Infrared Energy

Resource for Grades 6-12

| Citation

Media Type:
Video

Running Time: 2m 43s
Size: 15.7 MB

This media asset was adapted from "Earth Science Week 2010 - Infrared Energy" NASA Goddard Space Flight Center.

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Related Resources:

The Electromagnetic Spectrum: NASA
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Infrared Gallery
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Tour of the Electromagnetic Spectrum: Infrared
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Electromagnetic energy travels in waves (electromagnetic waves) and spans a wide spectrum from long-wavelength/low-energy radio waves to short-wavelength/high-energy gamma rays. The electromagnetic spectrum is a continuum without any specific defined boundaries, but scientists have defined seven distinct regions. In order from low-to-high energy, those regions along the spectrum are: radio waves, microwaves, infrared waves, visible light, ultraviolet, x-rays, and gamma rays. Even though these areas have different names, all electromagnetic waves share similar characteristics and all travel at the same speed – the speed of light. In a vacuum, the speed of EM radiation is about 6 trillion miles per year, or about 9.5 quadrillion (10¹⁵) meters in one year.
Humans can see only a narrow band of the electromagnetic spectrum: visible light. Instruments like satellites, telescopes, cameras, and other devices expand our ability to perceive wavelengths beyond the visible range. A radio, for example, detects wavelengths correlated with the radio segment of the spectrum, while an x-ray machine detects electromagnetic waves from the x-ray segment of the spectrum. When EM radiation hits a sensor or detector, its energy gets transferred, so the detector can “see” and sense what kind of radiation it is. Since the energy of radiation is linked to wavelength and frequency, knowing the energy level of an incoming EM can tell you where it is on the spectrum and what its frequency is. Scientists use instruments and detectors “tuned” to wavelengths across the entire electromagnetic spectrum to study Earth and beyond. An example would be that some telescopes "see" visible light, some "see" x-rays, some “see” gamma rays, etc. In this video, you’ll see examples of sensors that “see” infrared energy.
Infrared energy is electromagnetic radiation with a longer wavelength (lower frequency) than visible light. Its name – “infrared” – means “below” or “beneath” red, referring to the fact that infrared radiation has slightly less energy than visible red light. Our eyes can’t see infrared waves – they aren’t “tuned” to infrared - but we can sense infrared energy as heat and instruments can detect and capture infrared waves, thereby allowing us to “see” thermal images of objects emitting infrared radiation. Night vision goggles, for example, detect infrared energy and “translate” temperature differences into visible wavelengths. Most of the energy coming from the Sun is infrared energy. (Most of the rest is visible light and ultraviolet energy.) Infrared energy is not the only kind that can cause materials to heat up. Since all wavelengths carry energy, all types of radiation can generate heat. Anytime electromagnetic radiation is emitted (by the Sun, a flame, a red hot nail) and then absorbed (by a plant leaf, a pot of water, or your skin), heat is transferred.

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Discussion Questions

Before Viewing

Fire is an example of something that gives off both light and heat. The Sun is another such example. Can you think of an object that gives off "invisible" heat - heat you can "feel" but can't "see?"
Do you give off heat? What's your evidence?
Think of a time when you saw an x-ray - yours or someone else's. What do you think the x-ray machine was "seeing" when it created the image?

While Viewing

What kinds of objects give off thermal energy?
On the electromagnetic spectrum, what is the relationship between infrared energy and visible light?
What are some of the things scientists study with infrared energy?
How did Sir William Herschel discover infrared energy?
Tip: Pause video at 00:35 and rewind to 00:19 to see the visible/infrared comparisons a second time. Pause again at 00:35 and ask students to share their observations about how the images compare.

After Viewing

In your own words, describe what infrared energy is.
How is infrared energy similar to energy from other parts of the electromagnetic spectrum – and how is it different?
Why are satellites able to capture infrared images of the Earth during both daytime and nighttime?
How do you think an infrared image of a fire in a fireplace would differ from the same scene viewed normally with your eyes?
Bonus question: What do you think a lizard might look like when viewed through a thermal imaging camera? Hint: Remember that lizards are cold-blooded, so a lizard’s body temperature changes based on its surrounding environment.

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Teaching Tips

Classroom Activity: Infrared Morse Code

Students send messages using the invisible infrared signals emitted by TV remotes.

Materials needed: several TV remotes, cell phones with cameras, and Morse Code charts.

Students begin by exploring the remotes and viewing their infrared signals through a cell phone camera. (Most cameras “see” in infrared as well as visible light.) Students work in teams of two, though if there aren’t enough supplies to support groups of two, the student groups can be larger.
The teacher comes up with a sentence for each group – or the same sentence for all groups – and shares it with the person in each group handling the remote. The second student stands facing the first student and views the remote through a cell phone camera. The first student begins transmitting the message based on its Morse code sequence.
Students work silently, with the first encoding the message into Morse code and transmitting it using the remote to trigger infrared signals while the second student, watching the remote through the cell phone camera, uses another Morse code chart to de-code the message and write it down. Afterward, the two students compare the sent and received messages.
This activity could be organized as a game or competition based on which team can accurately transmit the message in the least amount of time.

Discussion Questions:

If you look at the remote with just your eyes, you can’t see any energy transmissions. What does that tell you about the kind of energy being emitted by the remote?
Why do you think the cell phone cameras were able to “see” the infrared energy?
If you split visible light into its component colors and project a spectrum onto a wall, what kinds of tests might you do to confirm that infrared energy exists just beyond the range of visible light? What do you think your cell phone camera would “see” if you aimed it at this spectrum?

Note: For classrooms with access to an infrared camera or a web camera that has had its infrared filters removed, activities can include viewing a range of objects through the infrared set-up, comparing those images to visible light images, and/or creating infrared images as prompts for discussion and interpretation.

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Transcript

Rob: Any form of matter that we can think of having a temperature, no matter how hot or cold, gives off thermal energy.

A chair, a book, food, me.

Everything around us, even the Earth itself, radiates thermal energy. Thermal energy forms the primary source of what we call infrared radiation. Infrared being the section of the electromagnetic spectrum that is just beyond visible light in terms of wavelength size. We cannot see infrared radiation. In fact, humans can only see a very small portion of the electromagnetic spectrum, but technology allows to detect and image matter in this very important part of the spectrum. NASA, NOAA, and other agencies, use thermal infrared imagery to study Earth systems in a way beyond what we could ever see.

Through infrared data, we can study ocean and ice changes, map deforestation and forest fires, and monitor soil moisture and detect diseased vegetation. In fact, nearly every time we look at a weather report, from a heat wave to a hurricane, we are using thermal infrared imagery. Satellites detect infrared energy in a way that lets us study the Earth's weather patterns over both day and night, which is crucial for predicting the weather to come. In a way, it's as if the whole planet becomes visible to us at any time of day. Just over 200 years ago, Sir William Herschel discovered the existence of infrared by studying the sunlight passing through a simple prism. The prism separated all the colors that make up sunlight in an array called a spectrum.

Here's a simple classroom activity that lets us see the phenomenon Herschel first observed. Herschel measured the temperatures of the different colors and found that the temperatures increased as he measured from violet to red. But what really struck him was the observation just beyond the visible spectrum. First, measure the ambient temperature of the box by placing the thermometers in the shade. Once the prism is adjusted for the widest spectrum possible, place the thermometers in the blue, yellow, and in the area just beyond red. Measuring over time, we will see the temperatures increase as we approach this infrared section of the spectrum. It may seem like a big jump to go from a prism on a box to the advanced imagery satellites provide around the globe, but it all helps to explain how there is more to light and energy than meets the eye.