We built before we understood. The first lamps were lit by hands like yours, wired by feel, bright before anyone could say why. Start there. Make light.
⟨ transmission ends ⟩In the next few minutes you will build your first circuit and light your first LED. No formulas today, no theory: just three parts, two wires, and your hands. Everything you will ever build starts exactly like this.
On the bench below sit a battery, a resistor (the small striped barrel), and an LED, a little light on two legs. Almost everything is already connected. One wire is still loose, and its free end is yours.
Every circuit obeys one rule: electricity moves only in a closed loop, and the whole loop acts together. Close the gap and watch it happen.
A 9 V battery, a 470 Ω resistor, a red LED. Closed, the loop carries about 15 mA: comfortable for this LED. The moving dots are the flow; they start along the whole loop at once because the push arrives everywhere at nearly the speed of light.
The LED is a diode: it passes the flow one way and blocks the other, long leg toward the battery’s + side. Turn it around and see.
Same loop, same parts, nothing removed. Backwards, the LED stands like a closed door, and because the loop is one whole, the flow stops everywhere at once, not just at the LED.
The resistor is the LED’s guardian: it holds the flow down to what the LED can survive. Pull it out and watch what the bare battery does.
Without the resistor, only the battery’s own small inner resistance is left to hold the flow back, and it leaps to far beyond what the LED tolerates. A real LED dies like this in well under a second; the flare is slowed here so you can watch it. Press ↺ for a fresh LED.
A flare, then dead for good: that is what the bare battery does to an unguarded LED. We chose this resistor for you. In The Three Numbers you learn to choose it yourself, for any LED and any battery.
Before you go on, meet your three parts properly: what each one looks like in real life, and the symbol that stands for it in a circuit drawing.
When you are ready, test yourself. Two situations from real benches:
Your LED stays dark after you close the loop. What do you try first?
A friend wants to leave the resistor out “so the light will be brighter”. What do you tell them?
You have built a working circuit, killed an LED on purpose, and learned the rule that governs every board you will ever touch. Next, the three numbers behind all of it: how hard the battery pushes, how much flows, and how much the resistor resists, so the next resistor is one you choose yourself.
Lesson 1 done.
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