Understanding Ohm's Law — The Foundation of Every Circuit

By Charles Inyende



If you're new to electrical engineering, Ohm's Law is the first rule you'll meet — and the one you'll never stop using.

The basics

Ohm's Law states that the current flowing through a conductor is directly proportional to the voltage across it, and inversely proportional to its resistance:

V = I × R

Where:

V = Voltage (volts)

I = Current (amps)

R = Resistance (ohms)

Why it matters in real work

Every time you size a cable, choose a breaker, or troubleshoot a circuit that's tripping, you're using Ohm's Law whether you realize it or not. A breaker trips because current (I) has exceeded what the circuit's resistance and voltage can safely support. A dim bulb might mean a voltage drop along a long cable run — again, Ohm's Law explains why.

A practical example

Say you have a 240V supply feeding a heater with 20 ohms of resistance:

I = V / R = 240 / 20 = 12 amps

Now you know to use a breaker and cable rated for at least 12A, with some safety margin.

Common mistake beginners make

Forgetting that resistance changes with temperature. A cold heating element has lower resistance than a hot one — which is why some appliances draw a brief surge of current when first switched on.

Try it yourself: Take any household appliance with its wattage and voltage printed on the label. Use P = V × I to find the current, then R = V / I to find its resistance. It's a simple way to turn Ohm's Law from theory into something you can verify with your own hands.

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