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Using a Magnet as an Electrical Current Detector

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Areas of Science
Time Required
Short (2-5 days)
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An electric current produces a magnetic field. You can take advantage of this fact to make a simple apparatus to test the electrical conductivity of various materials, including both solids and liquids. The detector consists of a coil of wire, with a magnetic compass inside it. You connect one end of the coil to a D-cell battery. The other end of the coil is connected to whatever material you are testing, and the material, in turn, is connected to the other end of the D-cell. In other words, the coil is connected in series with whatever material you are testing. To make the coil, use about 10 m (33 feet) of insulated, 24 gauge wire. You can use a roll of duct tape (or something similar) as the form for wrapping the coil. Leave 30 cm (about a foot) of wire loose at each end of the coil for connecting it up to your circuit. Strip off about 1 cm of insulation from each end. Stand the coil on its side (you can prop it up with clay to keep it from rolling). Fold a piece of cardboard to make a platform for the magnetic compass at the center of the coil. Use insulated wires with alligator clips to connect the coil to the rest of your circuit. You can make connectors for a D-cell battery by taping a paper clip to each end and resting the battery on its side. To test conductivity of a liquid, use paper clips taped on opposite sides of a plastic cup as connectors. When testing different materials, connect the battery only long enough to see the compass needle movement, so the battery will last longer. Other ideas you can explore: Learn about the "right hand rule" for magnetic fields produced by electrical current. Does the compass needle move as expected according to the right hand rule? Learn about Ohm's law and try your detector in circuits with various resistors. Is there a relationship between how far the compass needle moves and the current flow in the circuit? (Math, 1981, 13; Gardner, 2004, 80-85)


  • Gardner, R., 2004. Electricity and Magnetism Science Fair Projects: Using Batteries, Balloons, and Other Hair-Raising Stuff. Berkeley Heights, NJ: Enslow Publishers.
  • Math, I., 1981. Wires and Watts: Understanding and Using Electricity. New York, NY: Charles Scribner's Sons.
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MLA Style

Science Buddies Staff. "Using a Magnet as an Electrical Current Detector." Science Buddies, 28 July 2017, https://www.sciencebuddies.org/science-fair-projects/project-ideas/Elec_p044/electricity-electronics/using-a-magnet-as-an-electrical-current-detector. Accessed 6 June 2023.

APA Style

Science Buddies Staff. (2017, July 28). Using a Magnet as an Electrical Current Detector. Retrieved from https://www.sciencebuddies.org/science-fair-projects/project-ideas/Elec_p044/electricity-electronics/using-a-magnet-as-an-electrical-current-detector

Last edit date: 2017-07-28
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