TABLE OF CONTENTS Electric current is the flow of electrically charged particles along a wire. (The particles that flow are usually electrons, which by convention have a negative charge as a consequence of Benjamin Franklin guessing wrong; therefore the direction of current flow is usually opposite the direction in which the particles actually move. Sorry.) A resistor is a device that doesn't store electrical charges, but merely resists their flow. Electrical engineering starts with Ohm's law: the voltage across a resistor is proportional to the current flowing through it. In mathematical terms:
| (A3.1) |  |
where I is the current, R the resistance, and V the voltage. Electrical current is usually carried in thin wires, and generally returns to where it started to form a circuit. We can draw a simplified picture of an electrical circuit, using line segments for wires, a circle to symbolize a voltage source (like a battery or generator), and a squiggly line to indicate a resistor. This is known as a schematic diagram, or just schematic for short. The schematic for a simple circuit containing only a resistor and a voltage source is shown in Figure A3.1. The figure also shows a ground symbol. Ground is just the location in the circuit where the voltage is defined to be equal to 0. The voltage along a wire is constant, so the voltage on all the wires directly connected to ground is 0. The voltage source creates a voltage...
