Category Archives: Science fair ideas

1961 Student-Built Radio Telescope

Sixty 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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Science Fair Idea: Global Warming & Obliquity of the Ecliptic

If Junior wants to perform a somewhat contrarian and controversial science fair experiment, he or she can perform an experiment to answer the following question:

“Can global warming be caused by reduction in the obliquity of the ecliptic?”

The science teacher won’t be able to react immediately, because he or she probably doesn’t know what “obliquity of the ecliptic” is. But after they consult Wikipedia, they’ll understand the concept, and they might have to grudgingly concede that there’s something to it. “Obliquity of the ecliptic” is just a fancy term for the angle at which Earth’s axis of rotation is tilted. Today, it’s about 23.4 degrees. But 8000 years ago, it was 24.2 degrees, and it’s been going down ever since.

With this experiment from 85 years ago, Junior will be able to demonstrate that as the tilt decreases, the ice pack at the poles will increase. In the illustration above, the Earth is covered with “ice” to about the same extent that it is today–it’s north of the Arctic Circle. But if the tilt is increased, the extent of the ice pack covers much more of the hemisphere, as shown at left.

The experiment to demonstrate this appeared in Popular Science 85 years ago this month, November 1936. The Earth is represented by a rubber ball. A hole is drilled through the center and a knitting needle is inserted, to serve as the axis. The earth is then dipped in melted paraffin wax and covered to a depth of about 1/16 inch, representing ice. A high-wattage light bulb serves as the sun, and the ball is mounted as shown and rotated. After about a half hour, a layer of wax covers the area north of the Arctic Circle. The remaining wax drips off onto the mounting board. In the real world, this melted ice would enter the oceans.

The experiment is then repeated with a larger angle, and the “ice” covers much of the hemisphere. Junior has demonstrated that the extent of arctic ice increases as the obliquity of the ecliptic increases, and decreases as the obliquity of the ecliptic decreases. Since the obliquity of the ecliptic is currently decreasing, it stands to reason that this is a cause of the arctic ice decreasing. And if the teacher believes that some other cause is at work, then he or she can come up with an experiment. Junior can remind the teacher that this is how science works.

Which is Cheaper: Gasoline or Ethanol?

Gasoline versus Ethanol

Wikipedia image.

Shown above is a molecule of ethyl alcohol, also known as ethanol. If you ignite it with a spark, it will burn. This is not rocket science. (Come to think of it, though, if you use it as rocket fuel, then it is rocket science.) Gasoline (or petrol, as our friends across the pond like to call it) is a mixture of molecules, most of which look very similar to the one above. If you ignite it with a spark, it will also burn. The difference, however, is the “O“. Gasoline doesn’t have any oxygen atoms. To burn it, you need to supply all of the oxygen from another source. Fortunately, that’s easy to do, since we live in an atmosphere consisting partly of oxygen, and it’s free for the taking.

But this means that for a given amount of fuel, the ethanol will have less energy content: If you burn gasoline, you can use the free oxygen that is floating around. If you use ethanol, then you are paying for some of the oxygen, which you could have gotten for free.

For this reason, I’ve heard many people explain that you shouldn’t use ethanol as fuel, because your fuel mileage will be lower. But that’s not the end of the discussion: If you’re like me, you are really concerned about saving money, and your main concern is which fuel is cheaper.

A Real World Comparison Test

I’ve heard many persons express their opinion as to the relative fuel economy, but I’ve never heard anyone actually test it, so I decided to do so myself. I recently had to drive from St. Paul, MN, to Escanaba, MI, to do an FCC Great Lakes Ship Radio Inspection. I drove eastbound using e85, a mixture of approximately 85% ethanol and 15% gasoline, and drove westbound with gasoline (which is actually e10, 90% gasoline and 10% ethanol). For the nitpickers, here are the conditions of the test:

To make sure I was able to purge almost all of the E85 from the system before the return trip, I tested the mileage from St. Paul, MN, to Marinette, WI, short of my final destination. I started with a full tank, and upon arriving in Marinette, I checked the cumulative mileage and then added about 6 gallons. I also added a few gallons in Escanaba, MI, about 56 miles away. When I arrived back in Marinette, I was down to about a quarter tank, at which point I filled with gasoline (actually, e10) for the trip home. So almost all of the e85 had been purged from the system for the trip home.

