What You Do:
Galvanometers are used to detect electrical current. You can make your own using wire and a compass. Use 3-4 feet of thin insulated wire. Wrap the wire tightly several times around the compass, leaving about eight inches of wire at each end.
Now strip about an inch of the plastic insulation off each end of the wire, leaving bare copper wire exposed.
Next, press the bare ends of the wire to a C- or D-cell battery. Only leave the circuit connected for 2-3 seconds, just long enough to see the needle start spinning. The current flow will heat the battery and wires if you leave them connected for more than a few seconds.
The current flowing through the circuit produces an electromagnetic field, which makes the magnetized compass needle try to align with it as the current moves through the circuit. If you change the direction of the current (by turning the battery around so the negative terminal will connect to the other end of the wire), then you should also be able to see a change in the direction that the compass needle moves. Try coiling your wire tighter, or make more coils around the compass. Does it make a difference in how much or how fast the compass needle moves?
This homemade galvanometer is not a quantifiable measure of current – it shows you whether electrical current is flowing, and the direction it’s flowing in, but not how many amps are being produced.
Try testing for current from other sources. For example, stick two electrodes (copper and zinc) into half of a lemon, and then press one of the galvanometer end wires to each electrode. Is there any current flowing? Can you tell which direction it’s flowing? Did the lemon battery make the compass needle move more or less than when you hooked it to a regular battery?