Light energy short 2012
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    Light energy short 2012 Light energy short 2012 Presentation Transcript

    • Light Energy What is light? How does light travel? How is light reflected, refracted, and absorbed?How does light determine how we see the color of an object?
    • What is light?Light is a form of energy that can be released by an atom. It is made up of many smallparticles called light photons.Atoms release light photons when their electrons become excited. Electrons areparticles that move around an atoms center or nucleus. Electrons move in differentpaths around the nucleus. When something happens to an atom to add energy to it,like it gets heated, the electrons may jump to different paths. Soon they fall back totheir original path. When they return to their original path, they may release energy inthe form of photons of light .
    • How does light travel?Light photons travel in waves made up of electrical and magnetic energy. But, lightwaves can travel through space where there is no material. Light photons travel veryrapidly: 186,000 miles per second.
    • How does light travel?Electromagnetic waves include more than visible light. They also include cosmicrays, gamma rays, radio waves, and other forms of electromagnetic radiation. Weonly see some of this energy as visible light.
    • How do we see light?Any light that you see is made up of a collection of one or more photons travelingthrough space as electromagnetic waves. In total darkness, our eyes are actually ableto sense single photons, but generally the light we see in our daily lives comes to us inthe form of zillions of photons produced by light sources like the Sun or a flashlight.If you look around you right now, there is probably a light source in the room producingphotons, and objects in the room that reflect those photons. Your eyes absorb some ofthe photons flowing through the room, and that is how you see.
    • How is light reflected?Reflection is when incoming light hits an object andbounces off. Very smooth surfaces such as mirrorsreflect almost all incoming light.What you see in the mirror is reflected light. We now know this can’t happen!
    • How is light refracted?Refraction is when light waves change direction asthey pass from one material to another. Light travelsat different speeds as it passes through differentmaterials. Light travels slower in air than in a vacuum,and even slower in water. The change in speed bendsthe light.Different wavelengths of light are slowed at differentrates, which causes them to bend at different angles.For example, when the full spectrum of visible lighttravels through the glass of a prism or water dropletsin air, the wavelengths are separated into the colorsof the rainbow.
    • How is light absorbed?Sometimes when light hits an object, the atoms andmolecules in that object start to vibrate as they absorbthe light.When a dark surface like a black asphalt roadabsorbs light, it can get hot enough to cook an egg!Light energy has turned into heat energy that cooksthe egg.Darker colored materials absorb more light thanlighter colored materials. The same egg might notcook on a light grey cement sidewalk!
    • How is light reflected, refracted, and absorbed?
    • Why is the sky blue?The sky appears blue because of the scattering of light. Light at shorter wavelengths—blue and violet—is scattered by nitrogen and oxygen as it passes through theatmosphere. Longer wavelengths of light—red and yellow—transmit through theatmosphere.This scattering of light at shorter wavelengths illuminates the skies with light from theblue and violet end of the visible spectrum. Even though violet is scattered more thanblue, the sky looks blue to us because our eyes are more sensitive to blue light.The same thing happens in the ocean’s water, so it also appears blue.
    • How does light determine how we see the color of an object?Color refers to the different wavelengths of light in the visible light spectrum that oureyes can see.When we look with our eyes at an object, we are really seeing the wavelengths of lightthat are reflected by the object. The object absorbs the other wavelengths.The physical and chemical composition of matter in the object determines whichwavelength (or color) is reflected.
    • How does light determine how we see the color of an object?We see objects of a certain color because they reflect part of the light spectrum andabsorb the rest. So, the apple leaf appear green because it absorbs all the colorsexcept green. The apple skin appears red because it absorbs all the colors except red.The color we see is the color reflected by the object.
    • How does light determine how we see the color of an object?Color originates in light. Sunlight, as we perceive it, is colorless. In reality, a rainbow istestimony to the fact that all the colors of the spectrum are present in white light.When white light is bent or reflected, as through a prism, it can separate into thedifferent colors of the spectrum.A rainbow is white light that is reflected and bent by water droplets in the air, causingthe colors of the light to separate into a range of red, orange, yellow, green, blue, andindigo/violet.
    • How does light determine how we see the color of an object?A transparent material,such as glass, allows light topass through it very well.A translucent materialabsorbs some of the light.An opaque material allowsno light to pass through.
    • How does light cause heat?When the electromagnetic radiation from the sunencounters a material, it causes the atoms in thematerial to vibrate, generating heat and causing theobject to release thermal energy. Vibrating atomshit other atoms and heat is moved through amaterial.In heated liquids and gases, convection causesthe hotter material to move upward and the coldermaterial to sink.In heated solids, conduction between the closelyvibrating atoms moves heat through the materialevenly. So, don’t use a metal spoon to stir hotsoup!
    • How is heat measured?Heat is measured indegrees, using theCelsius, Fahrenheit,or another type ofscale.The movement of heatthrough a materialdepends on the sourceof heat and the type ofmaterial. Somematerials, like metals,move heat well byconduction. Wooddoes not conduct heatwell.
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