Grade 4 Science

Optional Unit: Light

1. Identify ways that other forms of energy can be converted into light.
2. Investigate how light can be converted into heat.

1. Develop a variety of ways to change the direction in which light travels.
2. Observe how shadows are formed.
3. Examine the characteristics of images in a plane mirror.
4. Observe the refraction of light.
5. Identify ways in which lenses are used.
6. View the spectrum that forms when sunlight passes through a prism.
7. Infer what happens when sunlight passes through a colour filter.
8. Observe what happens when two different colours of light combine.
9. Predict what will happen when coloured objects are viewed using different colours of light.
10. Infer why objects appear to have a certain colour.

Introduce key vocabulary: light, energy, heat, shadows, colour, images, lenses, filter, reflection, refraction, transparent, translucent, opaque, spectrum, prism.

1. Post these words and have students match meanings, or
2. have students investigate definitions, or
3. have students and/or teacher suggest activities to demonstrate meaning. Language Arts activities such as writing riddles, writing about light and its uses, or developing different types of poems could extend the vocabulary of students.

1. How are heat and light related? Discuss examples of this relationship (sun, fire, light bulbs, lamps, stars, lightning, flashlights, etc.).

2. Are there other sources of energy that can be used to create light? (electricity, wind and water generators, electromagnets, etc.)

3. How can other forms of energy be converted to light?

1. Light rays can be bent.

   Place a pencil in a glass of water. Observe the pencil from different angles. What do you observe? Fill an aquarium or a clear rectangular container with water. Experiment with putting objects in the water (coin, rod, floating object, etc.). Look at these objects from straight above, from the side, from an angle, or from beneath if possible. Predict what you will see? What observations can you make? Cover the front of a flashlight with several layers of masking tape. Poke a hole near the centre of the tape to allow a thin beam of light to shine through. Darken the room. Focus the light straight down into the water, at an angle, from the side, etc. What do you see? Does what you see change if you observe from a different angle?

   Create a "light bender" with a shoebox, a square jar of water, and a flashlight. Make a slit in one end of the shoebox through which to shine the light in a slightly darkened room. Set the square jar of water in the centre of the box. What happens to the beam of light? Discuss.

2. Transmission of light through materials.

   Light a candle and set it securely on a table. Collect a variety of materials--glass, cardboard, wood, frosted glass, plastic, a clear rectangular container of water, etc. Holding each of the materials between your eye and the candle, observe whether the light is transmitted through the material. Record your results. Introduce the terms transparent, translucent, and opaque.

3. Reflection

   Using a flashlight in a slightly darkened room, shine a beam of light at an angle onto materials lying on a table surface--rough cardboard, a mirror, glass, smooth wood, sandpaper, light-coloured paper, etc. Notice the angle of the light from the flashlight and the angle of reflection from the given surface. Notice the reflected light on the ceiling or wall. Record and discuss results.

4. Colours in Light

   Using prisms in a darkened room allow only a small beam of sunlight to shine on the prism. Locate the band of colours on the wall. What colours do you see? If you have different colours of glass available (coloured sunglasses or pieces of cellophane will work), look through each of the different colours of glass at your colour spectrum. What do you observe? Why? Ask students to do some research, if necessary, to obtain satisfying answers. If you have the primary colours of light (red, green, blue) in pieces of cellophane, overlay corners of each to create secondary colours. Discuss the results. What colour do you get when all three colours are together? Use two (or three) flashlights and primary coloured cellophane pieces to experiment with combining colours. Predict results before you do the experiment. Cover the ends of the flashlights with red and blue cellophane. Shine them individually first and later together so that the light is on the same piece of white paper. What colour do you see? Repeat with red and green? blue and green? Are the combined colours of light the same as the combined colours with paint? Discuss. Record results. If you have other colours of cellophane, experiment by combining other colours. Are you able to create white?

5. Use a projector and petri dishes with water and added food colouring so that dishes may be stacked to experiment with colours and light. Have students predict results prior to use of various colours or combinations of colours.

6. Use a projector to create shadows of objects. Observe the shadows as the object is placed close to the light source and farther away. Discuss findings.

7. Light travels in straight lines. Use three index cards folded in half so that they will stand upright. In the centre of each (through both layers) punch a hole. Line up the cards so that a beam of light from a flashlight may be shone through the holes onto another card without a hole. Move one card slightly aside. Will the light still pass through all the holes? Discuss.

