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Direction of Direct Current (DC) Electricity

by Ron Kurtus (14 November 2019)

By convention, the direction of direct current (DC) electricity in a DC circuit goes from the positive (+) terminal of the source towards the negative (−). That is: plus to minus. However, the movement of electrons in a DC circuit is in the opposite direction than that of the current.

The historical background started with designating the electric charges as plus and minus and then naming the ends of a battery as positive (+) and negative (−). Then after the electron was discovered, it was found that the motion of those negative charges are in the opposite direction of the electric current.

This seems illogical and can be confusing to most people, but the directions are just something that should be remembered.

Questions you may have include:

This lesson will answer those questions. Useful tool: Units Conversion



Ben Franklin names electric charges

Around 1750, after studying static electricity, Benjamin Franklin called one type of electricity as "positive" and the other as "negative".

He thought that positive electricity signified an excess of the "electric fluid" over the usual amount, while the other kind was "negative", signifying a slight deficiency.

Volta invents the electric battery

In 1800, Alessandro Volta invented the electric battery, which came to be known as the voltaic pile. The voltaic pile consisted of pairs of copper and zinc discs piled on top of each other, separated by a layer of cloth or cardboard soaked in brine.

One end of the battery was assigned as positive and the other as negative, according to the metals used. Scientists then naturally assigned the direction of the flow of current to be from (+) to (−).

Electrons move in opposite direction

The electron was discovered by J. J. Thomson in 1897 when he was studying the properties of cathode ray.

It was then realized that in metal wires the electrons were the ones that carried the current, moving in exactly the opposite direction of the designated current. Unfortunately, it was much too late to change Franklin's naming convention.

Knowing that the actual charge carriers in wires are negatively charged electrons may make this convention seem a bit odd and outdated. Nonetheless, it is the convention that is used worldwide and one that a student of physics can easily become accustomed.

Summary

By convention, the direction of direct current (DC) electricity in a DC circuit goes from the positive (+) terminal of the source towards the negative (−). The historical background started with designating the electric charges as plus and minus and then naming the ends of a battery as positive (+) and negative (−).

After the electron was discovered, it was found that the motion of those negative charges are in the opposite direction of the electric current.


Study the history of discovery


Resources and references

Ron Kurtus' Credentials

Websites

The Direction Assigned to Electric Currents - NASA education archive

History of the Battery - Wikipedia

Discovery of electrons, protons and neutrons - Open Teaching Project

DC and AC Electricity Resources

Physics Resources

Books

Top-rated books on DC Electricity

Top-rated books on Basic Circuit Design

Basic Electricity by Bureau of Naval Personnel; Dover Pubns; (1970) $14.95 - Provides thorough coverage of the basic theory of electricity and its applications

Basic Electricity and DC Circuits by Charles Dale, Prompt (1995) $54.95 - Large book with basic concepts to harness and control electricity


Questions and comments

Do you have any questions, comments, or opinions on this subject? If so, send an email with your feedback. I will try to get back to you as soon as possible.


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Direction of Direct Current (DC) Electricity




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