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.

The first person to discover evidence that electricity and magnetism are related phenomena was Hans Christian Ørsted. In the midst of a lecture on electricity, Ørsted noticed that a wire carrying current was able to deflect a compass needle. Unable to develop a plausible explanation, Ørsted published his findings in 1820. This news sent shockwaves through the scientific community and instigated numerous investigations into the matter. One of the scientists who immediately began to expand upon Ørsted’s work was Frenchman André-Marie Ampère. Soon after, Ampère found that the magnetic fields created by parallel current-carrying wires interact with one another, as demonstrated in this tutorial.

The direct current circuit in this tutorial includes two parallel straight wires (in red). These wires can be arranged in a series circuit, as they are when this tutorial first opens, or in a parallel circuit. In the series circuit arrangement, the parallel wires are linked by a connecting wire into a circuit that allows current along a single path. As a result, the current travels one way down one wire, and in the opposite direction down the second wire.

You can change this to a parallel circuit by clicking on the radio button; in this scenario, the current forks when it reaches the parallel wires; some current goes down one of the wires, the rest down the second. The current down both wires travels in the same direction.

Watch how the parallel wires behave in each of these set-ups. When either circuit type is selected, the Knife Switch can be lowered to complete the circuit by clicking either the switch itself or the blue Run button. Notice a stream of yellow electrons traveling through the circuit; flowing (as they always do) from negative to positive – opposite the direction of conventional current. To halt the flow of current, click on the red Stop button or the knife switch. Clicking the blue Pause button will let you examine the process in mid-stream.

As you can see, the wires in the series circuit repel one another, while the wires in the parallel circuit attract one another.

This is 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 (represented by your thumb) 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.

Ampère was able to mathematically describe this type of magnetic force between electric currents, formulating what is known as Ampère’s law.

Last modified on 8 November 2021
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