Optics An Educator s Guide With Activities in Science - PDF document

31 With a Spectroscope Level: Grades (KÐ4), (5-8)Activity: 7 AB Objective Science and Mathematics Standards Theory Materials The student will be able to seewhat happens to light when it passesthrough a spectroscope.Science as InquiryPhysical ScienceProblem SolvingCommunicationConnectionComputation/EstimationMeasurement¥ spectroscope (one spectroscope forfour students)¥ light sources (sunlight,incandescent, fluorescent, cadmium,sodium, neon, mercury, helium, etc.)(See List of Catalogs, page 83.)¥ diffraction grating¥ compact discA spectroscope is a device that can beused to look at the group of wavelengthsof light given off by an element. Allelements give off a limited number ofwavelengths when they are heated andchanged into gas. Each element alwaysgives off the same group of wavelengths.This group is called the emissionspectrum of the element.In the visible wavelengths of theelectromagnetic spectrum, red, with thelongest wavelength, is diffracted most; andviolet, with the shortest wavelength, isdiffracted least. Because each color isdiffracted a different amount, each colorbends at a different angle. The result isa separation of white light into the sevenmajor colors of the spectrum or rainbow.A good way to remember these colors inorder is the name Roy G. Biv. Each letterbegins the name of a color: red, orange,yellow, green, blue, indigo, and violet.(Reference Electromagnetic Spectrumpage 34.) 32 (Students should color these boxes with their crayons.) ROGBIVRedOrangeGreenBlueIndigoViolet YYellow Procedures Use a spectroscope and look atdifferent kinds of light. View bulbswith different gases inside. Observations, Data, and Conclusions 1.Observe each source of light. Explainwhat you see.2.Observe the colors. Start with thefirst color on the left and list themin the table in the order that yousee them.3.When you look at the different lightsources through the spectroscope,observe the stripes of color. Do theyfade or blend into each other?Describe the bands of color.4.Does each light source produce thesame group of colors or spectrum?5.Each group of colors for each differentlight source is called the emissionspectrum for that source. How are thespectra or groups of colors alike?Different?6.Why are the groups of color for eachlight source different? ColorsLight Source 33 Optics: An EducatorÕs Guide With Activities in Science and Mathematics EG-2000-10-64-MSFC ActivitiesAdditional Activities White light can be separated intoall seven major colors of the completespectrum or rainbow by using adiffraction grating or a prism. Thediffraction grating separates light intocolors as the light passes through themany fine slits of the grating. This is atransmission grating. There are alsoreflection gratings. A reflection gratingis a shiny surface having many finegrooves. A compact disc makes a goodreflection grating.The prism separates light intocolors because each color passesthrough the prism at a different speedand angle. The angles of reflection ofthe light, upon entering and leavingthe prism, vary with the wavelength orcolor of the light. LightDiffracted Diffraction Grating RedVioletWhite LightPrism \f\t\r 34 The ElectromagneticFor hundreds of years, scientists believedthat light energy was made up of tinyparticles which they called Òcorpuscles.Ó In the1600Õs, researchers observed that light energyalso had many characteristics of waves.Modern scientists know that all energy isboth particles, which they now call photonsand waves.Photons travel in electromagneticwaves. These waves travel at differentfrequencies, but all travel at the speed oflight. The electromagnetic spectrumthe range of wave frequencies from lowfrequencies (below visible light) to highfrequencies (above visible light). (Seefigure below.)The radio wave category includes radio andtelevision waves. These low-frequency wavesbounce off many materials.Microwaves pass through some materialsbut are absorbed by others. In a microwaveoven, the energy passes through the glassand is absorbed by the moisture in the food.The food cooks, but the glass container isnot affected.Like other wavelengths, infrared or heatwaves are more readily absorbed by somematerials than by others. Dark materialsabsorb infrared waves while light materialsreflect them. The Sun emits infrared waves,heating the Earth and making plant andanimal life possible.Visible lightwaves are the verysmallest part of the spectrum and are theonly frequencies visible to the human eye.Colors are different within this category,ranging from the red wavelengths, whichare just above the invisible infrared, toviolet. Most of the SunÕs energy is emittedas visible light.The Sun also emits many ultravioletwaves. High-frequency ultravioletwavelengths from the Sun cause sunburn.X rays can penetrate muscle and tissuebut are blocked by bone, making medical anddental x-ray photographs possible.Gamma-ray waves, the highest frequencywaves, are more powerful than x rays and areused to kill cancerous cells.The atmosphere protects Earth fromdangerous ultraviolet, x-ray, and gamma-ray radiation. 1 km1 cm1 cm