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Details of light Properties. Bellringer – 2 mins to hand in. Describe why you think rainbows sometimes pop up after it rains. DO WORK. STOP. Objectives. Be able to fully explain exactly how rainbows, sunsets, sunrises, polarization, and diffraction work. Labs.
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Bellringer – 2 mins to hand in • Describe why you think rainbows sometimes pop up after it rains. DO WORK STOP
Objectives • Be able to fully explain exactly how rainbows, sunsets, sunrises, polarization, and diffraction work.
Labs • Pass up your completed labs. • If you still need lab data see me after class to arrange a time for you to come in to collect it.
Homework • Remember the long answer is due on Friday. • Also if you never turned in a completed answer sheet you have to see me before you leave school today. Otherwise I need to tell your parents/guardians that you are refusing to prepare for the Regents exam.
Dispersion • The separation of white light into a spectrum of colors is called dispersion. • The violet light is refracted more than red light.
Dispersion • This occurs because the speed of violet light through glass is less than the speed of red light through glass. • Violet light has a higher frequency than red light, which causes it to interact differently with the atoms of the glass. • This results in glass having a slightly higher index of refraction for violet light than it has for red light.
Rainbows • A rainbow is a spectrum formed when sunlight is dispersed by water droplets in the atmosphere. • Sunlight that falls on a water droplet is refracted. • Each color has a different frequency so they are all refracted differently resulting in dispersion.
Rainbows • Although each droplet produces a complete spectrum, an observer positioned between the Sun and the rain will see only a certain frequency of light from each droplet.
Rainbows • The rainbow we see depends on the relative position of the Sun, the droplets, and the observer. • So technically no two people can see the same rainbow at the same time.
Second-Order Rainbows • The second order is outside of the first. • It is also fainter and has the order of the colors reversed. • Light rays that are reflected twice inside water droplets produce this effect.
Third and Fourth Order • These are very rare to see • How many reflections in the water droplet of the third order? • 3 • From top to bottom, what are the order of the colors in a third order rainbow? • Same as a first order rainbow
Alexander’s Band • The region between the first and second order rainbows is noticeably dark. • This is because at this angle the water droplets won’t reflect/refract/disperse any light back to your position.
Electromagnetic Radiation • Light is an electromagnetic radiation • Electromagnetic radiation is a fundamental phenomenon of electromagnetism, behaving as waves propagating through space, and also as photon particles traveling through space, carrying radiant energy.
Polarization • Most glares are horizontally polarized light, so sunglass designers make their lenses vertical polarizers, thus block the horizontal glares from being transmitted to your eyes. • Demos
3D Tv and Movies • Appear blurry without glasses because you are seeing the two types of polarized light. • Each eye only needs one type of polarized light.
Scattering in the atmosphere • Because the wavelength of blue light is roughly the size of an atom of oxygen, blue light interacts with the oxygen and is scattered by it, while red light, with its longer wavelength, goes right passed the oxygen atoms. • If the Earth had no atmosphere, the Sun’s light would travel directly from the Sun in a straight line towards our eyes and we would see the Sun as a very bright star in sea of blackness. • But because the Sun’s blue light is scattered by the oxygen in the atmosphere, blue light from the Sun enters our eyes from all sorts of different angles and we see the entire sky as blue. • The atmosphere scatters violet light even more effectively, but our eyes are more sensitive to blue.
Sunrise/Sunset • At a low angle most of the blue light is scattered so much it never reaches your eyes because it has more atmosphere to go through. • This leaves the red colors to shine right towards your face • The red light is still not scattered, because it still doesn’t scatter in oxygen. • You can now start to see the violet light because the blue is missing.
Absorption • Why do black cars heat up faster and get hotter than white? • Black paint absorbs most of the light energy while white paint reflects and scatters most of the light energy. • This extra energy changes into excess heat inside of your car.
Light interference • Scientists debated for years and years whether light was a wave or a particle. • Between 1801 and 1803, English physician Thomas Young worked on and was able to convince nearly everyone that light was a wave. • This is known as the double slit experiment
Diffraction • Diffraction: the process by which a beam of light or other system of waves is spread out as a result of passing through a narrow aperture or across an edge, typically accompanied by interference between the wave forms produced.
Double slit experiment • Young took light from a small source and passed it through two closely spaced slits and produced an interference pattern. • https://www.youtube.com/watch?v=Iuv6hY6zsd0
Diffraction variables • Diffraction depends on the wavelength of the wave, and the width of the opening.
Diffraction and Wavelength • A shorter wavelength means less diffraction • A longer wavelength means more diffraction • For example red light has a longer wavelength than blue light so it will diffract more. This means the angle between its paths of constructive interference will be greater.
Single Slit experiment • Why do we still get interference through a single slit? • http://www.acoustics.salford.ac.uk/feschools/waves/diffract3.php
Huygens Principle • Huygens Principle • Argued that a wave front is a series of wavelets • Once the wave front hits a boundary the ends act as single point waves instead of a front and cause a circular pattern. • Now there in an interference pattern created.
Diffraction • Scientist use diffraction patterns to determine the atomic structure of mystery crystals. • You can also create a diffraction pattern that produces a cool image instead of dots.
