Circuit Symbols, Schematics & Current Flow (Foundations of Circuits)
To represent electric circuits clearly and conveniently, standard electrical schematic symbols are used universally across science and engineering.
1. Standard Electrical Components & Symbols
| Component | Function / Feature | Schematic Symbol Description |
|---|---|---|
| Electric Cell | Source of electric potential energy | One long thin vertical line ($+$ terminal) and one short thick vertical line ($-$ terminal) |
| Battery | Two or more cells connected in series ($+$ to $-$) | Multiple alternating long-thin and short-thick lines connected end-to-end |
| Switch (ON / Closed) | Completes the conductive circuit loop | Line bridging both terminal contact circles |
| Switch (OFF / Open) | Creates an intentional break in the loop | Line tilted upward away from one contact circle |
| Electric Bulb | Converts electrical energy into light | Circle containing a looping curl representing the tungsten filament |
| Connecting Wire | Low-resistance path for electric charge | Straight horizontal and vertical lines |
2. Closed vs Open Circuits
- Closed Circuit: The conductive path is complete and uninterrupted from the positive terminal of the cell, through the load (bulb), back to the negative terminal. Current flows smoothly, and the bulb illuminates.
- Open Circuit: There is a physical break or gap at any point in the circuit (e.g., switch is in the OFF position, or the bulb filament is broken/fused). Current stops flowing immediately, and the bulb does not glow.
3. Direction of Electric Current
By international scientific convention, electric current is considered to flow from the positive ($+$) terminal to the negative ($-$) terminal through the external circuit.