Electric Charge and Fields

Electric Charge & Coulomb's Law

All electronics rest on electric charge, coming in positive and negative signs. The fundamental rule: like charges repel, opposite charges attract. Charge is conserved (never created or destroyed) and quantized (multiples of $e$).

The force between two point charges is given by Coulomb's law:

$$F = k\frac{q_1 q_2}{r^2}$$

Common pitfall: Coulomb's force falls off as $1/r^2$. Doubling the distance cuts the force to a quarter, not a half. Never confuse like repulsion with attraction.

Fields & Voltage

Rather than charges reaching across empty space, physics uses the electric field $E$: a charge creates a field, and another charge placed there feels a force $F = qE$. The field is force per unit charge, pointing away from positive and toward negative.

Voltage (electric potential) is potential energy per unit charge, the electrical height driving charges to move. A charge moves from high to low potential like a ball rolling downhill.

Common pitfall: Do not confuse force ($F$), field ($E$), and voltage. Voltage difference is what pushes current through a circuit.