Category Archives: Science fair ideas

1941 Optical Communicator

1941AugPS1Eighty years ago, this well dressed gentleman was sending a message through this light beam transmitter, as described in the August 1941 issue of Popular Science.

The magazine was a bit prophetic, since there was more experimentation with the idea after Pearl Harbor. When hams were ordered off the air for the duration of the war, optical communications was one of the ways they continued to practice their hobby (along with carrier current communications.)

The idea is simplicity itself, and it’s an idea that I independently invented as a youngster 30 years later, and I know others did as well. The light beam of a flashlight is modulated with an audio signal by wiring the light in series with the secondary of a transformer. The primary of the transformer is wired with a buzzer and key to send Morse code. When I did the same thing, I hooked the transformer primary to the output of a transistor radio or other audio amplifier, allowing voice signals to be sent.

The receiver is an audio amplifier, with a photoelectric tube hooked to the input. In my later experiments, I used a solar cell hooked directly to the input of an amplifier, which didn’t seem to mind the small DC voltage.

The student looking for an interesting project for a science fair could easily duplicate this experiment with modern equipment, at very low cost.  It’s an easy demonstration of a communications device dependent only upon light.

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1911 Homemade Alarm Clock

1911JunePopElec110 years ago, a young John Long of Leechburg, PA, sent in this self-explanatory idea for building an alarm clock to the “Young Edisons” department of Popular Electricity magazine.

The magazine carried the feature of letters from readers of its Junior Department. Letters were to accurately and briefly describe experiences in the making and operation of electrical devices and the performance of electrical experiments. The magazine asked readers, “see how good an ‘engineering report’ you can make of your investigations.”

Young Mr. Long constructed this alarm switch with a battery, door bell, and pocket watch.

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Human Reflex Science Fair Project

1941JunePSIf Junior is looking for an interesting demonstration for the first post-COVID science fair, he or she can’t go wrong with this illustration of how human reflexes work.  If you touch a hot stove, your body needs to react before the brain kicks in.  Therefore, you are hardwired to jerk your hand away.

This demonstration illustrates the principle.  A flame is brought close to a simulated human hand, but as soon as it comes into contact with the simulated nerve, the solenoid energizes and jerks the hand away.

The idea appeared 80 years ago this month in the June 1941 issue of Popular Science.  For the young scientist wishing to duplicate the project, all of the parts are readily available on Amazon:  This switch will kick in at 40 degrees Celsius, an uncomfortably warm, but not dangerous temperature.  This 3-volt solenoid will reliably move the hand.  And there’s no need for the old-school dry cell batteries shown above.  Alkaline D cells will work very well, especially if you have a battery holder for them.   And while Junior can make the hand out of cardboard, he or she will be virtually guaranteed the blue ribbon with a realistic looking plastic hand.

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Homemade Cardiac Monitor: 1961

1961JunePEIf Junior is looking for a spectacular science project in the field of biomedical engineering, this one is a sure winner.

Sixty years ago, the June 1961 issue of Popular Electronics showed how to construct this simple cardiac monitor. The circuit was simple, amounting to a 4 transistor audio amplifier. The diagram called for 2N279 transistors, which are apparently unobtainium today, but this substitution guide lists the 2N2431 as equivalent, and it is available at a reasonable price.

The input comes from two electrodes, one of which is placed on each arm. In this position, they will pick up the currents from the heart, which are alternating currents of up to 100 kHz. The audio portions will be audible in the headphones, and also displayed on the meter. The magazine notes that you are not hearing the actual sound of the heart, merely the amplified voltage sent to the heart muscle. Other muscles can be monitored by placing the electrodes on either side of the muscle in question.

The electrodes are simply pieces of metal placed on the body. Prior to placing them, the skin needs to be scrubbed to improve the conductivity. This is done by scrubbing with Lava soap
or Ajax cleanser. (However, since Ajax is now billed as “non-scratching”, I’m not sure it would still work.) The article notes that the device is completely safe, even for children. First of all, it runs off only three volts. And the connection to the electrodes goes through a capacitor, so even that voltage has no pathway to the body.

More advanced versions are available today, but the advanced student will almost certainly bring home the blue ribbon in the science fair by building the medical device at home.

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Homemade Boxes

1921MayPSA hundred years ago this month, the May 1921 issue of Popular Science showed how to make your own boxes. According to the item, it was frequently the case that you needed a box, but didn’t have one of the proper shape and size. With a piece of stout paper, it was possible to make one yourself capable of containing solids, even paper. And if you needed a container for liquids, the same could be done with parafined paper (what we would call wax paper today).

