How to Build an Ammeter
An ammeter measures the electrical current in a circuit. The earliest design is known as a moving-coil ammeter and contains a coil of wire that moves in a magnetic field. This movement is then transferred to a needle that moves in proportion to the electrical current. A similar design called a moving-iron ammeter uses a piece of iron that moves within a coil of wire in response to an electromagnetic field. A moving-iron ammeter can be built as a school project.
Things You'll Need
- 2 alligator-clip leads
- 2 small disk magnets
- AA battery
- Aluminum foil, 2.5-cm square
- Corrugated cardboard, 10-cm square
- Hot melt glue
- Pushpins
- Sandpaper
- Thread
- Toilet-paper tube
- Utility knife
Instructions
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1
Cut off a 4-cm section of the toilet-paper tube and wind at least 100 coils of magnet wire around the tube. Be sure there's at least 10 cm of wire remaining on each end. Secure the coil on the tube with hot melt glue. Attach the toilet-paper tube to the cardboard base with hot melt glue and remove the insulation from the ends of the magnet wire with the sandpaper.
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2
Form a loop with one end of the magnet wire and twist it several times. Fold aluminum foil around the loop several times to form a rectangle that measures about 2.5 cm by 1 cm. Secure this aluminum pad to the cardboard with a pushpin. Do this with the other end of the wire as well and mark one of the ends with a "+" sign.
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3
Cut a short slit on top of the toilet-paper tube on each side of the coil. Place a 10-cm length of thread between the two disk magnets and put them together so the magnets hold the thread in place.
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4
Pass each end of the thread through one of the slits and take up enough slack so the magnets are suspended in the middle of the tube. Tie the ends of the thread together.
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5
Rotate the entire assembly until the magnets align so that only their edges are visible when you look down the tube. This is the ammeter's zero position. Connect the positive terminal of the battery to the positive terminal of the ammeter and the negative terminal of the battery to the other terminal of the ammeter. You should see the magnets rotate in response to the electrical current.
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