Unit 6P.2: What is? Shadows Reflection The colors of the rainbow Science skills: Observing Classifying Predicting By the end of this unit you should: Know that light moves in straight lines. Know how shadows are formed. Know that light has a very high velocity. Know how we see things. Know that objects can absorb or reflect light. Know what the white color is. 132
6.16.1, 6.16.2 Physical Processes What is? Can you imagine what the world would be like without light? You would not be able to see the world around you. Plants could not grow, and you would not have any food to eat. is all around you, but maybe you don't think about it very often! has some very special things about it. is a form of energy. Some objects make light, such as the sun, a candle, a big fire or a light bulb. We call these sources of light. Sources of light actually glow. If you put them into a completely dark room, they would still glow and you would still be able to see them. These are examples of sources of light. Sources of light are objects that give out light 133
There are other things that look as though they are sources of light because they appear to shine, such as the moon, mirrors and aluminum foil. These are not sources of light, but they reflect the light that shines onto them (illuminated objects). If you put them into a completely dark room, they would not glow and you would not be able to see them. Can you think of another object? Moon Aluminium Foil Mirror The pictures a above show illuminated objects Illuminated objects are objects that reflect the light 134
Sources of - Look at the table below, Identify which of the following are light sources, circle the Sources of ONLY. Diamond The Sun CD The Moon Television Swords Candle Rainbow Mirror ning Firefly Bulb Cat s Eye Fireworks Eyes 135
Facts about light: Speed of light: Activity: Thunder and lightning. During a thunder storm, do you see the lightning first or do you hear the thunder first? You see the lightning before you hear the thunder. They happen at the same time but the thunder takes longer to reach your ears. Some kids were discussing what they felt after they saw a storm! Who do you think is right? travels very fast faster than sound 136
travels very quickly. is much faster than sound. When you put your torch on, the light leaves the bulb and hits the wall, it takes a very very very small amount of time. The time taken for the light to leave from here..and then hit the wall here feels like it take no time! But it does. The time taken for the sun s light to reach us taken about 8 minutes! It travels 150 million km!!! If you had a powerful flashlight 137 And shone it to the moon it would take about a second to reach there!
How does light travel? When a can with holes, is placed over a candle, light will shine through the holes. If we sprinkle chalk dust into the air around the can, we will be able to see how the light is traveling You can see the same effect when using the data show in a dark room. If you look up at the projection beam, dust in the air will show the beam of light traveling straight to the screen. 138
Activity: How Travels You will need: torch, boxes, rubber tube (ie shoes), and cardboard. Steps: Construct the boxes shown in pictures. Experiment 1: Down the tube 1 Look down one of the rubber tubes. 2 Change the shape of the tube until you can see light at the other end. What shape must the tube be for you to see the light? Experiment 2: Making a path 1 Move the two sliding panels until the light comes out of the hole nearest you and enters your eye. 2 Take the lid off the box. What do you notice about the four holes? Experiment 3: Shadows - you will need some paper and scissors 1 Turn on the light source. 2 Make a circular shadow on the screen. 3 Make the circular shadow bigger. 4 Make a square shadow on the screen. 5 Make the square shadow smaller. 139
Conclude - Discuss the following questions in your group. Use your observations to back up your conclusions. What did you use to make: a. the circular shadow? b the square shadow? What did you do to make the shadow: a larger? b smaller? travels in straight lines Key words Sources of light Reflecting light Speed Thunder Key Ideas Objects that give out light are called sources of light. Some objects reflect light. is very fast travels in straight lines. Straight line 140
Project Using a torch, water bottle with a sprinkler. Design an experiment to see how light travels. Q(1) Classify the following according to whether they are illuminated objects or sources of light. The Sun, the Moon, a star, the planet Jupiter, a laser, a mirror, a light bulb, a fire. sources of light illuminated objects 6.16.1 Shadows in more detail We know light travels in straight lines. When light hits a transparent object, like glass, it can pass through. 141
When it hits an opaque object, like wood, it cannot pass through and a shadow is formed. A shadow shows us where the light has not passed through an object, so the shadow is the same general Shadows shape are as formed the object. when opaque objects block the light source of light. You can make a shadow using a powerful torch and cutting out a shape on a piece of thick card! Make an animal you like! Even use your hands! The cat puppet blocks the light and a shadow is formed on the screen. Using a ruler and a pencil, we can draw a diagram to show where the shadow is made. 142
Activity: Making shadows. You will need: Torch, pencil/straw, clay. Steps: 1- Make an animal shape using clay. 2- Hold the torch above the object and shine it straight down? What do you observe? --------------------------. 3- What happens when you shine the torch to the side of the object? ------------------------------------------------- Move your flashlight in a circle above the object. What happens to its shadow (length and direction )? ------------------------------------------------- ------------------------------------------------- Shadows made by sun light: On a sunny day you will see many shadows. This shade is the shadow formed by the tree blocking the sun light. 143
