What is the difference between Conventional Current and Electron Flow?
Conventional Current and Electron flow are two different standards for designing and interpreting electrical schematics. The topic sometimes confuses new students of the study of electricity, and many wonder which format to learn.
Both models describe the direction electricity flows through a circuit. Conventional Current assumes that electricity flows from positive to negative, and Electron Flow assumes that electricity flows from negative to positive. Both models can be used to analyze circuits, as long as only one model is used at a time. Even the analysis of a very complicated circuit will yield the same results under both systems.
There are two major differences to keep track of while designing an electrical schematic, the first of which involves diodes and is shown in the diagram below. The diagram is correct for both flow models, notice that a diode points from positive to negative regardless of the direction chosen. If the diode were removed from the circuit, the battery terminals could be switched and electricity would still flow. This is because electricity can flow through a resistor in both directions (this characteristic is sometimes described as non-polar). Electricity will only flow through a diode (which is polar), in one direction. If the diode direction is reversed in the diagram below, electricity will not flow.
The second difference between Electron Flow and Conventional Current is the direction of magnetic fields created by current. All current produces a magnetic field; in Electron Flow, if you hold a current carrying wire with your left-hand and your thumb pointing in the direction of the current, your fingers will wrap around the wire in the direction of the magnetic field. Similarly, a right-hand rule exists for determining the direction of the magnetic field under Conventional Current. The diagram below shows that the direction of the magnetic field is the same for both the left-hand and right-hand methods.
Which direction does current actually flow, and why do two systems exist?
Electric current occurs when a difference in positive and negative charges is allowed to neutralize. A positive charge can exist in the form of a positive ion (an atom missing an electron), and a negative charge can exist as a lone electron, or a negative ion. In most circuits electric current exists in the form of electrons traveling through a conductor to a source of positive charge. Electron Flow is the correct model describing the reality of what occurs in a circuit.
In the mid to late 18th century, Benjamin Franklin theorized that positive and negative electric charges existed. He guessed that electricity traveled from positive charge to negative, and was wrong. In 1897 British physicist Sir Joseph J. Thomson proved that electric current is actually the flow of electrons. By that time Conventional Current was so ingrained into the literature describing electricity that both models for current direction continue to be used.
Which model should I learn, and which model is used by professionals?
It helps to understand that both current models exist; when reading an article or book about electricity, it sometimes helps to determine which model text is written with. Usually this is stated in the preface of a book, or at the beginning of an article where current direction might be relevent.
In general, the military uses Electron Flow, and electrical engineers and scientists use Conventional Current. It is usually necessary to recognize which standard is used when entering a career involving electricity.