Class Discussion about the Light Spectrum

Scenario Description: A class is in progress.  The topic is light.

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Role Dialog
NarratorA class is in progress.  The topic is light.
TeacherSo light exists as a range of light energies or frequencies or wavelengths.  We call this range of energies the “light spectrum”.
EricI don’t quite understand the “light spectrum”.  Can you give me an analogy to help me understand it?
TeacherCertainly.  Think of a piano keyboard.  Let’s say that the middle 7 keys are the colors of the rainbow. 
EricSo each key represents one of the colors of the rainbow?
TeacherExactly.  We have a mnemonic to help us remember the colors of the rainbow:  Roy G. Biv.
SamRoy G. Biv?  Who is he?
TeacherNo one.  It’s just a fake name to help us remember the rainbow colors in order:  RED-ORANGE-YELLOW-GREEN-BLUE-INDIGO-VIOLET
SamOh, that’s really clever.  What about the other keys on the piano keyboard?  What colors are those?
TeacherGood question.  The rainbow colors are what we call the visible part of the light spectrum, the light we can see with our eyes.  There are other “colors” of light that we cannot see.  We call this the invisible part of the light spectrum.
SamIf that light is invisible, how do we know it’s there?
TeacherScientists have developed instruments that can detect invisible light.
EricDoes invisible light have any use?
TeacherAbsolutely!  Since we can’t see invisible light, describing it with colors is impossible, so we refer to it in a different way.  Keys to the left of RED are called the infrared or IR part of the light spectrum.  “Infra” means “under”, “below”, or “less than” in this sense.
SamDoes that mean the keys to the right of the VIOLET key are called Over-Violet?
TeacherThat’s a very good guess!  However, we use the Latin prefix “ultra”, which means “beyond”, so ultraviolet or UV refers to the light spectrum to the right of VIOLET.
EricSo we have IR light, visible light, and UV light.  Is that right?
TeacherCorrect.  Can anyone think of any uses of IR light?
SamI think I’ve heard my dad mention that the TV remote control uses IR light and you have to point it at the TV to make it work.
Teacher Light travels in a straight line, so you have to point the tiny IR light transmitter at the TV’s light receiver to make sure it can see your coded light signal to control the TV.
EricI’ve also seen in some movies that the Army has night-vision goggles that can “see” IR light.  It looks strange though, all greenish.
TeacherThose are excellent examples of the real-life application of using IR light.  What about UV light?  Think women.
SamOh, that’s right!  My sister goes to a tanning salon to work on her “perfect” tan.  She mentioned that UV light is used in the tanning booths.  It’s kind of an eerie blue color.  Why is it blue if it’s supposed to be invisible?
TeacherCorrect.  UV light is the part of the sunlight spectrum that burns your skin when you get a sunburn.  We use a special kind of light bulb, called a black light, to produce UV light.  The color is just a function of the light bulb design and how it works.  The UV light itself is invisible but the “black light” that contains it produces a purplish-blue light.
EricWhat about night clubs?  I’ve seen them use black light.  Why do they do that?
TeacherBlack light has a strange characteristic that makes it produce a snazzy effect in a dark room, especially when dancing.  It makes white and fluorescent colors stand out as really bright.  We call dancing to this kind of black-light effect “tripping the light fantastic”.   UV light can also harm the retina of your eye.  The retina is kind of like a mini-projector screen in the back of your eyeballs.  And UV light helps plants grow.
SamI bought some sunglasses that came with a label that said they block UV light.  Is that to protect my, um, retinas?
TeacherExactly.  We divide the UV part of the light spectrum into UV-A and UV-B light segments.
EricSir, I’ve seen a piece of glass called a prism.  Somehow it is able to display a rainbow.  How is that possible?
TeacherAh, yes.  A prism is an ingenious little device.  It is triangle-shaped for a reason.  Light can travel through a medium, such as glass or water.  By following the triangular-shape of the prism’s glass, the light is bent at an angle.  When the light rays are bent, the light passes through different thicknesses of glass due to the design of the prism.  This causes the light to refract or split out into colors due to bending at different angles.  When this happens, we can see the various energy levels of light – what we have now come to know as Roy G. Biv.
SamSo a prism is basically a “rainbow-maker”!
TeacherThat’s one way to describe it, yes.
EricAnd when I spray a mist of water into the air?  Or after a rain?  Is the water in the air somehow acting like a prism to create a rainbow effect.
TeacherThose are superb examples that show you are beginning to understand the light spectrum and how it can be separated into its component parts.
SamWait a minute.  Something doesn’t make sense.  Why can’t I see these visible colors when I go outside?
TeacherSunlight contains all the colors of the light spectrum.  When they are combined together, they form what we call “white light”, which is transparent or invisible.  The prism effect proves to you that this white light indeed contains all the visible colors of the light spectrum.
EricSir, I know a song about light.  It’s called “You Light Up My Life”.  Do you know it?
TeacherIndeed I do, Eric.  My wife played that song at our wedding.  Okay, and on that note, let’s have a quiz to see what you remember about this topic.
NarratorThe class emits a collective groan.
Jehan A

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