Science Fair Ideas: Fun With a Homemade Galvanometer

Eighty years ago, there was a war going on, but that didn’t stop young scientists on the home front from conducting experiments with the items available. If Junior’s science fair project is due tomorrow, he can take a cue, and whip together a great project from these ideas in the December 1942 issue of Popular Science.

Both experiments involve a galvanometer, and the magazine presupposes that young scientists know how to make one, because the instructions merely state to use “your homemade galvanometer.” But in case Junior doesn’t know, it’s easy enough. You just take a compass (a toy one from the dollar store will work just fine) and wrap a few turns of wire around it. The smallest of electric currents will cause the compass to move. If there’s a little extra time before the science fair, we’ve previously shown how to make a deluxe galvanometer.

In the first experiment, shown above, Junior can demonstrate that water, contrary to popular opinion, is an insulator. It’s only when a little bit of salt is added to the water that it starts to conduct electricity, and the compass moves. To accentuate the effect, we recommend starting with distilled water. And don’t worry about not being able to find the old-fashioned dry cell batteries. These experiments will work just as well with modern alkaline D cells, especially if you purchase battery holders for them.

The second experiment, shown below, shows how to make a thermocouple. Two pieces of wire–copper and iron (or steel)–are twisted together. When the twisted wires are put into a flame of a candle, the dissimilar metals produce an electric current, as shown by a movement of the compass. And as we always remind parents about experiments involving flames, don’t forget to give Junior a box of matches!

As with many of our projects, Junior is almost guaranteed to take home the blue ribbon, and the teacher won’t have a clue that the project was put off until the last minute.

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1937 Disco Ball

What we know as the “disco ball” has a long heritage, as shown by this depiction 85 years ago in the December 1937 issue of Popular Science. The magazine featured a number of ideas on what to do with a broken mirror, and assured readers that it needn’t signify seven years of bad luck.

The magazine noted that one use was to provide spectacular color effects for parties and dances. This was done by focusing colored spotlights on a mirror-covered globe. This was made by cementing small squares of mirror on a large ball or toy globe. This was attached to a spindle which could be spun by hand or with a small geared-down motor.

According to Wikipedia, what is now known as the disco ball dates back to 1917.

If you have a piece of mirror left over after making your disco ball, you can mystify your friends with the magic trick shown below:

1942 Miniature 2 Tube AC-DC Receiver

Eighty years ago this month, the December 1942 issue of Popular Science showed how to put together this two-tube AC-DC set. The miniature set used two midget tubes, types 9001 and 9002. The 9002 pentode served as a sensitive detector, and the 9001 triode was used as a rectifier.

The filaments were wired in series, and since they required a 600 ohm dropping resistor, not one but two “curtain burner” cords were used, wired in series.

With a short antenna lying along the floor, the set could pull in local stations with good selectivity. Out in the country with a 75 foot antenna, it boasted a range of 600 miles.

Tube Aging, 1947

These workers at Hytron‘s plant in Newburyport, Mass., are aging tubes to ensure long life. An incandescent lamp is wired in series with each tube element to limit current. This process of seasoning and degasifying the tubes ensures more uniform tubes.

The photo appeared on the cover of Radio News, December 1947.

Answers to Yesterday’s Quiz

As promised, here are the answers to yesterday’s quiz, from the December 1962 issue of Popular Electronics.

Electronics Numbers Quiz

Today’s quiz comes from the December 1962 issue of Popular Electronics. You have to match up the number associated with each diagram. Answers will appear here tomorrow.

1942 Expedient Chassis

The December 1942 issue of the British Practical Wireless carries this self-explanatory hint sent in to the magazine by one J.M. Firth of Beckenham. He noted that there was a great shortage of aluminum and sheet iron for making chasses for radios. Quite possibly to Mrs. Firth’s chagrin, he found a suitable replacement in the kitchen in the form of a tinplate baking tin. He noted that the pan would take solder easily.

1947 Five-Tube Radio Kit

There’s a reason why this young woman seems particularly cheerful about pulling in a station on her broadcast radio. It’s because she put the radio together herself from a kit.

The kit is described in the December 1947 issue of Popular Mechanics, and from the description, it sounds like an “All American Five” of the type manufactured by the millions. Curiously, though, the magazine doesn’t mention the source. If any of our readers can identify the brand of this kid, please let us know.

1922 British Frame Antenna & Variable Capacitor

A hundred years ago, this young British woman was pulling in some signals from her garden at 1276 Leeds Road, Bradford. She is undoubtedly the daughter of one Mr. C.R. Land, who constructed the set and sent the picture to Practical Wireless, where it appeared in the November 1922 issue.

The issue also showed an interesting method of constructing a variable capacitor, as shown below. The magazine noted that they could be expensive and difficult to make, but this version was relatively easy to construct at home. It consisted of two sheets of zinc carefully rolled into tubes and soldered together. The dielectric consisted of waxed paper.

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Science Fair Ideas: 1937 Electric Motor

If Junior wants to impress the judges at the science fair with attention to detail, skill with hand tools, and a generally spectacular project, then this 1985 project is sure to fit the bill. It’s a small electric motor, capable of providing some motive power to other projects.

The diagram shows old-fashioned dry cells, but modern alkaline D cells will work just as well, especially if you get battery holders to keep them in place.

The November 1937 issue of Popular Science shows the complete blueprints for the motor, but without too many verbose instructions. So as long as Junior can read a set a blueprints, the blue ribbon is pretty much assured.

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