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4F Motion #1
Light from the sun is made up of a mixture of many different colors of light, even though to the eye the light looks almost white....
4F Motion #5
Human eyes respond to only a narrow range of wavelengths of electromagnetic radiation visible light....
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12C Manipulation and Observation #3
Read analog and digital meters on instruments used to make direct measurements of length, volume, weight, elapsed time, rates, and temperature, and choose appropriate units for reporting various magnitudes....
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Sensing the Invisible: The Herschel Experiment
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Purpose
To reproduce William Herschel’s original experiment of 1800 that discovered the existence of infrared radiation.
Context
This lesson was developed by the Challenger Center as part of NASA's MESSENGER Mission, of which Science NetLinks is a partner.
In this lesson, students find out that there is radiation other than visible light being emitted from the sun. They reproduce a version of William Herschel's experiment of 1800 that discovered the existence of infrared radiation. This involves creating a device in which sunlight will pass through a prism and produce a spectrum of light on the bottom of a cardboard box. Using a series of thermometers, students measure temperatures at various locations within and outside of the spectrum. By doing so, students should come up with results that are similar to Herschel's and discover the existence of radiation beyond the spectrum of visible light.
The process of conducting the experiment and placing it in the historical context illustrates how scientific discoveries are often made via creative thinking, careful design of the experiment, and adaptation of the experiment to accommodate unexpected results. Students close the lesson by discussing current uses of infrared radiation and learn that it is both very beneficial and a major concern for planetary explorations such as the MESSENGER mission to Mercury.
Refer to the Science Overview section of the lesson for a summary of the science content relevant to the activities in the lesson. In order to successfully complete this activity, students should already have had some basic instruction in heat and energy transformations. Refer to the Lesson Overview for a more detailed explanation of what students will learn from the lesson.
Research shows that some middle-school students who have not received any systematic instruction about light tend to identify light with its source (e.g., light is in the bulb) or its effects (e.g., patch of light). They do not have a notion of light as something that travels from one place to another. As a result, these students have difficulties explaining the direction and formation of shadows, and the reflection of light by objects. Middle-school students often accept that mirrors reflect light but, at least in some situations, reject the idea that ordinary objects reflect light. Many middle-school students do not believe that their eyes receive light when they look at an object. Students' conceptions of vision vary from the notion that light fills space ("the room is full of light") and the eye "sees" without anything linking it to the object to the idea that light illuminates surfaces that we can see by the action of our eyes on them. The conception that the eye sees without anything linking it to the object persists after traditional instruction in optics; however, some 5th-graders can understand seeing as "detecting" reflected light after specially designed instruction. (Benchmarks for Science Literacy, pp. 338-339.)
Another fact worth noting is that without formal schooling, young people learn that many other kinds of waves exist: radio waves, X rays, radar, microwaves, sound waves, ultraviolet radiation, and more. But they still might not know what these things are, how they relate to one another, what they have to do with motion, or in what sense such waves are waves. (Benchmarks for Science Literacy, p. 88.)
As students construct their devices in this lesson, keep in mind that middle-school students who can use measuring instruments and procedures when asked to do so often do not use this ability while performing an investigation. Typically, a student asked to undertake an investigation and given a set of equipment that includes measuring instruments will make a qualitative comparison even though she might be competent to use the instruments in a different context. It appears students often know how to take measurements but not of what or when. (Benchmarks for Science Literacy, p. 360.)
Ideas in this lesson are also related to concepts found in the following benchmarks:
- 1B The Nature of Science: Scientific Inquiry (6–8) #1, 4
Planning Ahead
Materials:
Note: Parts of this lesson were extracted from the unit,
Staying Cool.
Motivation
Have students participate in the activities in the Warm-Up and Pre-Assessment section of the lesson. Students will find out what they already know about sunlight, rainbows, and spectrums and learn how light—when it passes through water droplets or prisms—breaks (or bends) into separate colors of varying wavelengths.
Using a scientific process that will prepare them to replicate Herschel's experiment, students will also be asked to consider how they would test for any differences in the colors they see when sunlight passes through a prism; be introduced to the idea of measuring temperatures in different parts of a spectrum to see if sunlight has an effect; and form a hypothesis or prediction about what will happen to each of the thermometers they use in the experiment scenario.
Development
As noted in the Procedures section, groups of three will be asked to set up the experiment, where they create and test a device to measure different parts (colors) of the spectrum of sunlight.
The Herschel Experiment student sheet will need to be followed to ensure the experiment is set up and conducted under the ideal conditions. Results will need to be recorded on page 4 of their student sheets. (An Answer Key has been provided.)
When finished, the results of the measurements from all groups will need to be compiled on a chart like the one in the Discussion and Reflection section. Students should be guided to the conclusion that infrared radiation is the "invisible light" that is being emitted from the sun that is just beyond the red part of their spectrums. Among the other activities in this section, students will learn about Hershel's extraordinary discovery of infrared radiation in 1800, other invisible forms of light, and the MESSENGER mission to Mercury and why infrared radiation is an important area for the designers of the spacecraft. (The MESSENGER Information Sheet will be needed for this latter activity.)
Assessment
Have students take part in the Closing Discussion, where they are reminded of the different forms of radiation that are emitted from the sun, and all the various ways that infrared radiation is used today (e.g., the MESSENGER mission).
As noted in the Assessment section, page 4 of the student worksheet may be used to evaluate student understanding of the lesson. This section features a number of extended activity ideas—like essays, reports, and posters—that students can do to enhance and reinforce what they have learned.
Extensions
For related Science NetLinks lessons, see:
Have students choose an application where infrared radiation is used and write an essay about it.
Infrared satellites have provided a lot of information about environmental changes on earth. Have students explore the NASA Earth Observatory website and discover how various parts of the electromagnetic spectrum are used in earth science observations.
Created :10/29/2004
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