In addition to the practical uses around the house, the younger student looking for a science fair project could compare the qualities of various types of paper in forming boxes.  Of course, if one needs a box with a lid, a second, slightly larger, box could be made to slip snugly over the first.

The idea had been sent in to the magazine by one Peter P. Lembo.



1941 Electrical Science Fair Ideas

1941AprilPSbuzzerIf Junior wants to take home the Blue Ribbon in the science fair, there’s plenty of inspiration to be found in the April 1941 issue of Popular Science. Some of these ideas might look difficult to some kids today, but the smart students will realize that they are really quite simple. One or more of these ideas is sure to impress the judges.

The idea shown above is a simple buzzer. When the battery is connected, the electromagnet pulls the strip of metal away from the screw. This breaks the contact, and the strip snaps back into place, and the whole process is repeated.

1941AprilPSthermostatShown at left is a simple thermostat.  It’s made of a strip of iron and a strip of copper or brass, bolted together.  When the temperature changes, they expand or contract unequally, causing it to bend to one side.  Simply add an electrical contact at just the right spot, and a circuit will turn on or off at a given temperature.

The self-explanatory experiment to the right uses a thin strip of foil to demonstrate1941AprilPSfuse how a fuse works.  Simply cut it narrow enough so that it blows when a short-circuit is applied.

The experiment shown below is similar to one we featured recently.  It uses a transformer designed to convert 120 volts to 6 volts, but shows that the process can be reversed to change a low voltage to a high voltage.  As in the experiment we showed earlier, a wire is run along a file to create a pseudo-alternating current at the low voltage.

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The final experiment is also similar to one we’ve shown previously.  A homemade microphone is made by balancing a pencil lead on two razor blades.

1941AprilPSmicrophone

Even though all of these experiments use the old-school large dry cells, they will work just as well with alkaline D cells.  The hookup will be easier if you purchase battery holders.  And don’t forget some wire.

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High School, 1946

1946Apr22LifeShown on the cover of Life Magazine 75 years ago today, April 22, 1946, is Marilyn Rights, a junior at Denver East High School, in her Latin class. She would have been in seventh grade for Pearl Harbor, and most of her high school career took place during the war. The magazine profiled the school, and also took a look at the tension between two competing points of view.

1946Apr22LifeTyping One view, championed by the National Education Association, called for more practical program for high school. Harvard University, on the other hand, called for more emphasis on cultural and academic subjects. The magazine’s focus was on how well the school was measuring up under the two competing plans. Harvard would be pleased to see Miss Rights’ studious attack of Latin, whereas the NEA would probably be pleased with the typing class shown here. The magazine noted that the class was one of the most popular at the school. While it was originally intended for “commercial students,” it was open to other students who learned typing in order to prepare neater homework.

1946Apr22LifeColdCreamAt least one of the courses, practical chemistry, allowed students to learn about cosmetics by manufacturing their own cold cream, probably with a formula such as this one involving borax.

The psychology class appears to be much more interesting than the one I took in college. Here, we1946Apr22LifeMovie see the class on a field trip to see Ingrid Bergman in Spellbound, which deals with psychiatry. They discussed the film in class, and were critical of its superficial psychiatric approach. Those same students were also engrossed in the simple science experiment shown below, demonstrating how sound is transmitted to the ear. The spoon was tapped to the desk to make it vibrate, and the string held to the ear to demonstrate how the vibrations traveled through the string. In fact, elementary students looking for a simple experiment for the science fair can conduct this experiment, which you can see described at this site.

1946Apr22LifeSpoon

Another interesting activity in the psychology class is shown in the sociogram of the class below. Each student was asked to name their two best friends in the class, and these links were plotted on the chart. This revealed that the class consisted of four distinct “cliques,” which were largely independent. Girls 12 and 15 were revealed to be the most popular, with four students each identifying them as a friend. Interestingly, each was member of a separate clique. Girl 25 is identified as a “typical lonely student,” who chose students 4 and 11 as her best friends, but was herself chosen as best friend by no other student. Interestingly, though, she is the only student who links two cliques. One of her friends, 11, is a member of the clique at the left, and her other friend, 4, is a member of the lower clique.

