The Transistor: A Little Tap for Current

1. What your child learns and why

Almost every electronic device contains transistors. Your child discovers the simplest idea about them: a transistor is like a tap for current. It has three legs — the base (the “handle”), the collector and the emitter. A small current into the base controls a larger current from the collector to the emitter; the small current does not carry the big one, it only “lets it through”. The tap also has a limit: the most current that can flow depends on the battery and the resistor. The numbers are examples.

2. Three questions for dinner

• “With a light touch of a handle you can release a lot of water from a tap. Who carries the water — the hand or the hose?”
• “If a tap is fully open, will more water flow if you keep turning it? What decides how much flows?”
• “Which small word or gesture from you can “open a tap” for something big in another person?”

3. 10–15 minutes together, no screen — “Tap and Hose”

1. Form a “hose”: one person by the basket, one in the middle (the tap) and one by the cup. The paper balls are passed from hand to hand — that is the big current.
2. A fourth person is the small current: they never touch the balls, they only gently touch the tap's shoulder. A light touch — 1 ball, a firmer touch — 3 balls, no touch — nothing.
3. Play for 20 seconds and count the balls in the cup. Swap roles. Ask: “Who carries the balls? Who decides how many?”

4. What success looks like

• Your child points to the base, collector and emitter on a drawing and says that the small current controls the big one without carrying it.
• They explain to you (or a younger child) why the tap has a limit. They draw a “small signal → big action” device for someone at home — a drawing only, no personal data.

5. Common difficulties

• “If it amplifies 100 times, why isn't the LED hundreds of times brighter?” → run the simulator: the tap reaches a limit.
• They want a real circuit right away → “First on paper and in the simulator; a real one together, with a small battery.”

6. Safety

7. Where to go next

Previous lesson: DB-EL-08 “A Radio Without a Battery: The Crystal Set” · Next track: DB-IB-01 “Passwords Even a Dragon Can't Guess” · Before this: DB-EL-02 “Switch, LED and Why a Resistor”