Category Archives: Science fair ideas

1937 Precision Sundial

1937OctPSaIf Junior decides to make a sundial for the Science Fair project, he or she could just order a kit from Amazon, slap it together, and hope for the best, undoubtedly a participation ribbon.

But if they have some basic mechanical aptitude, they can’t go wrong by putting together the advanced model shown here, from the October 1937 issue of Popular Science. This sundial will be able to read the correct time to within about a minute. It’s a bit more complicated to operate, but it’s quite easy once you get the hang of it.

The dial is fixed in place, with the axis pointed at the North Star. This means that the dial is mounted at an angle the same as your latitude, pointing due north. To read the time, you move the upper part of the dial so that the pointer P is casting a shadow on the figure-8 (known as the analemma.)

Once that shadow is positioned, then the time is read directly from the pointer T, which is pointing at the time. The article explains how to calibrate the dial, which has markings every five minutes. With these, you should be able to interpolate the time to within one minute. As an added bonus, the shadow on the analemma shows the approximate date.

Parts are all readily available.  The dial itself is a cake pan.



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Science Fair Idea: More Conductive Flames

1937OctPSWe’ve previously shown a science fair project showing that a flame conducts electricity.  (And if you follow that link, you’ll see links to even more spectacular projects involving electricity and flames.)  But the one shown above, from Popular Science, October 1937, is even simpler.  Junior will undoubtedly amaze the teacher with the simple elegance, and very little preparation is needed.

Because the area around the open flame is conductive, the two strips of paper will quickly discharge in its presence.  But when the experiment is repeated with a screen between the paper and the flame, there will be no effect.

All you need is a candle, a couple scraps of paper, and an old piece of screen.  And, of course, don’t forget to give your young pyromaniac a box of matches.



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Science Fair Idea: Lens Made of Air

1937AprPS1For the student looking for a simple science fair project that will mystify the teacher, you’ve come to the right place. When the teacher asks what scientific question(s) your project will demonstrate, you can propose the following:

Is it possible to construct a convex lens that will have a magnification factor of less than one? Is it possible to construct a concave lens that will have a magnification factor of more than one?

ConvexConcaveTo put it another way, a convex lens (such as the one on the left) makes things look bigger, and a concave lens (shown on the right) makes things look smaller. But your simple experiment will show that it’s possible to make a convex lens that makes things look smaller, and a concave lens that makes them look smaller.

A lens is usually made out of a substance such as glass, which is denser than air. This means that light waves travel more slowly through the lens. But there’s no reason why you have to use glass and air. In your case, you will use air for the lens, and water instead of the air. This means that the speed of light is faster through the lens, rather than slower, as we usually think of lenses.

The layout for the lens is quite simple, as you can see from the illustrations. You need a small1937AprPS3 can, covered on each side with a piece of cellophane. Any type of clear flexible plastic should work fine. The easiest option is probably cling wrap. You’ll need to cut a hole in the side of the can, and insert a flexible rubber or plastic tube. The connection needs to be air tight. There are probably other ways to make the connection, but the easiest would probably be to use a small brass tube, and solder it to the can.  (You’ll need a soldering iron, which probably costs a lot less than you would expect.)  Slide the plastic tube over the brass, and make sure the connection is water tight.  The construction details are shown at the right.

1937AprPS2If you blow into the tube, as shown in the illustration above, then the can becomes a convex lens, made out of air. And if you suck air out of the tube, as shown at the left, it becomes a concave lens. Place it in a container of water, and you can watch how a black stripe at the bottom of the container is magnified or made smaller, but the opposite of how it would work with a glass lens in air.

Your teacher will have to concede that there’s nothing in the definition of “lens” that requires it to be made out of glass. He or she will have little choice but to award you the blue ribbon for answering your questions in the affirmative.

The project appeared 85 years ago this month in the April 1937 issue of Popular Science.



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Science Fair Idea: Re-orienting Your Globe

1972MarEE

Fifty years ago this month, the March 1972 issue of Elementary Electronics showed this idea to improve the utility of the globe in your radio room. Normally, the globe is mounted so that it spins just like the Earth–along its axis. But you’re not required to spin the globe, and it becomes more useful if you orient it so that it can turn along an axis through your location and your antipode–the point furthest away from you.  If you’re in North America, that would be somewhere in the Indian Ocean.

The advantage of doing this is that it quickly lets you see the direction and distance to any other point.  The thing holding the globe in place (known as the semi-meridian) is usually marked in degrees.  But you can tape a scale in miles to it, and if you rotate any point on the globe toward that line, you’ll instantly see the number of miles.

All you need to do is remove the globe from its mounting, which is usually just a matter of slipping it out.  You then drill a new hole at your location and at the opposite side, and remount it.

The student desiring to bring home the blue ribbon at the science fair will quickly realize that this simple project will answer the question of “how to convert a globe into a distance measuring instrument.”



