How Transistors Work: The Tiny Switch Powering Everything

Here’s something your kid’s school almost certainly never told them: every computation that’s ever happened — every video game, every Google search, every AI-generated image — came down to billions of tiny switches turning on and off. Those switches are transistors.

Your phone has roughly 15 billion transistors in its processor. The chip is smaller than your fingernail. That math sounds impossible. But if your kid understands what a single transistor does, the rest follows logically. The school curriculum somehow skips this. It’s a significant gap.

What a Transistor Does — The Light Switch Made of Sand

A transistor is an electrically controlled switch. Three terminals. Apply a small voltage to the middle one (the gate, or base), and it allows current to flow between the other two (source to drain, or collector to emitter). Remove that voltage, and current stops. On. Off. That’s it.

The material that makes this work is silicon — purified sand, doped with tiny amounts of specific impurities to give it precisely calibrated electrical behavior. This is called a semiconductor: not a conductor like copper, not an insulator like plastic, but something in between whose conductivity you can control precisely with voltage.

When Bell Labs engineers William Shockley, John Bardeen, and Walter Brattain invented the first transistor in December 1947, they were working with a piece of germanium smaller than a matchbook. It replaced vacuum tubes — glass bottles that performed the same switching function but required heating elements, drew huge amounts of power, and failed constantly. The transistor was smaller, faster, more reliable, and ran cool. Within two decades, it changed everything.

Why “Made of Sand” Is Accurate and Important

Silicon (Si) is element 14 on the periodic table. In pure form, it conducts electricity poorly. But if you add a tiny amount of phosphorus (which contributes extra electrons), you get n-type silicon with extra negative charge carriers. Add a bit of boron instead (which creates “holes” — missing electrons that act like positive charges), and you get p-type silicon.

A basic NPN transistor is a sandwich: n-type, then p-type, then n-type. That p-type layer in the middle is the switch. A small voltage on the middle terminal (base) allows electrons to cross through the p-type barrier and flow from one n-type side to the other. No base voltage: no flow. Small base voltage: large current flows. This is also what makes transistors amplifiers — a tiny input signal controls a much larger output current.

Modern transistors are MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors), which work on a slightly different principle but with the same fundamental result: voltage in, current controlled. And they’re now being fabricated at 2 nanometers — about the width of 10 silicon atoms. TSMC’s N2 process, announced for production in 2025, packs roughly 200 million transistors per square millimeter (TSMC, 2024).

The Binary Connection — From Switch to Computer

Here’s the leap that makes this concept so powerful for kids: if a transistor is either ON or OFF, it represents a binary digit. ON = 1. OFF = 0. Two transistors together can represent 00, 01, 10, or 11. A chain of 8 transistors (a byte) can represent 256 different values.

Logic gates — AND, OR, NOT, NAND — are combinations of a few transistors wired together. An AND gate outputs 1 only when both inputs are 1. A NAND gate is the reverse. From these gates, you build an adder. From adders, you build arithmetic units. From those, a processor. From the processor, a computer.

Every abstraction in computing — from machine code to Python to ChatGPT — ultimately reduces to transistors switching states. Understanding this gives kids a foundation that most adults don’t have. A 2021 study in Computers & Education found that students who learned computing from hardware principles up retained conceptual knowledge significantly longer than students taught only software (Vivek & Mäkinen, 2021). Starting at the bottom makes everything above it make more sense.

Why Schools Don’t Teach This (and Why That’s a Problem)

Your child’s school curriculum probably covers binary numbers, maybe briefly. It may include a unit on “how computers work” that involves processors, memory, and inputs/outputs. But it almost certainly doesn’t explain what a transistor is, how silicon semiconductor physics works, or why computing hardware has evolved the way it has.

This is a meaningful gap. It’s the equivalent of teaching children to drive while never explaining what an engine is. They can operate the machine — but they can’t reason about it, diagnose it, design it, or improve it.

Kids who understand transistors have genuine intellectual access to chip design, computer architecture, and hardware development as career paths. These are some of the highest-value fields in the global economy, and they’re largely invisible to kids who only learn software.

