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The National MagLab is funded by the National Science Foundation and the State of Florida.

Parallel Wires

A pair of parallel wires serves to illustrate a principle that French scientist André-Marie Ampère was the first to comprehend.

Back in 1820, Frenchman André-Marie Ampère found through experimentation that the magnetic fields created by parallel current-carrying wires interact with one another, as demonstrated in this tutorial. He examined the difference in the interaction based on which way current was flowing in the parallel wires.


  1. Take a look at the circuit, which includes two parallel straight wires, in red.
  2. The circuit can be arranged as a series or parallel.
  3. Click “run” to see what happens when the wires are linked in a series circuit
  4. See how the current, running in opposing directions in those red wires, creates magnetic fields that oppose each other, shown in blue. This makes the wires repel one another
  5. Now click "parallel circuit" to see what happens when the layout is adjusted.
  6. Note how, as current is flowing in the same direction, the wires are now attracted to one another because their magnetic fields, shown in blue, are opposing one another, and opposites attract.

The difference between the series circuit and parallel circuit can be explained by the right hand rule, which helps visualize how a magnetic field (depicted by the blue field lines above) around a wire travels. Extend your thumb in the direction of the conventional current, then allow your fingers to curve: The magnetic field circling the wire travels in the direction that your curved fingers are pointing. So if you have two current-carrying, parallel wires with magnetic fields circling around them in the same direction, they will attract each other, as shown in the tutorial; at the point at which their respective magnetic fields intersect, they are traveling in opposite directions, and opposites attract. Similarly, if you have two parallel wires with current traveling in opposite directions, as you do in the series circuit, then the magnetic fields of the two wires will be traveling in the same direction at the point at which they intersect, and therefore repel each other.