Resistance: Does the Thickness of a Wire Affect the Flow of an Electric Circuit?

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Author: Janice VanCleave


Does the thickness of a wire affect the flow of an electric circuit?


  • 2 8-inch (20-cm) foil strips
  • 3 new, clean pennies
  • duct tape
  • size D battery
  • short, wide rubber band
  • flashlight bulb
  • coarse steel wool
  • large steel paper clip


  1. Wrap the end of one foil strip around the penny, and tape the foil-wrapped penny to the negative terminal of the battery.
  2. Tape the second foil strip to the positive terminal of the battery.
  3. Stretch the rubber band around the battery to hold the coin and strips tightly against the battery ends.
  4. Take the free end of the foil strip that is attached to the negative terminal of the battery and twist it tightly around the base of the bulb.
  5. Pull a single strand out of the steel wool, and tape one end to the face of a penny.
  6. Pull the steel strand taut, and tape its free end to the third penny so that 1 inch (2.5 cm) of the steel strand is stretched between the two coins. Cut off any excess.
  7. Touch the bottom of the bulb to one of the coins, and touch the free end of the foil strip attached to the positive terminal of the battery to the other coin.
  8. Observe the brightness of the bulb.
  9. Resistance

  10. Replace the strand of steel wool with a straightened paper clip. Let the ends of the paper clip extend past the coins so that 1 inch (2.5 cm) of the metal lies between the coins.
  11. Repeat steps 4 through 7.


The light glows much more brightly with the thicker wire from the paper clip.


The steel wool strand and the steel paper clip both allow electric current to move through them; thus, both are conductors. The brightness of the bulb indicates that the thicker steel paper-clip wire has more electric current going through it than the thin steel wire. The measure of how difficult it is for an electric current to move through a material is its electrical resistance. The thinner the wire, the greater its resistance and the less electric current going through it. The unit of measuring electrical resistance is the ohm.

Let's Explore

  1. Does the length of the wire affect the results? Repeat the experiment twice, first using shorter lengths of wire, and then increasing the wire lengths.
  2. Does the type of material linking the coins affect the result? Repeat the previous experiment using different materials such as rubber bands, strands of hair, and copper wire. Science Fair Hint: Display the different materials used in each experiment, along with diagrams showing light bulbs and indicating their brightness. Label the materials as low, medium, high, and very high resistance. The materials with very high resistance will be those that completely oppose the flow of electricity so that the bulb does not glow.
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