##### 3rd Grade Science Unit 2: Light and Sound

GLCEs:

P.EN.03.11 Identify light and sound as forms of energy.

P.PM.03.51 Demonstrate how some materials are heated more than others by light that shines on them.

A common misconception at this age is that while light is reflected by mirrors, it remains on other objects

Students need to see:

Light energy can be converted to heat or thermal energy when certain materials absorb it. Some materials are heated more than others by light that shines on them.

Dark materials absorb more of the visible spectrum of light. The absorbed light energy is converted and is released as heat energy. Since more of the spectrum is absorbed there is more energy that is converted to heat. Light colored materials absorb less and reflect more of the light spectrum (less energy) so less energy is released as heat.

Vocabulary:

light source

forms of energy

thermometer

degrees Celsius

light absorption

light reflection

Colored Sand and soil, colored papers, hats?

Thermometer to see relative differences (emphasis on warmer and cooler)

Materials:
1. a thermometer (preferably an indoor/outdoor thermometer because they have the largest temperature range)
2. a 1’ x 1’ piece of heavy corrugated cardboard
4. a clock
5. sunlight (If you’re short on sunlight, use a with a halogen floodlight, at least 100 watts. A halogen bulb is a good choice because it has a high light intensity and its light spectrum is very similar to sunlight.)
6. six pieces of construction paper ) in white, red, black, green, violet, etc

Procedure:
A simple way to measure how much light energy is changed to heat energy by measuring the changes in its temperature:

1. Separate the children into small groups

2. Have the children cut 2 inch squares of approx. six colored paper squares. Make sure each group has the same colors.

3. Have the children predict which colors will reflect the most light and which colors will change the most light into heat energy. Have the students use crayons to record their results on their lab sheet.

4. The children should lay their colored papers on a piece of cardboard and let it rest under a light source (sun or flood light). Make certain that all of the papers are exposed to the same amount of light. (see below)

5. If using a lamp, set the lamp so the bulb is 2 feet away from and perpendicular to the cardboard. Turn the lamp on.

6. Wait 30 minutes, and thenhave the children use their hands or cheeks to organize the papers form least to greatest temperatures.

7. Have the children use crayons to record their results on their lab sheet.

8. As a class, see if all of the groups agree with the order.

9. Discuss results.

Student experiences should include multiple opportunities to use light bulbs and sunlight to heat a variety of materials including light colored sand vs. soil, light colored paper vs. dark paper, light colored hat vs. dark hat.

Extension:

The instructor will demonstrate to children that other substances such as sand and soil will also convert light energy to heat energy.

Materials:

2 or more paper plates

Drysand, Dry soil(s) to fill each of the plates

Source of light

1. Fill the plates to the same depth with the dry soil or sand. Do the same with the rest of the plates. Lay a thermometer on each of the substances.

2. Allow the plates, soil/sand and thermometer to rest in the sun source.

3. Have the children predict which will reflect the most light and which substance will change the most light into heat energy. Compare the readings on the different thermometers. Then discuss the results.

The darker, drysoilshould absorb more heat. If the substance is wet, the evaporation taking place will cool it as will as any other substance.

As another extension, have the children bring in hats to school. They can then predict which hats will change the most light energy to heat energy and which will reflect the most light. Have the children touch the hats and put them in order for coolest to warmest. This should lead to a discussion of wise clothing choices for a sunny day.

White and light are the cooler colors on a hot sunny day. Dark and black will warm us on a cool sunny day.