My vehicle is a 2014 Dodge Journey with the 3.6 liter 6 cylinder engine. The EPA estimated highway mileage is 25 MPG with gasoline, and 18 MPG with e85. The two endpoints have similar elevations (795 feet in St. Paul, versus 594 in Marinette). Winds on the day of my trip were light, and whenever I did see flags moving in the breeze, the prevailing wind seemed to be from the north. So there should be no effect from a headwind or tailwind. I took an identical route both directions, mostly over four lane freeways, but a small portion over county highways suggested by Google. In other words, the driving conditions both directions were more or less identical. The average mileage reading was taken from the car’s computer, which was reset after each fill-up.

The average mileage using e85 was 21.6 MPG. The average mileage using gasoline (actually e10) was 26.4 MPG. As noted above, the mileage with ethanol was lower, since the fuel has a lower energy content. The real question is which fuel is cheaper.

To make the comparison fair, I’ll use the prices at the same station, the one where I bought the e85: The e85 cost $2.229 per gallon. In other words, it cost me $2.229 to drive 21.6 miles, or 10.32 cents per mile. (I actually used a loyalty card, which brought the cost down to $2.029 per gallon, or 9.4 cents per mile).

The gasoline I bought for the return trip cost $3.239 per gallon, since one gallon allows me to drive 26.4 miles, that means I spent 12.3 cents per mile. But in fairness, if I had bought that gas for the eastbound trip at the same place where I bought the e85, it would have cost $3.099 per gallon, which works out to 11.7 cents per mile.

In other words, it was cheaper to drive using the e85: 10.3 cents per mile versus 11.7 cents per mile. In other words, the e85 is 12% cheaper than using gasoline.

It should be noted that these figures are based upon the price at one particular station, a Holiday gas station. You can view the current prices at this station at this link. Some gas stations sell e85, but at a much smaller discount over the price of regular gasoline. In fact, I’ve occasionally seeing a station inexplicably selling e85 for more than the price of regular gasoline. Obviously, it makes no sense to buy to buy there. To be economical, the price of e85 needs to be below 21.6/26.4 = 82% the price of regular gas. In my case, the price of e85 was 74% the cost, and thus a clear bargain.

Other Considerations

There are a couple of other factors to keep in mind. Even though the name of the fuel is “e85” the exact blend can vary. During the winter months, the gasoline content is higher, and I have noticed that stations do not adjust the price based upon the exact mix. So during the winter, the e85 might be an even greater bargain.

Also, I have not measured it, but I have noticed that when I have a mixture that is around 50% ethanol and 50% gasoline, I don’t notice much mileage difference between it and 100% gasoline. So even though the energy content is lower, the actual effect on mileage might not be linear. It would be interesting to repeat this experiment with different blends.

I’m not sure of this, but I suspect that for applications requiring more power (such as towing), gasoline would have a greater advantage. But again, I’ve not tested this hypothesis.

And you will certainly have more range using gasoline than you would ethanol. So if cost isn’t an issue, but you need to drive as far as possible before refueling, then you will be able to drive 22% further by using gasoline.

I suspect that ethanol might have a greater cost advantage for high altitude driving. The reason why there is a lower energy content is because the fuel contains oxygen, which is available at no cost from the atmosphere. At higher elevations, the additional oxygen in the fuel might be an advantage.

Precisely because it has a lower energy content, ethanol also increases the octane rating of the fuel, so it is an inexpensive option for use in high compression engines.

Ideas for Young Scientists

If students are looking for an interesting science fair project, I hope my little experiment has given you some ideas. Even if you don’t have a driver’s license, you can recruit your parents to keep track of mileage when driving, and compare different fuels, or different types of driving, to see which is the most economical.

Interestingly, I exceeded the EPA mileage estimates for both fuels. There was a time when the EPA estimates were overly optimistic, but I guess those days are gone.

But Ethanol Will Clog My Fuel Filter!

Someone will invariably claim that ethanol clogs fuel filters, and I want to explain what is really happening. Alcohol can mix with both water and gasoline. Water, by itself, cannot mix with gasoline. If you have 100% gasoline in your tank and some water is added, it is heavier than gasoline and will settle to the sump at the bottom of the tank, which is below the point where it can be drawn out by the fuel pump. It doesn’t do any harm there, as long as it stays below the level of the fuel intake. But it does dissolve dirt, and that dirt has nowhere to go but stay in the water.

Eventually, if water keeps getting added, it will continue to collect. If it ever gets up to the level of the intake, then this will be a problem, since water mixed with dirt will be going to the engine rather than gasoline. The fuel filter will clean out the dirt, but the engine will try to burn the water, and water doesn’t burn.

