ACTIVE PARTICIPATION:

1. Let students work in small groups. Give each group two jars the same size (or use glasses or beakers). Fill one with hot water and the other with cold water. Place 4 drops of food coloring into each jar of water. Do not disturb the jar. Have the group observe what happens. (The food coloring will spread more rapidly through the hot water.)

2. Student activities on radiant energy.

A. (Let students work in small groups. Give each group a magnifying glass and tissue paper. Go outside and with the magnifying glass focus the rays of the sun on a bit of tissue paper. Observe what happens. (The concentrated rays of the sun will make the paper smolder.) Ask students to blow gently on the paper and observe the effects. (The paper may burn.)

B. Have students take 2 jars or bottles the same size. Put black construction paper around one. Fill both with water. Take the temperature of the water in each bottle. Record. Now put both jars of water in a window in direct sunlight. After thirty minutes, take the temperature of the water. Record. Which bottle absorbed more radiant energy? (The one with the construction paper.) Why? (Because radiant energy is absorbed and caused the molecules of water to become warmer and move faster.)

C. Place an electric light bulb on a table. Turn it on. Have students hold different materials near the bulb but not touching it. (Use cardboard, glass, cloth, paper, etc.) Observe which materials get warmer and which get warmer more quickly. Place several thermometers on the table at different distances from the bulb. Have students record the distance and the temperature on that thermometer. Record the temperature again after 5 minutes, 10 minutes, and l5 minutes.

3. The candle can be used to experiment with heat.
A. You should closely watch students as they do this activity. Have a student hold a paper plate over a candle flame. (It will quickly catch fire so have a pan of water close to dose the flame.) Now soak a paper plate in water and hold the wet plate over the flame. Observe the difference. (It will not burn at first; the heat is absorbed by the water but after the water has been boiled away the paper will reach its kindling temperature and burn.)

B. Stick a lighted candle to an aluminum pie plate. Put a glass chimney over it but have it rest on two pencils so it is not touching the pie plate. Observe. (The candle burns freely because air is readily available.) Now remove the two pencils and let the chimney rest on the pie plate. Observe the candle. (The flame flickers and smokes.) Now put a piece of glass on top of the chimney. Observe. (The flame goes out.) What is your conclusion? (Air "oxygen" is necessary for most fires.)

4. Have a student drive a nail into a piece of wood and using a claw hammer, pull it out. Feel the nail. (It is warm.) Have a student take the temperature of a cup of sand. Record it. Now put the sand in a can, jar or cardboard tube and shake the sand back and forth for several minutes. Take the temperature of the sand again. Record it. What happened? (The temperature is higher because friction caused the sand particles to heat up.)

5. Have students construct a simple water calorimeter by getting a large tin can and a smaller tin can that will fit inside the larger one. Put some kind of insulating material along the bottom and sides of the larger can. Use newspaper or wool cloth or Styrofoam. Put the smaller can in the center and finish packing around the can with your insulation. Pour into the small can some water. Cover the two cans with a piece of wood into which you drill a small hole just large enough for a thermometer. Record the temperature of the water. Now have students heat an iron nail in a pan of boiling water and drop the hot nail (use tongs to pick it up) into the water in the calorimeter. Close the top quickly. Now record the temperature of the water. What happened? (There should be a rise in the temperature of the water as the iron nail cools.)

You have learned that heat is a form of kinetic energy, energy in motion. The more heat an object has, the more energy it possesses. On the sun, heat is produced by nuclear energy which is radiated through space in all directions. Heat is also produced by friction, or mechanical energy, chemical energy, and electrical energy. We have learned that temperature is not the same thing as heat and they are measured in different ways. Heat is measured by using a calorimeter and in units of either calories or British Thermal units. Everyday we use heat in different ways. We heat our homes, schools, offices, we cook our food and run our cars, ships, and planes.

This lesson addresses Instructional Objectives 2.12, 2.13, 2.14, 2.15, 2.16, 2.17, and 2.18 .

SKILLS:

Listening, observing, recording, inferring, communicating orally, comparing, contrasting, investigating, drawing conclusions

3 to 5 instructional periods

Kerosene lamp, a dozen candles, a variety of clear incandescent bulbs and fluorescent bulbs, 6-8 flashlights, 6-8 pieces of copper wire (each about 6 inches long), glass jar or beaker, water, white and black construction paper, box of aluminum foil, piece of cardboard, mirror, cloth, piece of glass (approximately 6 x 8 or larger), book, a clear prescription vial or small jar - one for each student, newspaper, 6-8 sheets of construction paper, light meter (if available).

Candle, fluorescent bulb, illumination, incandescent bulb, light, light meter, luminous, photon

(Turn off the lights in the room and close blinds or shades to make the room as dark as possible.) Man has always known the importance of light. Years ago he had to get most of his work done during the daylight hours. After sunset, man would have to read or work by the light from a fire or candles or lamps. Today we can practically turn night into day with the use of electricity. (Flip the switch and turn the lights on.)

