Infrared Experiments - 1 of 4
This is a two-part exhibit. In one part, visitors can look at themselves using an infrared (IR) camera. In the other, visitors can experiment with heating a variety of objects in a variety of ways, and view the results with an infrared camera. In both situations the camera detects infrared light, which has a longer wavelength and less energy per given photon than light that is visible to the human eye. Just as flames get so hot that they give off light, your body, or the objects on the exhibit table, also get warm and give off light. Its just that they don't get hot enough to give off visible light. They are only warm enough to give off infrared light (which has less energy per photon than visible light). It is this light that is picked up by the IR camera, and translated into colors on the TV screen. Different screen colors correspond to different temperatures, so visitors will be able to use the infrared camera as a visual thermometer. They will also be able to experiment with the infrared light itself to discover that it works just like any other kind of light.
Main Teaching Points
Infrared light, though invisible to the human eye, is a type of light. It can be reflected, refracted, filtered, blocked, and focused. In every respect it works just like any other kind of light. Infrared light is primarily given off by objects around room temperature (~25° C). Hotter objects (~3000° C) will emit a bit more IR light, but will emit most of their energy in the visible spectrum. Cold objects (~ -250° C) will emit significantly less IR light and will emit most of their energy in the radio part of the spectrum. Special cameras can be used to detect infrared light and translate it into colors for the TV screen. Scientists can use images photographed in the infrared region to detect patterns that would otherwise be invisible to see. This is a very important technique in astronomy as well as in studying the Earth from space.
Research has shown that for a person to really understand something, he or she has to make sense of it for him- or herself. Simply hearing the “fact” that X-rays or radio waves are a form of light doesn’t mean that a person will really understand it. By way of analogy, how many times have you heard the statement that when stock prices go down, bond prices go up? If you don’t really have a good mental picture of how stocks work, how bonds
Infrared Experiments - 2 of 4 work, and how they interact with each other, then that statement is just a bunch of words. In fact, it is quite possible for you to spend an hour with your stockbroker and leave just as confused as when you started, because you didn’t have a good mental framework on which to assimilate all of the information he or she was giving you. It is literally true that without a framework to hang new information on, it is almost impossible to remember it and understand it. At this exhibit, visitors have the opportunity to construct mental models of heating, cooling, and infrared light for themselves. This act of constructing for themselves is essential to understanding. No matter how much information you give them, it won’t be enough. The best strategy is to give visitors suggestions of things to try, and to talk to them about their mental theories of what is happening. Then, after listening to their theories, suggest other things to try that will help them refine their theories. This exhibit also allows visitors to generalize concrete ideas from specific examples into abstract concepts. For example, “transparent” usually means you can see through something, and “opaque” means that you can’t. However, there are materials that are transparent when viewed with visible light and opaque when viewed with infrared. In other words, transparent and opaque are not merely properties of a material, but properties of a material and the wavelength of light you are using. This allows visitors to think about transparency and opaqueness in a new, more abstract way.
Suggested things to try
Try this: Put black and white blocks out on the table. Heat them with the blower and look at the pattern in the IR camera. Now, do the same experiment but heat them with the heat lamp. Why is the pattern different? Use the dull metal block to act as an infrared mirror. Heat the metal block with a heat lamp and watch the changing temperature patterns with the IR camera. Is metal a better heat insulator than wood? What materials hold their heat the longest?
