Meet the Components

Why Learn Components First?

Before we dive into the math of electronics, you need to recognise the physical parts and their symbols. Every circuit — from a flashlight to a smartphone — is built from a handful of standard components. Once you know what they look like and what they do, reading and building circuits becomes much easier.

Reading a Schematic Diagram

A schematic diagram is a map of a circuit. Instead of drawing realistic pictures of every part, engineers use standardised symbols connected by lines (wires). Learning to read schematics is like learning an alphabet — once you know the symbols, you can understand any circuit diagram. Lines represent wires (conductors), and the special symbols represent components.

Batteries & Voltage Sources

A battery is a device that provides electrical energy by converting chemical energy into a voltage difference between its two terminals. The longer line in the schematic symbol represents the positive (+) terminal; the shorter, thicker line represents the negative (−) terminal. Common household batteries include 1.5 V AA cells and 9 V rectangular batteries.

Wires & Conductors

Wires are simple conductors that carry current between components. In a schematic they are drawn as straight lines. Where two wires connect there is a filled dot (junction). Where two wires cross without connecting, one line is drawn with a small bump or the crossing is left unmarked (no dot).

Resistors

A resistor is a component specifically designed to resist the flow of current by a predictable, fixed amount. Resistance is measured in Ohms (Ω). Resistors are used everywhere: to limit current, divide voltage, set bias points, and protect other components.

Types of Resistors

Not all resistors are made the same way. The construction affects their precision, noise, power handling, and cost:

• •Carbon-film resistor — Cheap and common, used in general hobby circuits. They have coloured bands painted on the body that encode the resistance value.
• •Metal-film resistor — More precise and stable than carbon-film. Preferred when accuracy matters (e.g., audio circuits, measurement equipment).
• •Wire-wound resistor — Made by winding resistance wire around a ceramic core. Excellent for high-power applications (5 W and above) because they can dissipate a lot of heat.
• •Surface-mount (SMD) resistor — Tiny rectangular chips soldered directly to a circuit board. Used in almost all modern electronics because of their small size.

Switches

A switch controls whether current can flow through a circuit by opening or closing a gap in the conductor path. When the switch is closed (ON), the circuit is complete and current flows. When the switch is open (OFF), the path is broken and current stops. Toggle switches, push-buttons, and relays are all types of switches.

Fuses

A fuse is a safety device placed in series with a circuit. It contains a thin piece of wire that melts (blows) when too much current flows, breaking the circuit and protecting components from damage. Fuses have a current rating (e.g., 1 A, 5 A) — if the current exceeds this value, the fuse blows.

Diodes

A diode is a component that allows current to flow in one direction only — like a one-way valve. It has two terminals: the anode (+) and cathode (−). When connected in the forward direction (anode to positive voltage), it conducts. When reversed, it blocks.

LEDs (Light-Emitting Diodes)

An LED is a special type of diode that emits light when forward current flows through it. LEDs are everywhere — indicator lights, displays, torches, and room lighting. Like all diodes, LEDs are non-ohmic and only allow current in one direction. They also require a current-limiting resistor to prevent burning out.

Ohmic vs Non-Ohmic Components

Components can be divided into two groups based on how they behave with voltage and current:

• •Ohmic components — Have a constant resistance regardless of voltage. Examples: carbon-film resistors, metal-film resistors, wire-wound resistors, and ordinary wire/conductors.
• •Non-ohmic components — Their resistance changes with the applied voltage or temperature. Examples: diodes, LEDs, transistors, thermistors (temperature-sensitive), and LDRs (light-sensitive).

Quick Reference Table

• •Battery — Provides voltage (energy source). Symbol: long/short parallel lines.
• •Wire — Connects components (conductor). Symbol: straight line.
• •Resistor — Resists current (ohmic). Symbol: zigzag or rectangle.
• •Switch — Opens/closes circuit path. Symbol: line with a gap that can close.
• •Fuse — Protects circuit (melts if overcurrent). Symbol: thin line in a box.
• •Diode — Allows current one way only (non-ohmic). Symbol: triangle with bar.
• •LED — Emits light when forward-biased (non-ohmic). Symbol: diode with arrows.