Final answer:
The conventional theory of current flow defines current as moving from the positive terminal to the negative terminal in a circuit, a concept dating back to Benjamin Franklin.
Step-by-step explanation:
The conventional theory of current flow is rooted in historical conventions dating back to the 1700s. Originally defined by American scientist and statesman Benjamin Franklin, conventional current is considered to flow from the positive to the negative terminal in a circuit. This definition presumes that positive charges move in the direction of the electric field created by a voltage source. Even though, in many cases such as in metal wires, it is actually the negative charges (electrons) that move, and they move in the direction opposite to the conventional current. Similarly, in ionic solutions, both positive and negative charges move, contributing to the overall flow of electricity.
In essence, conventional current represents the direction that positive charges would flow, even though the actual charge carriers might be negative. It is consistent throughout a circuit, just as shown in Figure 20.3, where the current at all points is the same if there are no losses, due to the conservation of charge. This concept is not just a theoretical principle but also applies to practical devices such as the Van de Graaff generator that can generate pure positive currents composed of protons, and the historical Tevatron Accelerator at Fermilab which propelled protons and antiprotons in opposite directions.
Today, despite the knowledge that electrons carry the current in metals, the notion of conventional current remains widely used for the purpose of circuit analysis and electrical engineering design. It simplifies the description of current flow and electrical circuit behavior.