10.0 CURRENT ELECTRICITY

This chapter marks the transition from static electricity (charges at rest) to current electricity (charges in motion). Here we learn how to generate a steady flow of charge, control it, and understand the components that make up electric circuits. This knowledge is the foundation for all of modern electronics and electrical engineering.

10.1 SIMPLE ELECTRIC CIRCUITS

An electric circuit is a closed path through which electric current can flow. It consists of a source of energy (like a cell) and components (like bulbs, switches) connected by conducting wires.

10.1.1 Circuit Components and Symbols

To draw circuits easily, we use standard symbols. Here are the most important ones:

• Cell: A long line (positive terminal) and a short thick line (negative terminal) drawn parallel. Represents a single electrical energy source.
• Battery: Two or more cells joined together. Drawn as multiple cell symbols.
• Switch: Represented as a break in the line with a movable contact. When closed, the circuit is complete; when open, it's incomplete.
• Bulb (Lamp): A circle with a cross inside (or a circle with a filament loop). Converts electrical energy into light and heat.
• Resistor: A zig-zag line (or a rectangle). It opposes the flow of current.
• Ammeter: A circle with the letter 'A' inside. Measures current and is always connected in series.