As an independent activity a student(s) may wish to research the use of shadows, sundials, telling time, etc.

1. Investigate the use of concave and convex lenses and how each affects the bending of light rays. Look at print through each lens.

2. Use magnifying glasses. What type of lens do they contain?

3. Examine print through droplets of water on clear plastic (overhead, or cutoffs from laminating). What do you observe? How does the size of the water droplet change the size of print?

4. Shine light from a flashlight through different lenses. What happens to the light?

5. Brainstorm ideas about the uses of lenses today. Record in chart form. Pictures may be drawn or cut out and pasted on charts to further develop ideas for uses of lenses. Students might also use this as an independent challenge to come up with further uses of lenses. Lenses are often used in glasses, binoculars, cameras, telescopes, microscopes, watches, headlights of vehicles, periscopes, magnifiers, etc.

1. Look in a mirror. What do you notice about the image? Look from an angle. What do you see? Pin holes allow one to examine objects close up. Make a small hole in the centre of a piece of cardboard. Look at objects through the hole--pencil, light bulb, finger, print, etc. Vary the distance at which items are held. What observations do you make?

2. Provide two mirrors which children can hold a various angles to examine images. Place any small object (crayon, eraser, marble, pasta, etc.) between the two mirrors which face one another. Gradually move one mirror so that the angle varies. What images do you see? Do you see more images of the object when the mirrors are close or far away? This activity may be used to have students write multiplication equations using different numbers of objects and different angles of the mirrors to produce repeated images.

3. Create a pinhole camera using a shoe box into which a small hole has been made at one end (use the end of a pin) and a small peep hole (end of a pencil) in the other. Create a frame from cardboard just large enough to fit snugly crossways in the box. Cut out the centre of this cardboard rectangle and cover the opening by taping a piece of wax paper or tissue paper over it. Tape securely. Place the cardboard frame into the box about one-third of the distance from the pinhole to the peephole end. Secure in place. Put the lid on the shoe box. Look through the peep hole at a light source such as a bulb or lighted candle. What do you see? Record your observations.

1. Try creating spectrums of colour using marbles, glass beads, bits of glass, gems, such as those in a ring, different prisms, etc. Do you always get the same band of colour?

2. Experiment with soap bubbles or a fine coat of oil (vegetable oil) on a water surface. Do you get a spectrum of colour?

3. Experiment with coloured glass. Do the results change? If you can get bits of coloured glass from someone who does stained glass work, experiment with how different colours affect the spectrum of light. What happens if you use two colours of glass at one time? [Even the plastic overhead mathematics manipulatives will allow for experimentation with colour and light.]

4. Extend this activity into art and experiment with the mixing of colours of paint. Start with primary colours--red, yellow and blue. Mix pairs of these colours. Record results. Experiment with shades of colour by using more of one colour and less of another; and make use of white and black to lighten and darken shades of colours. Encourage discussion and sharing. Record findings.

5. Sky colours during the day, at sunrise and sunset, depend on particles in the air and the distance light is travelling. Try this experiment. Measure a cup of water (250 ml) into a clear glass. Use a flashlight in a slightly darkened room to shine light from the side, behind, etc. onto the glass. Now stir into the water a quarter teaspoon of milk to simulate pollution and dust particles in the air. Again use the flashlight to shine a beam of light from the side, back, etc. What do you observe? Discuss and record. (From the side the milk particles should scatter the blue part of the light; from the back the orange and pink colours should be scattered. When the sun is close we see blue skies; when it is further away we get coloured sunrises and sunsets.) This activity is adapted from Primary Science by Hartman, 1994.

1. Try to enjoy the delights of a kaleidoscope with simple materials. Use pattern blocks as manipulatives. Set up two mirrors so they sit at 90 degrees to one another. Tape the edge where they meet. A bit of plasticine will help hold them upright as you work with pattern blocks. Working within this angle formed by the two mirrors move pattern blocks to create interesting patterns.

2. For more sophistication try this idea adapted from Journeys In Science, Grade 4. Form into a triangle two square mirrors facing inward and a piece of cardboard of the same size. Tape together. Over one end of this triangle tape a piece of wax paper. Place a small aquarium with clear sides on its side. Place a small light inside. Place pieces of coloured plastic (overhead manipulatives work well) above the light on the aquarium. Holding your triangle a few cm above the aquarium look through the triangle. Move the plastic pieces around to change the pattern.