E1 Electric Charge, Field and Potential

Topic

Electric charge is the property of matter that generates and responds to electromagnetic fields, and it is the central element of this entire section on fundamentals. Two charges attract or repel each other depending on their sign, with a force that increases as the charges grow larger and drops rapidly as they move further apart; conceptually, the electric field at a point in space is the force a test charge placed there would experience. In semiconductors, this same field—concentrated and intense at the junction between two regions with different doping levels—creates the potential barrier characteristic of a diode.

Electric potential—or voltage—is the energy available per unit of charge at a given point, and the potential difference between two points is precisely what drives charges to move, giving rise to electric current; without that difference, there is no physical reason for a charge to move in one direction rather than another. When work is done to move a charge within an electric field, that work depends both on the amount of charge being moved and on the potential difference it traverses.

Capacitors store energy precisely within the electric field that forms between their plates, and this stored energy grows much faster than the applied voltage itself: a moderate increase in charging voltage results in a much larger increase in the energy the capacitor can store.

For this reason, this module—which begins with a charge that generates and responds to fields—concludes by demonstrating that charge, field, potential, and stored energy are not four independent concepts but rather a single causal chain (charge creates the field, the field defines the potential, and the potential difference ultimately moves other charges) that serves as the conceptual foundation for all subsequent analysis of electronic circuits.

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