Current Detector (Galvanometer)
The objective of this experiment is to demonstrate the relationship
between electricity and magnetism. In this experiment we will also show
how to create and detect magnetic fields.
about 8 feet of insulated wire (18-24 gauge)
metal sewing needle
3 feet of thread
6 volt battery
a small strip of paper
How To Build It
Magnetize the needle by rubbing one side of the permanent magnet against
it about 30 times in the same direction. Cut the paper into a small arrow.
Stick the needle lengthwise into the paper arrow.
Now put some thread through the top edge as shown.
Using the wire, make a loop about three inches in diameter. Continue to
wrap the wire in the same pattern as the original loop until you have a
coil of about five loops. You should keep some wire free on both ends.
Use the thread to tie the wires together. Now tie the thread attached to
the paper to the top of the loop. The paper with the needle should hang
freely inside the middle of the wire loop.
Attach one end of the wire to the positive terminal of the battery,
and the other wire end to the negative terminal. Notice what happens to
the paper arrow. It should turn and point directly out from the middle
of the loop. Now turn the loop. Notice that the arrow follows the loop
and continues to point directly out of the loop.
If your arrow does not seem to be affected when you attach the loop
ends to the battery, try the following:
Questions for Thought
- Make sure the wires are snugly connected to the battery.
- Make sure that the needle is sufficiently magnetized. You might want
to pull it out and stroke the magnet across it several more times.
Make sure that you stroke only one pole of the magnet in only one direction
across the needle. Do not simply rub the magnet back and forth across the
- Try increasing the number of loops of wire.
- Replace the battery. Extended continual use of a battery can drain
its power due to the low resistance of the wire.
- Why did the arrow turn out from the loop?
- ANSWER: Current through a wire produces a magnetic field around the
wire. When current is run through a loop, it produces a magnetic field
inside of the loop. Since the needle is magnetized, it tries to align itself
with the magnetic field produced by the current in the loop. This is the
same way a compass works. The needle inside of a compass is magnetized.
That needle tries to align itself with the magnetic field produced by the
- What would happen if we change the direction of the current?
- ANSWER: The needle would point in the opposite direction. This is because
the direction of the magnetic field is dependent on the direction of the
current. The direction can be "predicted" using the right-hand-rule.
That is, by wrapping your right hand around the wire with the thumb in
the direction of the current flow(from the positive to the negative battery
terminal), the magnetic field is curled in the direction of the remaining
four fingers of the right hand.
Several books explain this same experiment. They usually use a working
compass, and simply wrap the wire into loops around the compass. The only
difference is that here, we make our own "compass." This is because a needle
is much easier to find and much less expensive than a compass.
- Science Activities With Simple Things by
Howard R. Munson, Ed. D. Fearon-Pitman Publishers, Inc. 1962. p. 45.
- The Magic of Electricity by Sam Rosenfeld. Lothrop, Lee and
Shepard, Inc. 1963. p. 67.
Last Updated: June 21, 2002
Original Page Development by: Matt Dayley and Keith Holbert
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