Basic Electrical and Electronics Engineering: quick revision, 15 bites

Ohm's Law: The Foundation of All Circuit Analysis

One equation rules every circuit.

Ohm's law states that the current through a conductor is **directly proportional to voltage** and **inversely proportional to resistance** — the single most used relationship in electrical engineering.

Takeaway. If you know any two of V, I, R, you can always find the third.

Core Electrical Quantities You Must Know

Voltage, current, resistance — know the trio.

Takeaway. These four quantities describe almost every electrical circuit problem.

Electrical Power and Energy Formulas

Power is how fast energy is used.

Takeaway. Power tells you how fast energy is consumed; energy is power multiplied by time.

AC vs DC: Two Ways Electricity Flows

AC wiggles, DC goes straight.

Takeaway. Mains power is AC because it transmits efficiently; batteries give DC.

Series vs Parallel Circuits

Same components, very different behavior.

Takeaway. Home wiring uses parallel so each device works independently.

Active vs Passive Components

Some components give energy, some take it.

Takeaway. Active components need a power source; passive ones don't.

Semiconductors: The Heart of Electronics

Not quite a conductor, not quite an insulator.

Takeaway. Controlling semiconductor conductivity is what makes modern electronics possible.

How a PN Junction Diode Works

One-way valve for electricity.

Takeaway. A diode conducts only when forward biased — it's a one-way current gate.

Don't Confuse Current and Voltage

They're not the same thing.

Takeaway. Voltage is across, current is through — always.

Kirchhoff's Laws for Circuit Analysis

Two rules solve any circuit.

Takeaway. KCL is about charge conservation; KVL is about energy conservation.

Why Your Phone Charger Has a Rectifier

AC in, DC out — every time.

Takeaway. Diodes in a rectifier turn AC into the DC your devices need.

Remember Ohm's Law Triangle

Cover the one you want.

Draw a triangle with **V** on top, **I** and **R** at the bottom. Cover the unknown — if you cover V, you see I × R; cover I, you see V ÷ R; cover R, you see V ÷ I.

Takeaway. The V-I-R triangle gives you all three forms of Ohm's law instantly.

Standard Mains Voltage Worldwide

50 or 60 Hz — know your region.

Takeaway. Mains voltage and frequency vary by country — always check before using appliances abroad.

Exam Tip: Always Check Units

Units catch more marks than formulas.

Takeaway. Most numerical mistakes in exams come from unit mismatches, not wrong formulas.

The First Transistor Changed Everything

One device replaced thousands of tubes.

The first working transistor was demonstrated at Bell Labs in **1947**. It replaced bulky vacuum tubes, enabling smaller, faster, and cheaper electronics — leading directly to modern computers and smartphones.

Takeaway. The transistor is the single most important invention in modern electronics.