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Science Fair Idea: “Lens” for Sound

1937MarPSFor students looking for a simple but impressive (and slightly dangerous) science fair experiment, this one from the March 1937 issue of Popular Science is almost certain to bring home the blue ribbon. It demonstrates that sound waves can be manipulated with a “lens” in the same way that light can. In this case, the “lens” is made up of a balloon filled with carbon dioxide. Since the CO2 is heavier than air, a bubble full of this gas refracts the sound waves. This can be shown, as hear, by using the “lens” to amplify a distant sound. To prove the effect, another balloon filled with normal air can be compared.  If the teacher requires that the project answer a question, then the question can be, “can sound waves be focused in the same way as light waves?”

To generate the carbon dioxide, the method suggested by the magazine is to place some limestone into a bottle containing muriatic acid.  The balloon is placed on the bottle and quickly inflates with the carbon dioxide produced by the reaction.

WARNING: Muriatic acid is another name for hydrochloric acid, and it’s very dangerous. You need to take precautions from getting it on your skin, and especially your eyes, since it could blind you. Do this part of the experiment outside, wear eye protection, and follow these other safety precautions. But you can get the muriatic acid at your local hardware store or on Amazon.  For children too young to handle the acid, a parent or teacher can produce the carbon dioxide and give the balloon to the child. The balloon full of CO2 is perfectly safe.


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Anemometer With No Moving Parts

1957FebPE10If Junior wants to take home the blue ribbon at the next science fair, this project will almost certainly provide it. When Junior announces to the science teacher that he or she is going to build an anemometer (an instrument for measuring wind speed) with no moving parts, the teacher will be mystified, and will wonder whether it is even possible. But when they see the completed device in action, they will be astonished at its simplicity.

1957FebPE11The anemometer consists of a Wheatstone bridge circuit, which consists of four resistors. Two of the resistors are actually thermistors of equal value. As long as their resistance remains equal, the meter shows a reading of zero. But if they are unequal, then the meter displays a current. The two thermistors are placed outside at the spot where the wind is to be measured. When they are energized, they heat up slightly, which causes their resistance to change. As shown at left, both are mounted in a small plastic container, but one of those containers has small holes drilled in it. When it is exposed to the wind, it is cooled, but the other thermistor is not. The stronger the wind, the greater the cooling, and the current increases. In other words, as the wind increases, it is shown on the meter.

Once the meter is built, it needs to be calibrated, and that requires Junior to “enlist the services of a competent automobile driver” on a “highway which permits maximum state speed limits.” The driver accelerates to 60 MPH, and Junior holds the thermistor assembly out the window, as far as possible. (We note that Junior should take care not to have the arm amputated by a passing truck.) Junior then adjusts the instrument so that it indicates a full scale reading on the meter. The measurement is taken again at different speeds, and the meter reading is noted.

When Junior is awarded the blue ribbon for this elegantly simple design, the teacher will undoubtedly be thinking, “why didn’t I think of that?”

The original construction article, from the February 1957 issue of Popular Electronics, called for a “matched pair” of thermistors, since they need to have equal values. While it might not be possible to buy a matched pair, there is an inexpensive alternative. Junior can buy this set of 100 thermistors on Amazon at a very reasonable price. It includes 10 each of different values, including the needed 2kΩ. Junior just needs to measure all ten, and then use the two that are the closest in value. The remaining 98 thermistors can be used for other experiments. In fact, by adjusting the values of the other resistors, another value of thermistor could be used.

1957FebPE22



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Illusion: Candle Burning in Bottle of Water

1937FebPS01For a simple illusion that can be part of a science fair project, this self-explanatory diagram shows how to make a candle look like it’s burning inside a bottle of water.

A plate of glass is placed as shown.  Since it allows light to pass through, but also reflects light, when it’s viewed at the correct angle, it appears that the candle is inside the bottle of water.

This idea appeared 85 years ago this month in the February 1937 issue of Popular Science.



 

Party Game Idea

1961DecRadioConstrSixty years ago this month, the December 1961 issue of the British publication Radio Constructor gave some ideas for devices to liven up a Christmas party or, for that matter, any party. According to the author, the self-explanatory design here was an “oldie,” but was largely forgotten. To play the game, one needed to move the ring from one side to the other without touching the metal rod.  According to the magazine, this feat required a remarkably steady hand, and was no doubt good for many hours of fun as the guests made an attempt.

The magazine noted that if the party was one for charity, then the guests could be charged a fee to play, earning a refund if they were able to successfully move the ring from one side to the other without sounding the bell.

Perhaps if Junior is looking for a science fair project, this one could be used as a basis for determining which of their classmates had the steadiest hand.



Science Fair Idea: Electrostatic Precipitator

1946DecPS1946DecPS2Seventy-five years ago this month, this young woman undoubtedly took home the blue ribbon of the 1946 Science Fair with this experiment in which she constructed an electrostatic precipitator to fight air pollution.  In the photo above, a column of smoke is rising.  But the moment she flips the power switch on her precipitator, the smoke ceases.  An electrostatic precipitator, known at the time as a Cottrell precipitator after its inventor Frederick Gardner Cottrell, removes particulate matter from the air through an electric charge, but does not affect the flow of gas. The same principle is used in home air purifiers such as this:

In the 1946 experiment, a column of polluted air passes through a mailing tube, where it passes through a high voltage electric field. Particulate matter clumps together as a result of the electric charge, and falls to the bottom of the tube.