Have you ever wondered how people discovered how to tell the time? They used the position of the Sun in the sky to mark the shadows on sundials. You can tell the time by looking at the shadow cast by the Sun as it shines on the pointer of a sundial. The proper name for the pointer is a gnomon. Make your own Sundial/Gnomon: 1. In pairs stick a pencil or straw on a plain piece of A4 paper. 2. You can use sellotape and clay to fix it in the position. 3. Go outside where the sun is shining. 4. Place the paper in the sunlight 5. Mark the shadow on your paper with a line and write the time above it. 6. After 5 min look at your paper again the shadow should have moved! 7. Repeat step 5. 144
Key words Shadow Sundial Key Idea Shadows are formed when the light hits something opaque and it cannot travel through. Key Questions Q(1) How is a shadow formed? --------------------------------------------- Q(2) Underline the right word: can travel through (transparent/ opaque) materials. Q(3)This picture shows the sun casting light on a round object. Label the diagram. Shadow source Object 145
Shadows Use the words in the box to fill the gaps below! shorter opposite longer larger smaller 1. The nearer the object is to the light source the the shadow. 2. The higher the light source the the shadow. 3. The closer the object is to the light source the the shadow. 4. The lower the light source the the shadow. 5. The shadow is always on the side of the object to the light source. 146
6.16.3, 6.16.4 Physical Processes Reflection We see only when there is a light source. We can see the sun because it gives out light which shines into our eyes. The candle flame is a light source when light travels from the candle flame into our eyes, we see the flame. There are other things that we can see but they are not sources of light. They reflect the light that shines on them, we say they are illuminated. The light hits the rabbit and bounces off. Then the light enters our eyes and we see the rabbit. 147
The light from the lamp hits an object and bounces off, then enters our eyes and allows us to see the object. Not all materials reflect (bounce) light in the same way: Type Definition materials reflect light that shines on Shiny materials them without scattering the rays. They usually have a smooth surface materials scatter the light rays and Dull materials reflect them in different directions. They usually have rough surface. materials do not reflect the light rays Dark objects well because they absorb the light. Shiny objects reflect the light better than dull objects. 148
Activity: Go round the school or science area with a torch and write down as many objects you could find that had reflective surfaces: Object and location. I can see my face It reflects torch light Mirror windows from outside Is this object made from this material because it is reflective? Why? Yes. Mirrors are very reflective so that you can see your reflection clearly. 149
Key Words Illuminated Reflect (bounce) Shiny Scatter Dull Dark Key Ideas We see objects when light from them enters our eyes. Materials can be shiny, dull or dark. Key Question Q1: Explain why we can see objects during the day but we cannot see the same objects when it is dark. ------------------------------------------------- ------------------------------------------------- Q2: Tariq dazzles his friend at the other side of the classroom by reflecting sunlight from his watch. Tarik s arm is lit up by the Sun. Explain why everyone can see his arm but only his friend is dazzled by his watch. ------------------------------------------------ ------------------------------------------------ ------------------------------------------ 150
6.16.5 Physical Processes The colors of the rainbow. White light is made up of many colors mixed together. A prism can separate the colors. The light BENDS twice, once when it passes from air into glass and again when it passes from glass into air. Rain drops act like prisms to form rainbows. It shows us that white color is not just one color. It is lots of different colors mixed together. The colors of rainbow are: Red, Orange, Yellow, Green, Blue, Indigo and Violet. 151
Activity 1: Making rainbow You will need: Small mirror, Clear glass, Water, and Flash light. Steps: 1. Gently place the mirror into the glass. Slant it up against the side. 2. Fill the glass with water. (picture A) 3. Set the glass on a table. Turn out the lights. Make the room as dark as possible. 4. Shine the flash light into the glass of water. Aim for the mirror. Adjust your aim until the light hits the mirror. 5. Observe what happens to the light in the glass. Look at the light where it hits the ceiling or the wall. Record what you observe. (picture B) 152
Making white light from coloured light You will need: White cardboard, Scissors, (120 cm works well), Pencil, Steps: 1- Cut out the circle on the right using some scissors. 2- Colour in the segments using colouring pencils. 3- Stick blu-tack on the back of the disc in the middle. 4- Stick the end of a pen or pencil into the blu-tack. 5- Hold the pen in between your two hands and rub them together to make the disc spin. 6- What colour do you see when the disc is spinning?------ is made up of coloured light. Mixtures of coloured light is combined to form white light. and color of objects: 153
The colors of object that you can see are the colors of light that the objects reflect. 154
Key Words Illuminated Reflect (bounce) Shiny Scatter Dull Dark Prism Rainbow Key Ideas We see objects when light from them enters our eyes. Materials can be shiny, dull or dark. White light is made up of many colors mixed together. The colors of object that you can see are the colors of light that the objects reflect. 155
Key Questions 1. Look at the picture below. Draw direction arrows on the beam of light to show how the girl can see the balloon. 2. Complete the sentences below to explain what is happening in the picture. a. The light travels from the to the balloon. b. The light bounces off the balloon and enters the girl's 3. What are the colors that make white light? 4. Which color will reflect from the balloon? 156
wordsearch Below are some words associated with. Can you find them all? S R A I N B O W B D E H L S A O P R L A F V A M S L R E I R G N R D W T T F G K T A G C O Y Y L H T O D I M C W U E T R R C I E N S S C Y E C F B R I G H T H L H H O W M P G H D K S I P Q J O S U N I T U T F H I Q B T J L U M I N O U S H U Bright Sun Reflect Rainbow Dark Torch Shadow Dim Luminous 157