When ethanol was first added to gasoline in the U.S., this meant that it found its way, for the first time, into cars with water in the bottom of the tank. The alcohol allowed the water and dirt to mix with the gasoline. The dirt, which may have collected since the car was new, went into the fuel filter, as the filter was designed to do. This is how ethanol got a reputation for clogging fuel filters.

But now, virtually all gasoline sold in the U.S. contains at least 10% ethanol, and virtually every car on the road has been burning 10% ethanol for years. Water never gets a chance to build up in the tank. If there is dirt in the tank, it comes out constantly. Unlike the time the car got its first tank of ethanol, years’ accumulation of dirt is not coming out all at once to suddenly clog the filter. So after that initial shock, ethanol actually corrects the problem, and also prevents gas line freeze. In the days before ethanol fuel, in cold climates, people bought a product called Heet to prevent fuel line freezing. This consisted either of ethanol or isopropyl alcohol. Since ethanol is now included in the fuel, this is no longer necessary, and you rarely hear of gas lines freezing.

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Science Fair Project: Homemade Battery

If Junior is looking for a project for the science fair, a good standby is always making a battery out of materials found around the house. We’ve previously covered the idea in more detail, but the October 1961 issue of Popular Electronics shows a slight variation. All of these are a variation of Allesandro Volta‘s Voltaic pile from 1799, and are easy to recreate.

This one uses strips of copper and aluminum. The mechanical details are unimportant, so you don’t have to worry about the exact shape. The aluminum can be cut from a soda can, although these have a plastic lining on one side and paint on the other, so the aluminum will need to be sanded. If you don’t have a strip of copper available, a piece of copper wire, or any kind of copper hardware found at your local hardware store will work fine.

The 1961 article uses the battery to power a one-transistor radio. As you can see below, it consists of a crystal set with one germanium transistor amplifying the audio. But to show that the battery is working, a light emitting diode would work just fine. Polarity is important, so if it doesn’t light at first, simply reverse it in the circuit. In this battery, the copper is positive, and the aluminum is negative. It will come to life when the two electrodes are placed in salt water. As shown in this picture, you can carefully put one drop between the electrodes, or simply place it upside down in a glass of salt water.

Junior’s experiment for the science fair can be to see how much salt in the water results in the brightest glow. Or he or she can try different electrolytes, such as bleach or lemon juice. Very little can go wrong, and as long as some liquid is between the two strips, the LED is almost certain to give off a little light.

As we noted previously, the project is very easy with materials found around the house. But for students who want to bypass the procurement process, you can simply go out and buy one of the potato clocks shown at left.

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1921 Homemade Phonograph

A hundred years ago, the cost of a phonograph was becoming reasonable so that most Americans could afford one. But for the frugal handyman, there was another option, as shown here in the October 1921 issue of Popular Science.

Not only could the home craftsman make his own phonograph and save some money, but the homemade version would be superior to most commercial phonographs. The majority of the machines were hand-crank phonographs, but this one was electric, relying on a motor powered either by batteries or household current.

The platter was made of a piece of brass, with another strip of brass soldered to the edge. This was driven by the motor using a friction drive made of a typewriter eraser
like the one shown here. Surprisingly, you can still buy a manual typewriter, but this style of typewriter eraser is no longer made. Like everything, however, you can find them on eBay.

The magazine explains how to construct the pickup and tone arm, which consists of a brass tube and the lid from a jelly jar. The board at the rear not only supports the tone arm, but serves as a sounding board, presumably providing room-filling audio.

One issue that is not addressed by the article is how to regulate the speed, since the motor will need to be spinning at about the right number of revolutions per minute. The relative size of the eraser and platter will, of course, provide some gearing, and there would be some room for experimentation. And with a DC motor, the voltage could be used to get the speed right. But the motor is going to have to start out at approximately the right speed, so some experimentation would be necessary for which motor to use.

As long as the craftsman got the bugs worked out, the result would be a quality phonograph, albeit not as aesthetically pleasing as the one normally found in the parlor. Students looking for an interesting science fair project can follow the instructions provided by Mr. Wizard in the video below. All you need is a pencil, a pin, a piece of construction paper, some tape, and, of course, a record that you don’t mind suffering possible damage.

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1921 Signaling Device

A hundred years ago this month, the October 1921 issue of Popular Science showed this signaling device for use by the military. It provided a level of security, because its light beam was visible only over a small area. It’s a very simple idea–it consists of a telescope with a flashlight bulb mounted inside at the focal point. It was easily aimed by looking through the telescope. The bulb’s filament was visible, and it was simply a matter of lining it up so that was visible over the spot where you wanted your signal seen.

