Heat Camera

The image of a person in far infrared radiation.

Introduction

Far Infrared radiation can be explored with a thermal imaging camera.

Material

A camera that makes images in the far infrared, science museums often have these, also you can contact your electric or gas company to see if they will come to the school with one, they use them to analyze energy leaks in homes. There may be other energy conservation groups in your town that have thermal imaging cameras.

To Do and Notice

Stand in front of the camera and look at your image on a television screen.

The image may be color or black and white. If it is in color it is called false color.

Looking at your body, what do you think the colors (or the brightness of the black and white) represent?

If you have several companions shake hands with them and find out who has the coldest hands and who has the warmest hands. (See the exploration Hot Hands) Then have these people hold their hands up in front of the camera. Notice that the image of the person with the hot hands has bright hands, while the image of the person with the cold hands has darker hands. The camera image shows the brightness of infrared radiation, and hot objects are brighter in the far infrared than cold objects.

Look at parts of your face, notice which parts are bright and which parts are dimmer. Feel the different parts with your hand to see if you can detect the temperature differences.

Look at your lips. Inhale with your lipps nearly closed. Notice how your lips darken as they cool. Then exhale and watch them brighten as they warm.

If there is a piece of room temperature metal around press it against your flesh for 15 secconds. When you remove the metal you will have an infrared tattoo in the shape of the piece of metal where the metal has cooled your skin.

What's Going On?

The thermal camera detects infrared radiation emitted by an object. More intense infrared radiation is displayed on an image as brighter light.

When you see your image in visible light the light comes from a source such as a lamp or the sun and reflects off of you, however you are the source of the far infrared radiation displayed in the image produced by the thermal camera. If the room lights are turned off your image in the thermal camera will be just as bright.

The intensity of the infrared radiation increases as the temperature of the object increases. The thermal imaging camera shows an image of the temperature distribution of an object.

So What?

Pit vipers such as rattlesnakes have two facial pits that can not only detect far infrared radiation, each can make a pinhole image using infrared radiation. Since there are two pits one on each side of the face, the brain of the viper can create a three dimensional image of the world in infrared radiation. Warm blooded creatures such as mice can be detected by the pits of the pit viper allowing the snake to strike at the mouse, poison it, and eat it in complete darkness.

Energy conservation groups can take a thermal image of a house and detect where the exterior of the house is hottest. The homeowner can then work to reduce heat loss in these areas saving energy and money.

Going Further

Clear plastic is opaque in the infrared

Find a piece of thick clear plastic such as a clear plastic jewel case for a compact disk.

Look at the plastic with the infrared camera, notice that the plastic is clear to visible light and opaque to infrared light. The plastic is cool in the infrared, room temperature so it does not emit much infrared radiation and in fact absorbs infrared radiation from its surroundings.

Black plastic bags can be clear in the infrared

A thin black plastic trashbag is opaque in visible light, however if the bag is thin enough the thermal imaging camera can see through the bag. The thickness of the bag is thin when compared to the wavelength of far infrared radiation. The infrared radiation does not interact with the black plastic as much as visible light. The thickness of the bag is tens of times the wavelength of visible light.

Metal Mirror

Find a scratched piece of copper or aluminum metal, like the bottom of a copper covered frypan.

Use the piece of metal as a mirror. It does not make an image in visible light. However, it does make an image with far infrared radiation. The scratches in the surface of the metal are much larger than a wavelength of visible light and so scatter it in all directions, the scratches in the metal are smaller than a wavelength of far infrared so the metal reflects the infrared without scattering it.

 Scientific Explorations with Paul Doherty © 2005 18 August 2005