1946Apr22LifeSociogram



Vinegar and Baking Soda Experiments: Beyond the Volcano

1951MarBLEvery self-respecting young mad scientist probably discovered as a toddler that many hours of fun could be had by mixing vinegar and baking soda. When the time comes for their first science fair in elementary school, many of them harken back to this early experiment and decide to make a vinegar and baking soda volcano. In fact, if you Google the words “science fair vinegar and baking soda volcano“, you will get over a million results, many of which we are sure are fine educational projects. But we also know that our readers, even the youngest ones, strive for a bit more. So if your young mad scientist is thinking of a science fair project involving these venerable home chemicals, here are a couple of more advanced projects, which appeared in Boys’ Life magazine 70 years ago this month, March 1951. They are just as easy (or even easier) than the stereotypical volcano that other kids will be bringing, but they demonstrate some additional scientific principles.

To do the experiment shown above, you start with a tall glass of water and add a tablespoon of vinegar. You then slowly stir in a half teaspoon of baking soda. Finally, you put four or five mothballs in the glass. They’re heavier than water and will sink to the bottom, but after about a minute, they will rise to the surface. They’ll sink again and continue rising and falling for hours.

What’s happening is that the mothballs are only slightly heavier than water. Little carbon dioxide bubbles affix themselves to the surface, which gives just enough buoyancy for them to rise. At the surface, the bubbles pop, and the mothball sinks again. If you don’t have any mothballs around the house, I’m told that raisins will work just as well.

1951MarBL2If Junior likes playing with fire (and what kid doesn’t?), they will enjoy the experiment shown at the left. You start with a teaspoon of baking soda at the bottom of an empty glass. To this, you add a tablespoon of vinegar diluted with a tablespoon of water. When the mixture begins to fizz, you lower a lighted candle into the glass. Since carbon dioxide is heavier than air, it fills the glass. And since carbon dioxide doesn’t support a flame (which is why fire extinguishers use it), the flame extinguishes itself.

But there’s more! If you act quickly enough, you can lift the candle back out as soon as it goes out, and the flame will miraculously come back to life. This is because there is still vaporized wax, and the wick is still hot enough to ignite as soon as it gets back into sufficient oxygen.

The kid who made the volcano will undoubtedly go home with a nice participation ribbon. But armed with these simple experiments proving scientific principles, Junior will undoubtedly take home the blue ribbon.



Parabolic Reflector Science Fair Project

1921MarSciInvIf Junior is looking for a science fair project involving acoustics, then this one from a hundred years ago will fit the bill. It’s simple to create but has a spectacular result. And as an added bonus, it promotes communication despite social distancing, since it is possible to whisper to someone about 20 feet away.

The diagram above is more or less self-explanatory. Two umbrellas are carefully placed on chairs as shown, and they serve as parabolic reflectors. The alignment is very critical, and it is recommended that a piece of string be used to keep the umbrellas exactly in line. In addition, each umbrella is thoroughly soaked in water, as this ensures that sound is completely reflected. While Junior whispers into one umbrella, the sound is heard by someone with their ear at the focus of the other umbrella. The sound seems to come from the closest umbrella.

The diagram and explanation appeared a hundred years ago this month in the March 1921 issue of Science and Invention.  The idea had been sent to the magazine by S. Leonard Bastin.

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Science Fair Project: Tide Predicting Machine

1921MarPSA hundred years ago, this scientist is predicting the tides with the help of this tide predicting machine, described in the March 1921 issue of Popular Science.

The machine is an analog computer, one version of which was fittingly dubbed Old Brass Brains.  The first such machine was designed by Lord Kelvin, who noted that the tide at any particular location was the sum of a number of sinusoidal functions in the form:

A_{1}\cos(\omega _{1}t+\phi _{1})+A_{2}\cos(\omega _{2}t+\phi _{2})+A_{3}\cos(\omega _{3}t+\phi _{3})+\ldots

Prior to the advent of the digital computer, such a computation would be laborious, especially if one needed to repeat it to calculate the tide minute by minute. But with the analog computer, once the various constants were set, it was simply a matter of turning a crank and seeing what the tide was at any given time.

Each term of this equation is represented in the machine by a wheel similar to the one shown at the left.  As the wheel turns, the piece in the middle moves up and down, and the distance moved up or down is proportional to the cosine of the angle at which the wheel is turned.  By changing the position of the pin and the size of the wheel, the various constants in the equation are taken into account.  The output of this wheel is then linked by a pulley to the next wheel.

Replicating such a machine in its entirety would, of course, cost millions of dollars in precision machining.  However, the advanced student could create a very impressive science fair project by constructing a part of such a machine, namely one of these wheels, or perhaps even link two wheels together.  With information from the WIkipedia articles and Popular Science article linked here, a very impressive exhibit could be created.