Questions and Answers
Where does infrared fit into the full electromagnetic spectrum? Radio Waves Mircrowaves Infrared Visible Ultraviolet X-Rays Gamma Rays
Infrared Experiments - 3 of 4 Lowest energy (longest wavelength) Highest energy (shortest wavelength) Why does heating black and white blocks with the blower cause a different heating pattern than heating with the heat lamp? When you heat something, you are making its molecules move faster. If you heat blocks with the blower, hot (fast-moving) molecules in the air literally bump into the molecules in the block and cause them to move faster. This process is called CONVECTION. The color of the blocks makes no difference. On the other hand, when you heat the blocks with the heat lamp (RADIATION), energy from the heat lamp’s light is absorbed by the blocks and is converted into heat. Now the colors of the blocks make a big difference because the white blocks reflect most of the heat lamp’s light away and only a little is absorbed to heat the block. The black blocks absorb most of the light, so there is that much more light which the blocks can convert to heat. Demo: Do the above experiment with actual blocks. Show the convection, conduction, and radiation animations (on your laptop). What do you think will happen if you heat the blocks with conduction? Why are some materials transparent to visible light but opaque to infrared? Are there any which are opaque to visible light but transparent to infrared? First of all, it is important to realize that this is really not so strange. For example, think about a red filter – e.g. a piece of clear red plastic. This filter allows red light to pass through it, but not other colors, like blue light. (There are excellent filters on the Gas Tube Spectroscopy Cart to demonstrate this.) This red filter is transparent for red light and opaque for blue light. It is not unusual for a material to be transparent for some wavelengths of light but opaque for others. The soft tissue in your body is transparent to x-rays, but opaque to visible light. Glass is transparent to visible light, but opaque to infrared light. Why is this? Every substance is made up of atoms and molecules. Each type of atom or molecule can absorb certain specific frequencies of light. (These particular frequencies are the same as the frequencies of light you can observe with the Gas Tube Spectroscopy activity.) This process is very similar to how a crystal goblet will vibrate when an specific musical pitch is sounded. When you play a sound at the correct resonant frequency, the goblet vibrates and converts some of the sound energy into vibrational energy. A different-pitched sound hardly interacts with the goblet at all. The same is true of light. Light of the correct color can be absorbed by the molecules of a substance. The substance then looks opaque for that color of light. Light of other colors hardly interacts with the molecules at all and passes right through. The substance is transparent for those colors.
Other Cool Stuff to Try
What parts of your body are hottest or coolest? Can you write with heat?
Be sure that visitors use the equipment safely. While every effort has been made to make the equipment as safe as possible, an extra measure of caution is always wise.
Infrared Experiments - 4 of 4
The experiment table will probably need straightening up from time to time.
Background materials (websites, videos, articles, digital collections links)
http://www.ipac.caltech.edu/Outreach/Edu – All about infrared astronomy http://imagers.gsfc.nasa.gov/ems/infrared.html – NASA site explaining infrared, including cool pictures and links to other parts of the electromagnetic spectrum
Self assessment suggestions
After facilitating the INFRARED EXPERIMENTS several times, complete the checklist below, then highlight the box in the rubric that best describes your performance. Have your Guide Captain observe your demo then complete an identical rubric. Discuss your presentation technique with your Guide Captain along the lines of the rubric. A. Checklist of pre-requisite skills for facilitating INFRARED EXPERIMENTS 1. Knows where all materials and props are stored for experiments 2. Understands and can explain clearly the main teaching points of infrared energy 3. Can use the materials effectively to engage visitors and guide them to constructive "messing around"
B. Rubric for INFRARED EXPERIMENTS QUALITY LEVELS TRAITS Enthusiasm/fun Sparks visitors’ curiosity
Takes a pleasant tone and demeanor Directs visitor to digital collection or to other staff with more knowledge Tells visitor what to do step by step
Demonstrates a strong interest in SO experience
Knowledge of exhibit’s tools and props
Exhibits thorough knowledge of all parts of this demo
Animated, with good vocal inflection. Encourages explorations and fun Asks stimulating questions Understands content and to engage the visitor at explains on appropriate heightened level level. Opens news subjects for inquiry Asks visitors leading Coaches visitors by questions about what they encouraging them to expect to happen observe, hypothesize, and test their hypotheses Exhibits thorough Beyond thorough knowledge of all parts and knowledge, discovers new begins to innovate the use of ways to use these materials them for extended inquiry