As our ways of using light have improved, we have learned to do more and more activities at night. We have become so accustomed to having light that we take it for granted. But have you ever stopped to think about the importance of light? With light, scientists can see tiny germs that cause disease or distant stars and planets. Because of light you can take photographs, go to the movies or watch television. Today we are going to learn more about light and its importance to us.

When we studied heat we learned that all matter is made of atoms and these tiny particles have energy. An atom that gains energy is said to be excited. An excited atom must eventually give off this extra energy. An atom radiates the extra energy and we call this radiant energy. The radiant energy is released in a tiny bundle called a photon. Light, then, is a stream of photons given off by excited atoms. This energy can be seen. An atom can gain the extra energy in several ways: colliding with other atoms, heat, electricity. Some objects are luminous - they give off their own light. Luminous sources found in nature are the sun and other stars, fireflies, some plants, and certain deep-sea fish. Luminous sources of light which are artificial, or man-made, are incandescent bulbs, fluorescent bulbs, candles, kerosene lamps, etc. Most of the objects you see are non-luminous, they do not give off their own light. The only way you can see such objects is because they reflect light. (Have students do Activity One under Active Participation.)

Man has burned many substances for light. Early man probably used light from a burning stick. Then he found a pine knot would burn longer. He found if he dipped the pine knot in animal fat it would burn longer. His next step was to put the animal fat into a dish of some kind and, finally, he put a wick in the animal fat. Candles were made in a similar way, using wax instead of animal fat. Kerosene lamps were once widely used for home lighting. (Have students do Activity Two under Active Participation.)

All the early sources of light used an open flame. They were dangerous and a lot of trouble - keeping a supply of candles or kerosene on hand, trimming wicks, and there was soot and smoke. After we learned to make electricity, scientists began to experiment in using it as a source of light. One problem he had was finding a wire that would give off a bright light and another problem was making the wire burn a long time. Also the wire had to be covered. Thomas Edison made the first incandescent bulb, a glass bulb containing a filament in a vacuum or gas. His filament was a carbon thread. He removed the air from the bulb and passed an electric current through the carbon thread. The filament became hot and glowed. Today most bulbs use tungsten filaments; they give brighter light and they burn longer.

In a fluorescent bulb, electricity is passed through a tube filled with particles of mercury gas. These particles and the material used to coat the tube glow when electrons pass through the tube. These bulbs are cheaper to operate, stay cool, last longer and cause less glare. (Have students do Activity Three under Active Participation.)

One of the first things we want to measure when we measure light is its speed. You know that lightning and thunder occur at nearly the same time but you see the lightning first and then hear the thunder. So light travels faster than sound. Also you learned that sound cannot travel through a vacuum - it must travel through some matter. Light can travel through a vacuum; you can see light from the stars. Through space light travels at a speed of 186,000 miles per second. When you turn on a light the room is flooded with light all at once. Every corner is lighted up at the same time. Light can also travel through matter like air, glass, and water. However, matter slows down the speed of light. When it slows down it changes direction or bends. This bending is called refraction. (Have students do Activity Four under Active Participation.)

Another way we measure light is a unit called a candle. This measures the intensity of light. The amount of light being produced by a light source is compared with the light produced by a standard source. And because the first standard source was a candle, we call it candle, even though today the standard source is a light bulb of a certain candlepower. To measure the illumination at a given place we use an instrument called a light meter. Illumination is the amount of light falling on a certain surface a certain distance from the light source. The Law of Inverse Squares simply means that the greater the distance from the light source, the less light reaches you. If you move twice as far away from a light bulb, only one-fourth as much light falls on you. When the distance is increased three times, the light reaching you is one-ninth as much. When light shines on a light meter, a small electric current is generated. A meter measures the strength of the current. (Have students do Activity Five under Active Participation.)

Light is one form of energy we use almost constantly. Your ability to see depends on light. Light is important in other ways as well. Plants could not live without light. All living things depend on the food that plants make. Fossil fuels are formed from the remains of once living organisms that depended on light. Scientists have developed many instruments that use light. Light helps man learn about his world by using the microscope and telescope. Eyeglasses use lenses and the refraction of light to help us see better. We use a camera to record faces and scenes on film in photography, movies, and television. Magnifying glass lenses focus light rays and bring them to a point to make objects appear larger.

Laser light is a special kind of beam of light. Laser, or light amplification by stimulated emission of radiation, has light waves that are exactly the same wavelength. Laser light travels in one direction with little spreading so it is very intense and powerful. Its light is also very pure - it is made up of light waves of a single color. Laser beams are used in medicine to treat eye disorders in surgery, and to destroy diseased tissue. In industry laser beams can drill holes in machine parts or weld metal parts together.

