Every electrical and electronic system—whether it is a mobile phone, inverter, motor control panel, computer, TV, or industrial machine—is built using a small set of fundamental components. These are known as basic electrical and electronic components. Understanding them is the first and most important step for anyone entering the world of electricity, electronics, or engineering.
Beginners often see circuit diagrams full of strange symbols and feel overwhelmed. But the truth is simple: each symbol represents a component with a clear purpose—controlling current, storing energy, switching signals, or transferring power. Once you understand these basics, complex circuits start to make sense naturally.
This article is a complete, beginner-friendly, long-term guide covering the six most important components:
- Resistor
- Capacitor
- Diode
- Inductor
- Transistor
- Transformer
You will learn what each component is, its symbol, how it works, where it is used, and real-life examples. This guide is ideal for students, ITI trainees, diploma holders, engineering beginners, electricians, and self-learners worldwide.
Key takeaway: If you master these six components, you can understand almost 80% of basic electrical and electronic circuits.
What Are Electrical and Electronic Components?
Electrical and electronic components are physical devices used in circuits to control the flow of electricity, store energy, convert signals, or perform switching and amplification.
They are broadly classified into:
Passive components – Do not amplify signals (Resistor, Capacitor, Inductor)
1. Resistor
What Is a Resistor?
A resistor is a passive component that limits or controls the flow of electric current in a circuit.
Resistor Symbol
A zig-zag or rectangular line in circuit diagrams.
Unit of Resistance
Ohm (Ω)How a Resistor Works
When current flows through a resistor, part of the electrical energy is converted into heat, reducing the current according to Ohm’s Law:
V = I × R
Types of Resistors
- Fixed resistor
- Variable resistor (potentiometer)
- Thermistor
- LDR (Light Dependent Resistor)
Applications of Resistors
- Current limiting
- Voltage division
- Biasing transistors
- Protecting LEDs
- Signal conditioning
Real-life example: Volume control knob in audio systems.
2. Capacitor
What Is a Capacitor?
A capacitor is a passive component that stores electrical energy in an electric field.
Capacitor Symbol
Two parallel lines (for non-polarized) or one curved line (for polarized).
Unit of Capacitance
Farad (F)Commonly used: µF, nF, pF
How a Capacitor Works
A capacitor charges when voltage is applied and discharges when voltage is removed. It blocks DC after charging but allows AC signals to pass.
Types of Capacitors
- Ceramic
- Electrolytic
- Tantalum
- Film capacitor
Applications of Capacitors
- Power supply filtering
- Signal coupling and decoupling
- Timing circuits
- Motor starting
- Noise suppression
Real-life example: Smoothing ripple in phone chargers.
3. Diode
What Is a Diode?
A diode is a semiconductor device that allows current to flow in only one direction.
Diode Symbol
A triangle pointing toward a vertical line.
How a Diode Works
- Forward bias: Conducts current
- Reverse bias: Blocks current
Types of Diodes
- PN junction diode
- Zener diode
- LED (Light Emitting Diode)
- Schottky diode
Applications of Diodes
- Rectification (AC to DC)
- Reverse polarity protection
- Voltage regulation
- Signal clipping
Real-life example: Rectifier circuit in adapters and chargers.
4. Inductor
What Is an Inductor?
An inductor is a passive component that stores energy in a magnetic field when current flows through it.
Inductor Symbol
A coil-shaped symbol.
Unit of Inductance
Henry (H)How an Inductor Works
Inductors oppose changes in current. When current increases or decreases, the inductor resists the change by inducing voltage.
Types of Inductors
- Air-core
- Iron-core
- Ferrite-core
Applications of Inductors
- Choke coils
- Filters
- SMPS circuits
- Transformers (basic element)
Real-life example: Noise suppression in power supplies.
5. Transistor
What Is a Transistor?
A transistor is an active semiconductor device used to amplify or switch electronic signals.
Transistor Symbol
Three-terminal symbol representing:
- Base
- Emitter
- Collector
Types of Transistors
- BJT (NPN, PNP)
- MOSFET
- IGBT
How a Transistor Works
A small input signal at the base/gate controls a much larger current at the output.
Applications of Transistors
- Amplifiers
- Electronic switches
- Digital logic circuits
- Microprocessors
- Power control
Real-life example: Switching circuits inside computers and mobile phones.
6. Transformer
What Is a Transformer?
A transformer is a power device that increases or decreases AC voltage using electromagnetic induction.
Transformer Symbol
Two coils separated by a magnetic core.
How a Transformer Works
AC voltage in the primary winding creates a magnetic field that induces voltage in the secondary winding.
Types of Transformers
- Step-up transformer
- Step-down transformer
- Isolation transformer
Applications of Transformers
- Power transmission
- Voltage conversion
- Electrical isolation
- Chargers and adapters
Real-life example: Mobile phone charger.
Comparison Table: Basic Electrical Components
| Component | Function | Stores Energy | Active/Passive |
|---|---|---|---|
| Resistor | Limits current | No | Passive |
| Capacitor | Stores electric energy | Yes (electric field) | Passive |
| Diode | One-way current | No | Active |
| Inductor | Stores magnetic energy | Yes (magnetic field) | Passive |
| Transistor | Amplify/switch | No | Active |
| Transformer | Change AC voltage | Yes (magnetic coupling) | Power device |
Common Beginner Mistakes
- Confusing capacitor and inductor functions
- Using diode in wrong direction
- Applying DC to transformer
- Ignoring resistor power rating
- Incorrect transistor pin connections
FAQs – Basic Electrical & Electronic Components
1. Why are resistors used in circuits?
They control current and protect components from damage.
2. Can a capacitor store DC?
It stores DC temporarily but blocks continuous DC flow.
3. What happens if a diode is connected wrongly?
Current will not flow, and the circuit may fail.
4. Why are inductors heavy?
Due to copper winding and magnetic core.
5. What is the main use of a transistor?
Signal amplification and electronic switching.
6. Can a transformer work on DC supply?
No, transformers require AC to operate.
7. Which component stores energy longest?
Capacitor (electric) and inductor (magnetic), depending on circuit.
8. Are all transformers step-down?
No, they can be step-up, step-down, or isolation.
9. What is the most used component in electronics?
The resistor.
10. Are these components still relevant today?
Yes, they are the foundation of all modern electronics.
