Unit 3P.2:Shadows, mirrors and magnifiers

Transcription

1 Unit 3P.2:Shadows, mirrors and magnifiers Shadows Mirrors and magnifiers Science skills: Predicting Classifying Observing Experimenting By the end of this unit you should: Know that shadows occur when a light source is blocked by an object. Know that the shape of the shadow is similar to the shape of the object that it makes. Know that mirrors reflect light and magnifying glass to focus it. 53

2 3.11.1, Physical processes Shadows Think of a time when you saw a shadow. What shape did it have? What made the shadow? Light comes from the sun, fire or a light bulb. A shadow is made when something blocks the light. Sharp shadows are visible on sunny days. 54

3 Activity Materials Chalk Optional- Camera Process Skills Observing Experimenting Enquiring Steps: 1- Go outside in the playground and find different shadows 2- Use the chalk to trace around a friends shadow. Take a picture of the shadow outline with a camera. 3- Find another location and repeat the activity Time to think: Q1-Circle which sense we use to detect light. Smell Taste Hearing Sight Touch Q2-Name 3 places where light can come from? Q3-What two things are needed to make a shadow? 55

4 Activity: Materials Plasticine Pencil Ruler Hoop Process Skills Observing Measuring Steps: 1. Choose an open area in the playground (not near buildings or trees) 2. Find a clean surface area to attach the plasticine and pencil as shown in picture. Place the hoop around the pencil to protect your experiment. 3. Record the length of the shadow at 3 different time during the day. Pencil length: cm Time Length of shadow (cm) 8 O clock 11 O clock 2 O clock 56

5 The position and shape of a shadow are dependent on the position and angle of the source of light. Think: Draw a line matching the object to the shadow. 57

6 Activity: Materials Torch, cardboard tube and teddy bear. Process Skills Observing Experimenting Enquiring Steps: 1- Shine the torch so that the beam goes through a cardboard tube. 2- Place the teddy bear at the other end of the tube. Show that the teddy bear blocks the light completely. Write what you observe? 3- Move the teddy bear slightly away from the end of the tube. What do you observe with the size of the teddy bear's shadow? Can you make the shadow big or small? How? 58

7 4. Experiment using the torch to observe the shadow effects on other objects when you move the torch up/ down, closer/ further away, side to side or make the light brighter/ dimmer. Now complete the sentences: 1- The nearer the object is to the light source, the the shadow is. 2- The further the object is from the light source, the the shadow is. 59

8 Light travels in a straight line Activity: Steps: Materials Torch 3 paper cards with holes cut in them Process Skills Observing Experimenting Enquiring 1- Give each group of students 3 paper cards with a small hole in them and a torch. 2- Ask students to arrange the cards so that light from the torch passes through the hole in all three cards. 3- Move the middle card. What happened? 4. Illustrate what happened to the torchs light path when; a. all the cards where lined up? b. the middle card was moved? 60

9 3.11.3, Physical processes Transparent, translucent and opaque materials. Transparent materials allow light to pass through easily. Opaque materials do not allow light to pass through and form a shadow. Translucent materials allow some light to pass through. Look at the candle behind each material below. A B C Identify the type of material of A, B and C; A B C 61

10 Activity: Materials Torch Various samples; fabric, cardboard, tissue paper, glass, aluminum foil etc Process Skills Observing Experimenting Enquiring Steps: Use the torch to test and sort these materials. Lets light go through clearly (Transparent) Lets some light go through (Translucent) Does not let light go through at all (Opaque) Extension: Select your own samples from the room to classify in the table above 62

11 Key terms: Transparent Opaque Translucent Key ideas: Shadows occur when a light source is blocked by an object. The shape of the shadow is similar to the shape of the object that makes it. Light can pass through a transparent object but not through an opaque one. Key Questions Q1.Indicate true or false for the statements below; a. A shadow is formed when the light is turned off. b. A shadow is formed when the path of light is blocked by an opaque object. c. A shadow is formed when an object falls to the floor. 63

12 Q2 Draw a shadow for each of the objects below; What happens to the shadow when the light is further away from the ball? 64

13 3.11.5, Physical processes Mirrors and Magnifier Your mother bought you new clothes and you put them on. Now you want to see yourself in the new outfit. How can you do this? You will use a mirror. A mirror is an object that reflects light. It is made from a sheet of glass. The smooth back surface of the glass is painted with silvery paint. When you see yourself in a mirror, light rays bounce (reflect) from you to the mirror and back again. 65

14 Activity: Materials Mirrors Torches Chalk Process Skills Observing Experimenting Enquiring Steps: 1. In groups of three you will need one torch, one mirror and a piece of chalk. 2. Select a few focus points around the room ie, the teachers desk, or a poster or the wall. 3. Each group will place their torch in a fixed position. 4. Turn off the lights. 5. Ask students to move the mirrors to reflect the torch light to the chosen focused point. 6. Use the chalk to draw the path of light from the torch to the mirror and to the focus point. 7. Repeat with the other focus points. 66

15 Other materials that can reflect an image. Mirrors are very shiny and smooth and reflect images very well. Other materials may have bumpy surfaces which reflect unclear or distorted images. Metal Water Glass Uses of mirrors We use mirrors in different ways such as in Cars cameras, telescopes, Over-the-sink in the bathroom mirrors, dental mirrors and fun-house mirrors with wavy surfaces. 67

16 Activity: Materials Mirror, spoon, shiny metal kettle Bucket of water Process Skills Observing Experimenting Steps: 1. Look at your reflection in each of the objects and draw what you see in the table. Mirror Spoon Water Kettle 68

17 Periscope An instrument that has angled mirrors or prisms and allows objects not in the direct line of sight to be seen, often used on submarines. 69

18 Kaleidoscope A kaleidoscope is a circle of mirrors containing loose, colored objects such as beads or pebbles and bits of glass. Magnifiers A magnifier is a lens that is used to produce a magnified image of an object. 70

19 Activity: Materials Magnifying lens/ glass Various objects ie. fabrics, skin, textured paper, brick. Process Skills Observing Experimenting Steps: 1. Choose a magnifying lens and three objects 2. Use the magnifying lens to observe the objects. Object 1 Object 2 Object 3.. What do the objects look like without the magnifying lens? 71

20 Time to think: How do magnifying lens change things? When are magnifying lens used? Put a or a x where a - Reading fine print - Coin collecting - Close inspection of artwork and paintings - Close inspection of passports, driver's licenses. - Reviewing medical records -Close inspection of mammal hair - Reading prescription bottles - Looking at skin injuries - Reading land maps -to focus light on an object 72

21 Look at the picture. A magnifying lens is used to focus light on an object. What will happen to the wood? Why does the wood burn? Because the magnifying lens focuses light as well as heat. 73

22 Key terms: Reflect Kaleidoscope Periscope Focus Magnifier lenses Key ideas: Mirrors are used to reflect light. Magnifying lenses are used to focus light. Key Questions Q1 Use a ruler to draw how the path of light moves through the periscope. You will need to use straight lines and remember to put the mirrors in! Q2- What happens at the focus point on the piece of paper? 74