Electron Flow Theory

Instructor: Laura Foist

Laura has a Masters of Science in Food Science and Human Nutrition and has taught college Science.

In this lesson, learn about electric currents and the history of how scientists understood currents. Also, explore the electron flow theory and how the electron flow theory applies to currents. Updated: 09/20/2022

Electron Flow and Currents

When electricity was first discovered, it was a power and force that almost seemed magical to everyone. Even the scientists who studied electricity didn't fully understand what was occurring. One of the aspects of electricity that took a while to understand was how molecules moved in electrical currents.

In the 16th century, William Gilbert first discovered that there were positive and negative charges. And from this discovery, scientists began to understand currents a bit better. They realized that these opposite charges would cause a flow of ions, which was responsible for the currents generating electricity.

Think of a magnet with positive and negative ends. When placed close to each other, it will cause the magnets to move on their own towards each other or away from each other, depending on if opposite charges or the same charges are facing each other. The positive and negative charges in a flow of electricity work the same way. Negative charges want to leave the source of the negative charges (the cathode) towards the positive charge (the anode).

Image of battery, with current showing flow from positive to negative caption=

Some early experiments with these positive and negative charges made it appear that the charges flowed from the positive source to the negative source. It was believed that the positively charged ions were what flowed through the wires towards the negative source to create the electrical current. This theory that electrical current is made of positive ions is called the conventional current theory.

Electron Flow Theory

As cathodes and anodes were made and studied, J.J. Thomson discovered that electrons originate at the cathode and flow towards the anode. This discovery meant that the flow of current wasn't a flow of positively charged ions; instead, the flow is made of negatively charged ions. This theory that electrical current is made up of negative ions is called electron flow theory

J. J. Thomson came up with electron flow theory
Image of J J Thomson

This means the negative ions start at the cathode where they are made, then flow towards the positively charged anode. If the negative side of a magnet was set next to the positive side of a magnet, where the positive side was bolted down so it wouldn't move, the magnet with the negative charge would move towards the positive magnet.

As electrons are generated in the cathode, they quickly move towards the anode. Electrons continue to generate and continue to move towards the anode. This continual movement of electrons is what creates a current, which is what makes electricity work in the wires all around us.

Electron Flow Theory vs Conventional Current

Today, it is generally accepted that the electron flow theory correctly describes how electrical current works. But the conventional current theory continues to be used, and when looking at diagrams of currents, it is often shown as though the current is moving from the positive to the negative terminals. Why does the conventional current theory continue to be used?

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