long wavelengths short wavelengths If you pass white light through a prism, it separates into its component colors. Spectrum R.O.Y. G. B.I.V !!
Dispersion • The separation of light into colors arranged according to their frequency, by interaction with a prism or diffraction grating.
Making Light • Incandescence • involves the vibration of entire atoms • the sun, fire and light bulbs • Luminescence • involves only the electrons • occurs at lower temperatures • florescent lights, neon light, mercury-vapor street lights, television screens and computer monitors, fire-flies
What is incandescence? • Emission of light by a solid that has been heated until it glows, or radiates light. • When an iron bar is heated to a very high temperature, it initially glows red, and then as its temperature rises it glows white. • Incandescence is heat made visible – the process of turning heat energy into light energy (Black Body Radiation)
Other examples of incandescence and its uses • The bright white colors of fireworks are examples of incandescence. • Metals, such as magnesium, are heated to white-hot temperatures during combustion. • The other colors produced in pyrotechnical displays employ luminescence, rather than incandescence.
Double Rainbow • Raindrops reflect the sun’s light noticeably inward from the rainbow arc, and correspondingly out of the secondary bow, so that the dark band is seen between the bows. • This effect, called Alexander’s band, was first described by the Greek philosopher Alexander of Aphrodisias in the 3rd century. • The sky below the primary (lower) rainbow, and above the secondary (higher) bow, is brighter as a result.
Terms You Need to UnderstandVocab Assignment:1) “Working Definition”2) Illustration3) Use the word in a sentence • Absorption • Reflection • Dispersion • Incandescence • Luminescence • Diffraction • Scattering • Refraction • Interference
Light Absorption • When photons of light hit atoms and cause them to increase their vibrations (causing them to heat up.) • A fabric that we see as black has absorbed all colors of the spectrum and is hotter than a white fabric that reflects all colors. • REMEMBER THIS AS YOU GET DRESSED THIS SUMMER!
Light Reflection • When an incoming light wave bounces off of an object.
What is light scattering? In the lab… When light bounces off of an object in a variety of directions.
Light Scattering In nature… red sunsets blue sky and clouds
Why is the sky blue? What Makes a Red Sunset?
Refraction • When light waves change direction as they pass from one medium to another.
How does the magic happen? • Index of refraction • linked to the speed of light in the material • The higher a material's index of refraction, the slower light travels in that material. • If a transparent object is surrounded by another material that has the same index of refraction, then the speed of light will not change as it enters the object. No reflection and no refraction will take place, and the object will be invisible.
Light rays Ocean Beach Fuzzy Shadow Diffraction of Light Diffraction is the ability of light waves to bend around obstacles placed in their path. Water waves easily bend around obstacles, but light waves also bend, as evidenced by the lack of a sharp shadow on the wall.
The Superposition Principle • The resultant displacement of two simultaneous waves (blue and green) is the algebraic sum of the two displacements. • The composite wave is shown in yellow. Constructive Interference Destructive Interference The superposition of two coherent light waves results in light and dark fringes on a screen.
s1 s1 s1 Constructive s2 s2 s2 Destructive Constructive Young’s Interference Pattern Bright fringe Dark fringe Bright fringe
What causes the color we see swirling about the surface of bubbles? It exists due to the varying thicknesses of the soap film. As light waves travel through the bubbles, the waves and their subsequent wavelengths react differently.
As the waves travel through the bubble they collide with each other. • If they collide crest to crest, then they reinforce each other’s impact and effects, causing constructive interference. • If the waves meet crest to trough, they cancel out each other’s effect, and the result is destructive interference.
Cool Interference • Responsible for the pearly luster of a shell, the colors of insect wings and the feathers of many birds, as well as the color of bubbles. • White light is separated into colors as it reflects from the two surfaces of a thin film. • Where the two reflections interfere constructively, they produce a band of color. Where they cancel each other, that color is subtracted from the spectrum.
What is a soap bubble? • A soap bubble is a very thin sheet of water sandwiched between two layers of soap molecules • The thickness of the film - or rather, its thinness - determines whether iridescence is apparent. • Light is reflected from both the inner and outer surface of the soap bubble.
When an incoming ray of light strikes the outer surface of a bubble, part of the light ray is reflected immediately, while the other part is transmitted into the soap film. After reaching the inner surface of the film, this transmitted light ray is reflected back toward the outer surface. When it leaves the bubble, it travels in the same direction as the ray that was immediately reflected and is, therefore, parallel to that ray.