Absorption and Reflection

This activity will demonstrate that radiation from the Sun (sunlight) can be converted to heat energy by absorption, and also that solar radiation can also be reflected.

Time requirement: 50 minutes as an activity, 20 minutes as a demonstration.



  1. Wrap each paper cup with a different color paper. Tape the paper to the cups if necessary. Make a lid for each cup with the same color paper as the cup.
  2. Poke a hole in each lid the same size as the thermometer. Make sure that the thermometer will fit snugly in the hole.
  3. Place each cup in direct sunlight and insert the thermometers through each lid.
  4. Observe the temperature of each thermometer while keeping an eye on the clock.

Observation questions

  1. What was the beginning temperature for each cup?
  2. How long did it take before the temperature in at least one of the cups began to rise?
  3. How long did it take for the hottest cup to reach its maximum temperature?
  4. What was the difference in temperature of the two cups after the temperatures of the cups stabilized?
  5. Why did the cup(s) heat up?
  6. Why would one cup have a higher temperature inside?
  7. Do cars with dark interiors heat up more than cars with light interiors when they are in direct sunlight? Why???

Last updated: September 02, 1997
Joe Twicken / joe@nova.stanford.edu
Rob Wigand