Transcript Optics
Optics Val Bennington October 2008 Path of Radiation (Light) Can be modified: • Reflected • Scattered • Absorbed Or path may remain the same: • Transmitted Reflection • If reflected, all wavelengths hitting an object at one angle will be reflected along the same path • Angle of incidence = Angle of reflection • Does not spread the colors of visible light! Refraction - How Light is Scattered • Separates different colors!!! • Path through object DEPENDS ON WAVELENGTH !!! Review on Visible Light • Violets and blues are higher energy • Red has longest wavelength • Blue / violet has shortest wavelength Snell’s Law • Light slows when entering medium of higher refractive index • This causes the path of the light ray to bend toward the normal n1sin1 = n2sin2 Snell’s Law Continued… n1sin1 = n2sin2 n depends on wavelength ! When exiting a medium, light bends AWAY from normal (reverse the ray directions) Why is the sky Blue? • The atmosphere scatters visible light, so we receive direct light (from the direction of the sun) and diffuse light (from all directions). • The atmosphere more effectively scatters shorter wavelengths (blue) than longer wavelengths (red). • Thus when the sun is high in the sky, away from the sun the sky appears blue. • At sunset, sunlight must pass through a larger amount of atmosphere, enough so that red light is also scattered resulting in a red sky/clouds near the horizon. Rainbows Rainbows • Notice that violet and blue light are most bent (scattered) in the raindrop • Blue light and shorter wavelengths are MOST SCATTERED by raindrops and other aerosols in the atmosphere • Red light is least bent or scattered Rainbows cont. Dispersion • Light is dispersed when traveling through the raindrop • In other words, colors are separated • The path of each wavelength is changed, spreading the colors Halos • Light travels through ICE CRYSTALS when a halo is formed • Ice crystals randomly oriented (not all facing one direction) • Sun’s rays bent 22˚ • Sun’s rays appear TO YOU to be coming from around the sun Sundogs (mock suns) • If ice crystals mostly or all oriented with flat faces horizontal, sundogs appear Hand covers actual sun Other Phenomena • • • • • • Mirages (due to temperature gradient) Green Flash Sun Pillar Coronas Glories Broken Bow Extra Credit • Up to five points to write a paragraph about one of: Sun Pillar, Coronas, Glories, Broken Bow, or Green Flash • Draw a diagram of the observer, the light source, and how the light is bent, reflected, or scattered • Expect more than the couple sentences in the book, although feel free to use the textbook as a start • Make sure to explain how and why the light is bent and why light appears to be coming from a certain direction to the observer • List references on your extra credit sheet (make sure if it is from the internet, that it is from a university or research website) • Hand in your Extra Credit at start of class next week