigment that absorbs two colors of light is called a secondary pigment. • Example: green pigment will only allow green light to reflect, therefore canceling out red and blue • Note that the primary pigments are the secondary colors and the secondary pigments are the primary colors.

  21. Polarization of Light • Why do we buy polarized sunglasses? • What exactly does it mean that they are polarized?

  22. Polarization • Light travels as a transverse wave, which means it’s particles vibrate perpendicular to the wave motion. • Polarization of light means to limit the direction in which light is allowed to vibrate.

  23. Polariztaion • In the picture above, the polarizer acts like a doorway, only allowing light that is traveling in a specific direction through.

  24. Reflection • When light reflects off of any surface, the light is polarized along the plane of the surface. • Example: light reflected off a road becomes horizontally polarized • When you wear polarized sunglasses, this reduces the “glare” from the cars and the road in front of you.

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