Electronics from Zero · EPISODE 2 · 2:52

Ohm's Law with Real Examples

One rule works in every circuit you will ever build: Ohm's law, V = I × R. Learn it in under 3 minutes with real examples — a kettle, a toaster, your phone cable and your own body (and why water and electricity never mix).

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What you'll learn

Double the voltage → double the current (5 V + 220 Ω ≈ 23 mA, 10 V ≈ 45 mA). Double the resistance → half the current.
Ohm's law: current = voltage ÷ resistance. Written V = I × R (I = current, from "intensity"). Georg Ohm, 1827.
The triangle trick: cover the one you want. I = V ÷ R · R = V ÷ I · V = I × R.
9 V and 1,000 Ω → 9 mA. A kettle: 230 V ÷ 24 Ω ≈ 9.6 A (India, UK, Europe) · 120 V ÷ 10 Ω = 12 A (USA, Canada).
Your body: dry skin ≈ 100,000 Ω → a 9 V battery pushes only 0.09 mA (you feel nothing). Wet skin ≈ 1,000 Ω → a wall socket pushes over 100 mA (230 mA at 230 V, 120 mA at 120 V) — enough to stop a heart. Never touch mains.
A toaster on 120 V pulling 10 A → its heating wire is 12 Ω.
A phone cable ≈ 0.2 Ω: 3 A × 0.2 Ω = 0.6 V lost as heat. A cheap, thin cable has more resistance → slower charging.