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MESSING ABOUT WITH INFRARED LIGHT William Beaty 2/24/95 I've always been fascinated with "heat radiation;" otherwise known as longwave in don't need a military night-vision camera, since there is an inexpensive imaging det crystal postcards. These postcards are available from several science supply catalo museum stores, also some mall gift shops, etc. If you heat the postcard until it just color, it becomes sensitive to small amounts of IR light, and acts like instant camer to try: Shine a hot (100 watt) light bulb on the IR postcard, and make a shadow wit thermal shadow appears on the postcard. Still shining the light, hold a piece o your hand so your hand and the glass cast a shadow. Although the shadow of invisible (except for the edge), the color-thermal shadow indicates an opaque is transparent to visible, but acts "black" to long IR. The opposite of the above demo can be performed with black plastic IR filter black material is held up to cast a shadow, the colored thermal shadow will n (except for maybe the edge of the filter). Deep blue filter plastic will do this, better when held together with a red filter to create visible-black, but IR trans Fully-exposed B&W film negatives also act like IR filters, as also do the silic available from some science suppliers. Glass isn't totally opaque to long IR, so it is possible to use a lens to focus a postcard. The hotspot is actually an image of the lightbulb. Try doing the sa electric heater! And try doing the same with the lens covered with one of the above. Also, I think acrylic lenses and acrylic fresnel lenses might work even polyethelene fresnel lenses used on motion sensors for security lights. I've never tried it, but it MIGHT be possible to pre-heat the postcard, then us cast the IR image of the view outside a window onto the card, so for a mome see an IR image of the world.


Use an ice cold cola can to make a cold ring-pattern on your arm, then quickl postcard against your arm. The cold ring becomes visible. Look closely and y see veins and arteries for a moment as the LC postcard colors pass through t sensitive range. Cool some pennies, and heat some others in your hand. Scatter them on the then move them a bit. Some have colored shadows behind them, others do n some drops of hot and cold water onto the postcard and note the difference.

Use a pencil eraser to draw a "warm line" on a piece of wood, then hold the contact to expose the pattern. If you work fast enough, you can even write y this way. Point your finger upwards, then hold the LC postcard right above it. A plume wafts upwards along your finger, and after awhile the LC postcard will show I found an article which mentions where large sheets of the material can be obtaine

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On other topics: have you ever heard of the lab done by an instructor years ago in TEACHER, where he had his students measure outdoor temperatures every few h winter, in particular taking many measurements when the temperature was around temperature versus time as the temperature varied across 0C, and found a peak in that as the temperature decreases, when it hits 0C it stops falling while environmen then it continues downwards again. A similar thing happened when the temperatur It wasn't a large effect, but the students were able to see it in their graphs. The inst students in coming up with sensible explanations for the existance of this "stick poi outdoor temperature versus time.

I recall running across an entry on HYPERSONICS in some encyclopedia (Britann connected up two separate fields of physics for me. It seems that as the frequency at some very high point the wavelength becomes nearly as short as the spacing bet range of frequencies the speed of sound drops radically, until the sound "oozes" rat propagating as a wave, and moves as incoherent, interacting vibrations. Also, the sound is similar to the wavelength of longwave IR radiation. The upshot: "heat ene where sound has become so high in frequency that it moves slowly and is renamed vibrations." And the wavelength of the sound is so short that it can interact with in be converted to IR light. My concept of heat energy within solids has been change to be a very very loud "hiss" of white noise, high frequency sound which propagat objects, and which also induces the objects to glow with invisible light. We live in
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