Foundations — Read and interpret circuit schematic symbols

Everything below is built in order. Nothing is used before it is drawn. Read top to bottom.

0. Charge — the stuff that moves

Before any symbol makes sense, we need the thing the symbols push around.

1. Current — how fast charge flows

Why do we even need this symbol $I$? Because to say what a component does, we must talk about "how much flow," and $I$ is that number.

Look at the arrow in the figure: it leaves the $+$ side, loops all the way round, and returns to the $-$ side. That single arrow is the "which way does the water flow" answer, and it decides which way an LED must point later.

2. Voltage and potential — the push

3. Node — the most important idea on the whole page

In the figure, every dot painted the same colour is the same node — one shared potential — even though the wires bend and stretch. The schematic doesn't care about the bends; it cares only about "same colour or not."

4. The wire — a node extender

Why call it a "node extender"? Because a wire adds no function — it just spreads one potential across the drawing. That is exactly why the whole of Section 3 works.

5. The junction dot vs the crossing — connected or not?

This is the single detail that flips a working circuit into a broken one, so it gets its own figure.

6. The battery — the pump (source of push)

Why is the pump the first component to find when reading? Because it sets the direction of current (out of $+$) and the total push the rest of the circuit shares.

7. The resistor — the narrow pipe

8. Ground — the "sea level" reference

Why do we need it? Because voltage is always a difference (Section 2). To hand out single numbers like "$5$ V here," we must agree where $0$ is — ground is that agreement.

9. The switch — a controllable break

A switch is how we decide whether the loop is complete. Open the switch and the pump has nowhere to push.

10. The capacitor — the storage wall

Picture it as a wall the water pushes against: it fills up, then flow stops. It matters because it behaves totally differently from a resistor even though both sit "in the path."

11. The diode / LED — the one-way gate

12. The lamp — a glowing resistor

13. Putting drops together — the loop rule

This is the accounting rule that lets the parent note write $I=\frac{\mathcal{E}-V_{LED}}{R}$ — the resistor drops whatever push the battery didn't hand to the LED.

Prerequisite map

Equipment checklist

Test yourself — reveal only after you have answered.