Students looking for a science fair project could easily recreate this. All that’s needed is a toy telescope like the one shown here. It can be carefully disassembled and the bulb place inside. You can use the bulb from an old flashlight, or buy the bulb separately. For this project an old-fashioned incandescent bulb will work better than an LED.

You’ll also need some hookup wire and batteries. While not absolutely necessary, a battery holder will make the job a lot easier. Normally, for a science project involving light bulbs, it’s most convenient to get a socket for the bulb. However, in this case, the socket might not fit. Therefore, the best option would be to solder the wires directly to the bulb. A soldering iron, complete with solder and everything else you need, is surprisingly inexpensive.

To send Morse code, you’ll also need a small pushbutton switch.

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1941 Electro-Mechanical Oscillator

This site often features science fair projects, and we often specialize in impressive projects that can be whipped together in one evening. This project doesn’t come in that category, but the advanced student who is willing to do some tinkering can replicate this tuning fork oscillator from the October 1941 issue of General Radio Experimenter.

Shown above is a tuning-fork oscillator utilizing a vacuum tube and a tuning fork. It is used to produce a very precise audio tone using an electro-mechanical process. The vacuum tube serves as the oscillator (and a modern recreation could just as easily use a transistor), and a mechanical tuning fork serves to determine the frequency. A simplified schematic diagram is shown below. The tuning fork needs to be ferrous in order for it to work.

WWV 1927 frequency standard. Wikipedia image.

A similar circuit was used for the frequency standard for WWV in 1927, as shown at the left. Advanced students wishing to duplicate this project will find some guidance at this site and this site. Students looking for the more familiar last-minute but impressive projects can browse our science fair category for ideas.

Science Fair Idea: Airfoils

If Junior likes playing with matches, and the due date for the science fair project is rapidly approaching, then the perfect project can be found in the September 1941 issue of Popular Science. This experiment answers the question, “which surface provides the least wind resistance,” and it turns out the answer is the airfoil.

Junior can easily demonstrate this with the self-explanatory experiment shown here. With the piece of cardboard flat, drag is produced, and when you blow toward the flame, it actually moves back toward you. But when the card is bent into a teardrop shape, scientifically known as an airfoil, then the air blows the flame away.

Science Fair Idea: Clothing to Keep You Cool

If Junior just remembered that the science fair project is due tomorrow, and it hasn’t even been started, you’ve come to the right place. This last-minute experiment from 80 years ago will prove an important scientific principle, you have everything you need around the house, and the teacher will be suitably impressed at Junior’s ingenuity. The teacher needn’t suspect that the project was put off until the last minute.

This project answers the simple question, “what kind of clothing keeps you cooler?” It turns out that it’s light colored clothing. All you need is a couple of pieces of cardboard, a table lamp, and a little bit of wax. If you can’t find any wax around the house, you can always go to the closest all-night supermarket and buy a package of birthday candles.

While you are out buying the wax, Junior should cut out the two small human figures, one from a piece of white cardboard, and one from a piece of black cardboard. If you can’t find any black cardboard, just make the both out of white cardboard and color one with a black magic marker. The arms should be made separately, and the arm is attached with a small drop of wax. If Junior is not old enough to play with matches, then an adult should light the candle and place a drop of wax in the correct spot.

Then, you stand up both of the figures and shine a lamp on them. You want the hottest lamp you can find, so don’t mess around with energy-efficient bulbs.

Eventually, one of the figures will get hot enough that its arm will fall off. Unless the laws of physics have changed in the last 80 years (hint: they haven’t), it will be the one in dark clothing. Junior has proven that you will be cooler if you wear light clothing on a hot day.

The experiment appeared in the August 1941 issue of Popular Science.

Science Fair Ideas: Center of Mass & Sound Waves

If Junior just announced that the science fair project is due tomorrow, but the project hasn’t even been started, there’s no need to panic. Thanks to these simple projects from 85 years ago, it’s still possible to get an A on the assignment, and the teacher will assume that many weeks of planning went into the project.

Shown above is a simple method of determining the center of gravity (or, since the teacher will prefer the more scientifically accurate term, the center of mass) of an object. Cardboard is used, but any similar substance of uniform thickness will work fine. After the pattern is cut out, the design is hung by one edge. A plum line (which is just a piece of string, with a weight on one end) is hung from the same point, and it is traced on the item. Then, it’s hung from another edge. Where the two lines intersect, that is the center of mass.

The other project, shown below, gives a visual indication of sound waves. All that’s needed is a couple of cardboard tubes, a balloon, and some sand. Both projects appeared in the August 1936 issue of Popular Science.

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