Light Energy. Name: Key

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Baldric Watts
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1 Light Energy Name: Key

2 What is Light? Make a list of things that give us light. How many can you think of? Answers will vary Count the items on your list. How many did you write? Light: Light is a form of energy that you can. see Light is one kind of. radiant energy Light comes from many different. sources Some items produce light, while others reflect light. Is it a producer or a reflector? Candle producer reflector Mirror producer reflector Sun producer reflector Flashlight producer reflector Jupiter producer reflector Name four other objects that produce light. fire lantern stars lamp Name four other objects that reflect light. Moon metal Earth water

3 Think About It: Where do you sit when you watch television? in front of it Demonstration: Laser Pointer Turn off the classroom lights. Carefully point a laser pointer at a wall. Clap chalk erasers together (or shake a nylon bag of flour) between the wall and the laser pointer. Record your observations: The chalk dust makes the laser visible. The laser light travels in a straight line. How Does Light Travel? Light travels in a. straight line Can you think of some real-life examples of light traveling in a straight line? Television, flashlight, laser, lamp, etc.

4 Light Experiments Experiment with each light source. Record the properties you observe on the chart below, then identify at least one real life use for each light source. Light Source Color of the Light Intensity or Brightness Heat Produced Illustrate how it Travels Real Life Uses Flashlight White Laser Red Find something in the dark. Point at something on a screen. Sun Yellow Light the Earth Blue Lightbulb Blue Party or holiday Etc

5 Reflection: Reflection Light can be reflected or absorbed by a surface. When light is, reflected it that bounces off surface. Example: mirror When light is, absorbed it is trapped by that surface. Example: body Light is reflected off a surface in a special way. Partner Activity: Bouncing Tennis Balls Illustrate what you observed while rolling, bouncing, and catching the tennis ball. Demonstration: Basketball Illustrate what you observed while bouncing and catching the basketball.

6 Light Reflection: The and tennis ball the basketball actually represent what happens to light as it is. reflected When light hits a reflective surface, like a, mirror it will at bounce back the. same angle The angle at which light strikes a surface is the. angle of incidence The angle at which light reflects off a surface is the. angle of reflection The angle of incidence is > < = the angle of reflection. Example: When light strikes a mirror at a 45 angle, it is reflected at a 45 angle. Draw and label an illustration of this property of light. Light Beam Angle of Incidence 45 Mirror 45 Angle of Reflection

7 Group Reflection Challenge: Reflection Activities Set Up: Stand the textbook up on the desk. Lay the flashlight on a desk facing one cover of the textbook. Turn on the flashlight, so you can see the light on the cover. The Challenge: Move the light from one side of the textbook to the other, but you may not move the flashlight or the textbook. You may only use the mirrors and what you know about light. Illustrate and label your solution. One possible solution: mirror mirror mirror textbook Class Reflection Challenge: Give each student a mirror. The teacher will carefully point a laser pointer into one mirror. Let s see if we can get the light to reflect in every other mirror in the classroom. What worked well? What didn t? Why? vary What would you do differently next time? vary What is our record for the most number of mirrors reflected?

8 Mirrors that Multiply: Use a hinged mirror. Test angle AOJ. How many faces do you see? 3 Test angle BOI. How many faces do you see? 4 Test angle COH. How many faces do you see? 5 Test angle DOG. How many faces do you see? 7 Test angle EOF. How many faces do you see? 11 O A J B C D E F G H I What pattern do you see? The larger the angle, the fewer faces. The smaller the angle, the more faces.

9 Butterfly Designs: Use one mirror to reflect portions of the butterflies to create new designs.

10 Reflection Experiments Experiment with each item. Record the properties you observe on the chart below. Item: Reflection Observations: TV Prediction: TV Result: Reflects Mirror Yes Yes Reflects Smooth Foil in one Yes Yes direction Reflects in Crumpled Foil scattered Yes No directions Does not reflect Sandpaper No No Does not Black Paper reflect No No

11 Reflected, Absorbed, or Transmitted? Light Transmission: Light that passes through matter is transmitted by the material. If light is not, transmitted some if it is. reflected If light is not transmitted or, reflected it is. absorbed There are three types of materials: Transparent: Light is transmitted (passes through) Translucent: Some light is transmitted, some is reflected and scattered Opaque: Light is absorbed (not transmitted) Transparent, Translucent, or Opaque? Use a flashlight to test each item. List it in the correct category. Examples: Transparent: Translucent: Opaque: glass Wax paper foil Plastic wrap Red cellophane cardboard water Tracing paper book Sandwich bag fabric Index card transparency Plastic food container Canning jar lid Test tube netting Paper cup Clear plastic cup box

