Beyond the Visible
Activity 1D: Heat Sensitive Paper
Please note: Patty Miller demonstrates this activity on-camera during Science in the Stratosphere
To use heat-detecting papers to reinforce the concept that radiation that's invisible can still be "visualized" by the appropriate detectors.
Ask students to identify something which changes color when exposed to sunlight. Students may think of carpets, blinds, photographs and a wide variety of other things that sunlight bleaches.
Explain that there are special dyes which react relatively quickly to heat. The paper which you can distribute to students (4 sheets of paper and one sheet of heavier card are included with the mini-kit) is tinted with such dyes. These sheets are re-usable: simply move them away from the heat source and they will regain their original appearance. You can find out how to order in bulk from the supplier, Educational Innovations, in our Multimedia Resources section, page 61.
Please note: when your students hands are in contact with the paper, heat is being transferred through conduction, not radiation: the KAO detects heat radiating from a distance.
Procedure Distribute the pieces of heat-sensitive paper, perhaps with the page from the Guide copied over to it, or with a separate copy of the activity sheet. (Yes, the copier will make darker colors turn white, but don' worry: they'll soon cool down and be ready to use!) Read over the activities on the sheet. Allow students working in groups of 2 or 3 to try the first experiment, (Hand Heat), and record their observations.
For the second activity, students will need heat lamps or a sunny day. The time required for the paper to change color depends on the intensity of the light source. Check in advance about going outside: if the day is too hot, the paper will change color all over, simply by being exposed to sunlight.
Ask students to make a list of objects that produce heat. Experiment with holding the paper at different distances from these objects. A heat image is called a thermogram. An example (the man holding the match) appears in the Science in the Stratosphere video.
Fax paper is a thermal image. Fax paper exposed to a hot object, will darken. Encourage students to explore other uses for thermal images in printing and medicine.
One of the first to experiment with the spectrum was the English mathematician and physicist, Sir Isaac Newton. He placed a thermometer in a part of the spectrum where there was no visible light, but where he detected an increase in temperature. The activity suggested here echoes that famous precursor. Encourage students to research Newton's other work with light and the spectrum, and suggest other parallels with the LFS activities.
NASA's Space Based Astronomy book contains a very useful demonstration of how energy and wavelength are related. See page 43.
Suggest that students keep a Journal of their work on LFS, and record the results of their hands-on activities. Ask them to relate what they do in class to the activities they see aboard the KAO during the videos. Encourage them to go on-line and use the Researcher Question and Answer pairs, Field Journals and other resources. Ask them to make as many interdisciplinary connections as possible--and report on what they find most interesting about the project.
Heat Sensitive Paper
Warm objects give off infrared radiation. Try these experiments with a special paper that reacts to heat.
Touch the heat sensitive paper with your thumb while the paper is (1) in the air, (2) on a metal desk or cabinet, (3) on a stack of papers, and (4) between your thumb and finger. Does the "background" make a difference in the results?
With a thick black marker, draw the shape of a galaxy with spiral arms, or a planet with a banded atmosphere, on a piece of white paper. Place the paper on top of the heat-sensitive paper and put both outside, or under a heat lamp. Peek under the paper after 20-30 seconds. Continuing exposing until you see an image appear. Compare the parts of your drawing which reflect light with the parts that absorb light and convert it to heat.
Use the heat-sensitive paper to find heat sources. Try the following objects and then do your own detective work:
1. heater: How far away can you be and still detect the heat radiation?
2. copier: What happens to the paper when you run it through a copier? How long until the color returns?
3. breath: Breathe on the paper. Be careful not to touch the paper with your lips. Do some people produce hotter air than others?
Place different colored pieces of construction paper on top of the paper. Choose light colors and dark colors. Place the paper under a heat lamp or out in the sunshine. After a few minutes, look under the different colored sheets. The energy in the light striking each sheet of paper is reflected away or absorbed and turned into heat. Which colors are radiating more heat.?
Warm objects produce infrared radiation, which the KAO detectors can
picks up. The heat-sensitive paper detects the warm objects directly when
you put your hand on it: it's not reacting to infrared. A microwave oven
produces radiation similar to infrared radiation. Water molecules absorb
this radiation and warm up the food they are in. Does heat-sensitive paper
react more to a heater or to a microwave oven?