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Make a Galvanometer

A Galvanometer is an extremely sensitive voltage detector. A very simple yet still sensitive galvanometer can be constructed using an ordinary compass.

The best compass to use is a good cheap one. Don't use nice liquid filled hiking ones, as the liquid suppresses the movement of the needle, decreasing sensitivity. Don't use 50 cent compasses either. Mine cost around $6 US. The requirements of a good compass are that it spin freely and not be too sensitive to being tilted.

The minimum materials required are a spool of 30 gauge magnet wire, a compass and some electrical tape. To build one as shown, you also need a hot glue gun (or other glue) and two 1 1/2" brass bolts of the size known as 8/32s, with washers and nuts. It is important to use brass or nonferrous fasteners to prevent magnetic interference. You will also need a piece of wood or something to mount it all on. I used a 1"x4"x6" piece of pine.

Cut two small pieces of electrical tape, and stick them somewhere handy. Take the wire and the compass, and use one piece of tape to hold the wire to the back of the compass. Leave at least 6" of wire hanging off the end. Wrap a bunch of turns on the compass, the number isn't critical, but should be between 30 and 50. Use the other piece of tape to secure the end of the wire, then cut the end to match the other in length.

If you aren't going to mount your galvanometer, strip the ends of the wires with some fine sandpaper, and you're done!

If you are going to mount it, drill holes big enough to push the bolts through at both ends. Poke the bolts through, and tap the heads flush with the wood using a hammer. Check where you want the compass to be mounted, then put a splort of hot glue on the spot. Put the compass in place, squish it down a little and wait a few minutes for it to dry.

Cut the wires so that they are about 1" longer than needed to reach the bolt. Strip the last inch of the wire and wrap it onto the base of the bolt. When tightening the nut, be careful not to break the wire. If you do you'll have to cry, stick the whole thing in the freezer for a while and then try to pry the compass off.

How does it work? As noted elsewhere on the site, whenever an electrical current flows, a magnetic field is produced. So when an electrical current flows through the wire wrapped around the compass, a magnetic field is made. This interacts with the magnet needle of the compass, causing it to move.

Check the HERE for experiments using a galvanometer.