In the future most telephone calls may be carried by light waves traveling through optical fibers. Thousands of calls Cs be carried at the same time by a beam of laser light. Many stores are using lasers in checkout lines. A Universal Produce Code is printed on each product. A laser beam is bounced off the bands of the code and a computer identifies the code. The computer figures the bill and keeps a record of what was sold. Holograms are three-dimensional photographs produced by lasers. We are finding more and more uses for light each year.

(Have in class a Kerosene lamp, electric lamp, candles, a variety of clear incandescent bulbs, fluorescent bulbs, flashlights.)

1. Have students work in small groups of 4 to 8. Give each group a candle and have them light it. Hold the candle near (not touching) a piece of white construction paper, a piece of black construction paper, a glass of water, smooth aluminum foil, crumpled aluminum foil, piece of cardboard, mirror, piece of cloth, clear glass, textbook. Record the results: which surface could you see the image of the candle? Which surface was rough and which was smooth? (They can pass the objects from group to group.) Conclusions: light reflects evenly off smooth surfaces and you can see an image in most smooth surfaces; light reflects off rough surface in all directions and no image can be seen.

2. Place a kerosene lamp on a table. Have a student remove the chimney and light the wick. Turn it down low and replace the chimney. Turn classroom lights off. Observe the color and brightness of the lamp. Place an electric lamp on the table and turn it on. Compare the light from both. Turn the wick up higher. What do you see forming on the inside of the chimney? (Soot)

3. Demonstrating incandescent and fluorescent bulbs:

A. Working in small groups, give each group a flashlight. Have them take it apart. Take a piece of copper wire about 6 inches long and wrap one end around the brass part of the bulb. Have a student hold the two dry cells end to end. Have another student hold the base of the bulb on one end of one of the dry cells. Touch the other end of the wire to the end of the other dry cell. Observe the bulb. (It lights up.) Explain what happened. (The batteries supply electric energy which passed along the wire to the filament in the bulb causing it to heat up and give off light.)

B. Give a student a fluorescent light bulb. Have him hold the bulb as he rubs his feet on a rug (If school does not have carpeting, have a square of carpet for this.) an electric charge by touching one end of the bulb to a metal object in the room. (Be sure room is dark for this.)

4. To demonstrate how speed of light changes when it passes from air into water or glass, give each student a clear prescription vial or use small jars. Have them fill their vial completely full of water and snap on the cap securely. Lay part of a newspaper on the desk. Lay the vial on the print. Try the vial side to side and then lay it top to bottom. Try raising the vial away from the print. Experiment with the water vial. Observation: As light passes from air into other matter it slows down and bends (refracts). Lenses use refraction to magnify an object or to make it appear smaller.

5. Demonstrating light intensity and illumination:

A. Have students work in small groups. Give each group a flashlight and a piece of poster board or construction paper. Prop the poster board against a wall. Have one student turn on the flashlight and stand one foot from the poster board with light focused on the center of the board. Have another student draw a square box around the area on the board where the light is most intense. Have the one holding the flashlight move back one foot and repeat the procedure. Do this until the beam of light covers the entire poster board. Have students compare how much light or how intense the light is that reaches the first square as the distance from the flashlight increases. Conclusion: the greater the distance from a light source, the less light reaches that square.

B. If you have a light meter available, have students compare the illumination in different places. (Be sure to include candle light, light from bulbs, sunlight, etc.)

You have learned that light is a visible form of radiant energy released as a stream of photons by excited atoms. The sun is still our most important source of light. With electricity we have electric lights that enable us to be more independent of daylight hours. It is almost impossible to say too much about the importance of light in our lives and every year scientists are finding new ways to use light. Plants, fuels, lenses in glasses and optical instruments, laser, and, most of all, our vision - all depend on light.

candle - unit for measuring the intensity of light

fluorescent bulb - an electric bulb consisting of a glass tube containing a gas or vapor which produces light when electric current is passed through it

illumination - the amount of light falling on an area or surface

incandescent bulb - a glass bulb containing filament in a vacuum; the filament glows when an electric current is passed through it

light - a visible form of radiant energy released by excited stream of photons

light meter - an instrument used to measure the illumination at a given place

luminous - giving off its own light

photon - a tiny bundle of energy released by an atom as it changes its energy state

pitch - the highness or lowness of sound

rarefaction - the part of a sound wave in which air particles are farther apart than they usually are

sonar - sound navigation and ranging

temperature - the average kinetic energy possessed by the molecules in a substance

ultrasonic - sound frequencies above 20,000 hertz

vibration - a quick back and forth movement

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Eighth Grade Science Home Page

Last Modified Wednesday, 13-Jul-2005 13:42:46 CDT