We enjoy providing inspiration for projects such as these, and we hope modern school children can do the same experiments. And for this project, your young scientist will need the following items. Where available, we have provided links to Amazon:

As you see, Amazon no longer has all of the needed parts. The Model T spark coil is apparently out of production. And while this young woman had no problem bringing a pack of Chesterfields to school and nonchalantly lighting one up in the science classroom to show off her invention, it’s no longer 1946. If a kid did that today, they would probably get expelled. So if Junior wants to do this experiment today, some modification is necessary.

Fortunately, as long as your young scientist has some creativity, substitutions shouldn’t be a problem. In place of the cigarette, the original 1946 experiment allows for the use of an incense stick, and as long as Junior has the teacher’s permission, this shouldn’t be a problem.

The Model T spark coil, however, is a bit more problematic. The spark coil from a Model T was known as a trembler coil.  The device was a transformer. To be able to operate with DC, the coil operated in interrupter: When voltage was applied to the coil, the magnetic field opened the contacts of the interrupter, which turned off the coil. With the coil off, the contacts closed, allowing the coil to re-energize. The result of this on-off action was an alternating current, and the voltage of this alternating current was stepped up to thousands of volts with the transformer.

The Model T spark coil remained in production for many years after the last Model T rolled off the assembly line, and many of them found their way into things other than cars. When this experiment was published in Popular Science in December 1946, there was apparently no question that if you wanted a Model T spark coil, that finding one wouldn’t be a problem. One popular use of the coil in the early days of radio was for use in a spark-gap transmitter.

But if you walk in to the parts counter of your local Ford dealer today, they probably don’t have them any more. (On the other hand, there are still Model T’s on the road, and if you want to buy a new spark coil, they are still being made, but they’re probably too expensive, such as this one.)

The advanced student should be able to build their own induction coil. They will need a transformer and a method of interrupting the current. Experimentation with a filament transformer and mechanical buzzer will probably prove fruitful. Our earlier post describing a spark coil should give the advanced student enough information to construct one that is essentially identical to the Model T version.

The school might already have the equivalent stashed away in the back room of the science lab, or you could convince the teacher to spend some of the science budget on one of these:

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1961 Student-Built Radio Telescope

1961NovEISixty years ago this month, the November 1961 issue of Electronics Illustrated featured this radio telescope constructed by high school student H. Mark Wahl of Cheyenne, Wyoming. The rack containing the electronics was a school locker. The door of the locker was removed to form the door, and the equipment was mounted facing what used to be the back.

The equipment consisted of a standard FM broadcast receiver which had been converted to AM by eliminating the limiter and discriminator. A tuned RF amplifier, apparently for 108 MHz, was added to beef up the sensitivity. The IF output was connected to what looks like a Hallicrafters S-30B tuned to 10.7 MHz. This fed two recorders, one connected to the voice coil of the receiver’s speaker, and the other one connected to the S-meter. The recording of the audio output was accomplished with a pivoted wooden arm. The other end held a pen which recorded on a strip of paper driven by a motor.

The recorder hooked to the meter consisted of a straw from a broom, which recorded a trace on a soot-covered cylinder turned by a wind-up alarm clock, creating a 12 hour record.

The antenna consisted of two folded dipole antennas, probably made out of TV twin lead, mounted horizontally and parallel to each other, about a hundred feet apart. With identical lengths of feed line, the signals would arrive in phase, and be identical. The antenna pattern would have a number of lobes, one of which was straight up. However, if an additional half wavelength of feedline was added to one side, the two signals would arrive out of phase. The pattern would be similar, but the signal from straight up would be nulled out. By using the difference of these two signals, the interferometer was able to null out everything but the signal from straight up. Thus, any terrestrial interference would be eliminated, and the antenna would see only the cosmic noise coming in from directly overhead.

While we think of most radio astronomy taking place at higher frequencies, there’s no reason why frequencies just above the FM broadcast band can’t be used. For example, this 2014 experiment used 38 European radio telescopes to detect radio signals from a distant galaxy on 115 MHz. Those 38 dish antennas probably provided a better signal than two folded dipoles a hundred feet apart, but they used the same principles to combine the signals.

Unfortunately, the article doesn’t give too many practical details on the construction of the set. And other than the author’s assertion that it was “relatively simple, but it works,” there’s little detail on what observations he made.

We’ve previously written about another group of students in Britain who built a radio telescope in 1959.  This website specializes in science fair projects that a student and frazzled parents can whip together in one evening, and we have many that fit that category.  Building your own radio telescope is definitely not in that category. But students were doing so 60 years ago, and there’s really no reason why an advanced student (or maybe a student who’s not so advanced, but just likes to tinker with electronics) can’t do the same thing today.



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