12 Refraction Activity: Cup of Water Put your thumb in the glass of water. What do you observe? Put a drinking straw or pen/pencil in the glass of water. What do you observe? Thumb in Cup of Water: Straw in Cup of Water: Refraction: When an object is placed in a glass of water it appears to be. broken This is because of light. refraction Light changes direction when it enters a new. medium A medium is any substance through which a wave is. transmitted Example: Light is traveling from the overhead light bulbs through. air When the light enters the cup of, water it enters a new. medium This causes the light to change. direction Light in air travels. fast Light in water travels. more slowly When light, slows down it changes. direction When light changes direction or, bends it is called. refraction Refraction is caused by the change of the as speed of light it travels through different. mediums

13 Activity: Throwing Contest Who has a great throwing arm? Who won? laser Why? Speed of light Speed of Light: The speed of light is. 186,000 miles per second That is the same as 7 ½ times around the Earth in one second. This is how fast light travels in. air When it enters a new medium (like water), it slows down. The result is. refraction Appearing Coin: Look at the cup from the side so you can still see the bottom of the inside of the cup, but you cannot see the coin glued to the bottom. Slowly pour water into the cup until you see the coin appear. Why does it work? The coin didn t move. The cup didn t move. The water caused the light to bend and made the coin visible. It s refraction!

$Refraction Experiments Pour the correct amount of water into each glass. Place a drinking straw in each cup being sure the angle of the straw is the same for each container. Record your observations.$

14 Refraction Experiments Pour the correct amount of water into each glass. Place a drinking straw in each cup being sure the angle of the straw is the same for each container. Record your observations. 50 ml of Water 100 ml of Water 150 ml of Water 200 ml of Water Illustration: Illustration: Illustration: Illustration: Observation: Observation: Observation: Observation: Refraction Refraction Refraction bigger Refraction very obvious Pour 100 ml of each liquid into each glass. Place a drinking straw in each cup being sure the angle of the straw is the same for each container. Record your observations. Water Vegetable Oil Karo Syrup Rubbing Alcohol Illustration: Illustration: Illustration: Illustration: Observation: Observation: Observation: Observation: Refraction Refraction Refraction Refraction smaller same as water

15 Color of Light Light Waves: Light travels in. waves Crest 1 wavelength Amplitude Amplitude Trough Frequency is the measure of the number of waves that pass by a given point in one second. Remember, light is one kind of radiant energy. Radiant energy includes waves of all different wavelengths and. frequencies When all the types of radiant energy are arranged in, order we have the. Electromagnetic Spectrum The Electromagnetic Spectrum

16 Visible Light: We can only see one portion of the electromagnetic spectrum. That portion is called. visible light What color is the light from most light bulbs? white Although we see white light, it s actually made up of many. colors The colors of the spectrum are: red, orange, yellow, green, blue, violet An easy way to remember these colors in order is: ROY G. BIV Class Activity: Prism Glasses White light appears while to our eyes, but it is actually made up of the colors of the visible light spectrum. Let s use glasses with special lenses to help us see these colors. Record your observations. vary Class Activity: Prisms Prisms separate light into the colors of the spectrum. Use a prism and a flashlight to see if you can create a rainbow. What technique works best? Shine light on an edge. Is a prism the only way we see a rainbow? no When do you usually see a natural rainbow? after rain How was that rainbow created? What caused the sunlight to separate? The water vapor left in the air after a rain storm acts as a prism to separate the light.

17 Activity: Blending Light We can use a prism to separate the colors of white light, so we can see all the colors of the spectrum. Is it possible to blend the colors of light and make white? Let s find out. Record your observations. Primary colors of light = red, green, and blue red + green + blue = white light Colors: If light is made of all the colors of the spectrum, how do we see certain colors? Why do we see white, black, or red? r o y g b i v r o y g b i v r o y g b i v r White Black Red Why we see white: All colors strike, all colors reflected Why we see black: All colors strike, all colors absorbed Why we see red: All colors strike, red reflected, the rest are absorbed

18 Now try two on your own Why we see yellow: All colors strike, yellow reflected, the rest absorbed Why we see green: All colors strike, green reflected, the rest absorbed Summary: Light can be reflected ( ). bounced off Light can be absorbed ( ). trapped Light can be refracted ( ). bent Light can be separated ( ). creates rainbow

19 Color of Light Experiments Test each object according to the chart. Record the color observed. Object Color: Red Filter Orange Filter Yellow Filter Green Filter Blue Filter Violet Filter Red Red Red Red Black Black Dark red Orange Orange Orange Light orange Black Black Red orange Yellow Orange Orange Yellow Green Dark green Yellow Green Black Black Black Green Black Black Blue Black Black Black Black Blue Blue violet Violet Black Black Black Black Blue violet Violet White Red Orange Yellow Green Blue Violet Layer the colored filters and see what effects are created. Record your results. Answers will vary

3 Interactions of Light Waves

CHAPTER 22 3 Interactions of Light Waves SECTION The Nature of Light BEFORE YOU READ After you read this section, you should be able to answer these questions: How does reflection affect the way we see