HOW TO CONSTRUCT A COMPASS GALVANOMETER

OBJECT:

How to construct a Compass Galvanometer. Used to measure small currents.

MATERIALS:

SAFETY FIRST: I would suggest that your parents do any cutting, plastic is a little difficult to cut, and there is a possibility of injury to small fingers.

One large clear plastic soda bottle, Safety scissors, Pliers, Compass, Mini alligator clips with leads Radio Shack (RS) # 278-1156, A spool of magnetic wire (thin copper wire, coated with shellac) # 28, (RS #) Magnet wire # 278-1345, A small piece of fine sand paper, Large safety pin, Small socket and small bulb (RS # 272-359 or 272-360), A one cell D battery, preferable an almost dead or very little life left, Stapler.

PROCEDURE:

1. Use a clean clear (preferably no color) large plastic soda bottle, to serve as you book jacket. Remove the plastic attached cover from the bottle, then flatten one side, and then with safety scissors, make a SMALL incision.

2. Next proceed to cut up, and then down, ( See diagram ) the length of the cut should be about five inches. Cut around the top area, then cut around the bottom area. It will take some effort, because the plastic bottle will tend to curl.

3. Try your best to flatten the curled plastic, just about in half, with your hands, then repeat the bend with a pair of good pliers. Next use a marker or just use your judgement to make another bend HALF an INCH over, from this bend, first using your hands, then repeating it with a pair of good pliers. You will have to fight with your curled plastic. Now that you have your two sharp corners, you may now trim the plastic so that it measures 4 and 1/2 inches high, and 3 inches wide each side.

4. Put staples in, at the open ends, ( two ) to make the cover more rigid as indicated in the diagram. Make a NOTCH in the middle of your cover, about one half inch wide and 1/4 inch deep, coming to a point.

5. Make four Pin holes near the back edge of the book cover. All the holes should be about one eight of an inch from the back edge of the book cover and the first two holes should be about one inch apart opposite the NOTCH. The last two holes should be located at the ends or edges of the book cover.

6. Take your # 28 Magnet wire (Any THIN copper wire should do, as long as it has a shellac coating for insulation.) Thread your thin ( IN ) wire through the hole above the Compass position, then thread it OUT at the top hole, such that you have about ONE FOOT of working wire. To make sure that the wire will not slip, you may want to thread it again through the same last hole (loop it twice) or make another hole (right next to this one) if the original one is to small to pass the wire through again . Using a plastic CAP, about the size of the compass, substitute it in place of the compass. Now start wrapping your wire around the plastic book cover, going away from the hole and towards the notch. You should have at least 28 turns, however, to increase sensitivity of the instrument, you may double it, just remember the more turns that you have the more sensitive the instrument should be. When you are finished wrapping your wire, leave about a good ONE FOOT over to finish the job. Thread this end wire IN ( DOWN ) through the second hole under the compass position, then thread it OUT ( UP ) the end hole. Do you know how to secure the wire so that it does not slip?

7. Since the fine wire has an insulation of shellac over it, you have to remove the shellac, by using a small piece of about one inch in size, of fine sand paper. Hold the wire in your LEFT hand, with the other hand (RIGHT) hold your fine sand paper that has now been folded in half. Place you wire ( about an ONE INCH in length) between the two halves of sand paper, squeezing the sand paper halves with your thumb and index finger, and pull sand paper toward the end of the wire until the wire is free. You should be able to see some bare copper wire exposed, if not, repeat the process, until you see the bare copper wire. If the wire is very thin, you have to be extra careful not to break the wire, this will take practice, so you may want to practice on a piece of wire before you continue. Once you get the hang of it, rotate the wire that you held in your left hand, and repeat the process of removing the shellac from the wire. You will have to rotate the wire several times, to remove all the shellac from the wire. Be sure to do this for the other end as well!

8. Using your mini alligator clips with leads, make your connection as shown in the diagram. Do not insert the miniature bulb, until ready for testing. Reason for using a miniature bulb and socket, it will act as a limiting resistor, to prevent any over load for the circuit. In other words prevent over heating and burning out the battery. If you are not using mini alligator clips and leads then you may try the following; Using Bell ( Thin copper wire (small gauge) with plastic cover on it. ) wire for your hook up wire, carefully remove about half an inch of insulation, so that the bare copper wire is exposed. The safest thing to use, is a wire stripper, the next safest, thing to use is a pair of old nail clippers, but you have to remove the handle that you squeeze or push down on, so that there is nothing attached to the clippers! Holding the bare clippers in you RIGHT HAND, with your LEFT HAND insert about half an inch of bell wire into the side of the clippers, squeezing with your thumb and index finger. The idea is to cut through the plastic covering only, then relax the clippers and rotate the wire that is held in your left hand 90°. Then squeeze the clippers again, trying to cut through the plastic covering, and pull on the wire, and see if you are successful in removing the plastic cover. Again, you may have to practice with a piece of Bell wire before you get the hand of it. To make your connection to the battery holder, use small nuts and bolts to fasten your bell wire to the battery holder, which has two paper clips.

9. Remove the plastic cap and insert your compass into the plastic cover. If you will be using your newly made NEEDLE COMPASS, you should NOT use the small Styrofoam cup. You should find a PLASTIC BOTTLE CAP large enough to accommodate the NEEDLE. Like the cap from one gallon Ocean Spray plastic bottle or similar to that size. Fill cap halfway with water, place your needle inside, be very careful not spill the water. The action with the needle compass will be much slower, so keep that in mind. Make sure the NOTCH is facing NORTH, which means the Needle compass is parallel to the wire coil. Insert your bulb and watch the action begin.

10. Observe where the compass is pointing to, then reverse the plus and minus on your Galvanometer, and see if the direction has changed.

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