# 46. LET IT SHINE

from Come Fly With Me – Exploring Science through aviation and aerospace concepts.

SUBJECT: Science
GROUP SIZE: Large or Small
TIME: 60 minutes
TYPE OF ACTIVITY: Student Investigation or Teacher Demo
TEACHING STRATEGY: Guided Discovery Expository
SKILLS: Observation Inference Collecting Data
Objectives: To distinguish between the presence and absence of solar energy by means of a radiometer; to observe and describe the effects of low and high amounts of solar energy on a radiometer; to demonstrate that solar radiation can do work.

Materials: Paddle type radiometer (at least one or as many as one for every two students); squares of different material 30cm on a side (black paper, cardboard, cellophane in several colors); can or oatmeal container large enough to fit over the radiometer.
Teacher Background Information:

The atmosphere inside a radiometer is a partial vacuum. With many of the molecules of air removed from inside the globe, those left can move about much more freely than those outside the radiometer. Each paddle inside the radiometer has a dark and a light colored side. The dark side of the paddle absorbs more heat energy than the light side. As molecules of air strike the dark side they pick up much more energy than those striking the light side. The result is that the molecules kick away from the dark side and cause a reaction in the opposite direction propelling the paddles. Check online for additional information.
Procedure:

1. Have the students examine the radiometer for several minutes before you begin.
2. Place the radiometer on a desk or table in the sunlight and have the students observe and record what happens.
3. Place different squares of material in front of the radiometer and record the observations again.
4. Place a container over the radiometer and remove it after several minutes. Record what you observe about the radiometer immediately after it was uncovered.

What happened when the radiometer was placed in the sun? When it was shaded with different materials? When it was covered? In which direction did the paddles spin? How does the radiometer detect solar energy? How does the radiometer demonstrate that sunlight can do work?
Extensions:

Use a light source like a slide projector and shine the light at different angles on the radiometer. Record the rotation rate of the radiometer at different angles. Relate this to the angle of the sun at different times of the year in relationship to the earth. At what angle was the rotation rate the greatest? The slowest?

At what angle, in your area, would it be best to place a solar collector in relationship to the sun? At what time of the year would your collector be the most efficient? If you were going to use solar collectors on a space vehicle (for electricity or propulsion), what provisions for the relationship of the collectors to the sun would you make? Could you use the solar energy demonstrated by the radiometer to propel a space vehicle? Why or why not?
Adapted from Dept. of Energy, CS-0062, SOLAR ENERGY PROJECT ACTIVITIES, JR. HIGH SCIENCE

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