What Other Type of Energy Accompanies Light from the Sun?

Materials Needed
• Magnifying glasses
• One sheet of paper per small group
• Glass bowls
Procedure
1. You will need to be in bright sunlight with no wind for this experiment.
2. Put the piece of paper in the bowl.
3. Hold the magnifying glass between the paper and the sun so a beam of light focuses on the paper.
4. Notice that as you move the magnifying glass closer toward and farther from the paper, the point of light changes in size. Notice also that it gets brighter as it gets smaller.
5. Adjust the distance between the paper and the magnifying glass to make the point of light very small and bright.
6. Pull the magnifying glass back about 1 cm (1/2 in.) and watch the paper.
7. Do you see anything happening to the paper? If so, what, and why do you think it is happening? What kind of energy is causing this to happen? Discuss your observations and ideas with your group.

Teacher Information
As light rays from the sun are concentrated by a magnifying glass, so are the infrared, or heat, rays. The magnifying glass can concentrate bright sunlight to such a degree that it will scorch the paper or even possibly ignite it. The focal distance for heat (infrared) rays is slightly longer than the focal distance for light. For this reason, students are instructed to move the lens back slightly after the focal point of light is found. They will need to adjust the distance from lens to paper slightly to find the focal point for heat- the point at which the greatest possible concentration of heat is focused on the paper.

Science Process Skills
Observing, inferring, classifying, measuring, predicting, communicating, using space-time relationships, formulating hypotheses, identifying controlling variables, experimenting