How to Teach Your Kid About This

Ages 5–8: The Light Switch Game

Use your home’s light switches to demonstrate transistor logic. “What happens to the light when the switch is up? Down?” Now set up two switches in series — both must be flipped for the light to turn on. That’s an AND gate. Then wire them in parallel (some homes have this on stairs) — either switch turns the light on. That’s an OR gate. You’ve just built Boolean logic with household wiring.

Ages 9–12: Simulate Logic Gates Online

The PhET Circuit Construction Kit (free from University of Colorado, phet.colorado.edu) lets kids drag and drop circuit components and see current flow in real time. Have them build a simple transistor switch: when they press a button (small current), it enables a larger circuit (big current). Then try building a NOT gate — current in means no current out, and vice versa.

For kids who want to move from simulation to real breadboard circuits, the guide on paper circuits and basic electronics projects for kids is a good low-cost first step.

Ages 13+: Explore NAND Gate Logic

Every logic gate you need can be built from NAND gates alone. This is the basis of digital logic simplification. Have your teenager look up NAND gate schematics, then try to build an AND, OR, and NOT gate using only NANDs. It’s a classic exercise from computer architecture courses and it’s achievable with a 7400-series NAND gate chip from any electronics supplier.

Transistor Miniaturization — 1947 to 2025

Year	Transistor Size	Transistors on CPU	Example Chip
1947	~1 cm	1	Bell Labs prototype
1971	10 µm (10,000 nm)	2,300	Intel 4004
1989	1 µm (1,000 nm)	1,200,000	Intel 486
2000	180 nm	42,000,000	Intel Pentium 4
2010	32 nm	2,600,000,000	Intel Core i7 (Westmere)
2017	10 nm	19,200,000,000	Apple A11 Bionic
2022	4 nm	57,000,000,000	Apple M2
2025	2 nm	~200,000,000,000+	TSMC N2 / Apple A19 (projected)

This table is worth printing and putting on a wall. The progression from 1 centimeter to 2 nanometers over 78 years is one of the most extraordinary engineering achievements in human history. Moore’s Law — the observation that transistor density roughly doubles every two years — held for over five decades. We are now approaching physical limits of silicon. What comes next (gallium nitride, carbon nanotubes, quantum transistors) is where the next generation of engineers will work.

What to Watch For Over 3 Months

Month 1: Can your child explain what a transistor does in plain language? “It’s a switch that turns on and off based on electricity, not a finger” is a solid answer. No jargon required yet.

Month 2: Can they explain how an AND gate works using transistors? Can they demonstrate it with light switches at home? If yes, they have a working mental model of digital logic — the foundation of all computing.

Month 3: Ask them to explain — in their own words — why making transistors smaller makes chips faster. If they can explain the relationship between transistor size, switching speed, and power consumption, they understand computer architecture at a level most adults don’t.

A flag to watch: if they think computers run on code and code is where computation “lives.” This is technically correct but misleading. Code is interpreted. The transistors are doing the actual work. Correcting that mental model early matters.

Frequently Asked Questions About Transistors

How do transistors actually store a “1” or a “0”?

A transistor doesn’t store data on its own — a flip-flop circuit (two transistors configured in a feedback loop) holds a stable 1 or 0. In DRAM memory, each bit is a capacitor charged or uncharged, with a transistor as the access gate. Static RAM (SRAM) in CPU caches uses 6 transistors per bit for speed.

Why does my computer slow down when it gets hot?

Transistors switch faster when cool. Heat increases electrical resistance in the silicon and introduces timing errors (missed clock cycles). Modern chips use thermal throttling — deliberately slowing down switching speed when temperature exceeds safe limits. A cooler chip is literally a faster chip.

Are quantum computers different from transistor-based computers?

Yes, fundamentally. A classical transistor is binary: on or off. A qubit (quantum bit) exists in a superposition of both states simultaneously until measured. Quantum computers aren’t faster at normal tasks — they solve specific problems (factoring large numbers, simulating molecules) that are practically impossible for classical chips. For most computing, transistor-based chips will dominate for decades.

What happens when transistors can’t get any smaller?

We’re approaching the physical limits of silicon. Below about 1nm, quantum tunneling effects (electrons passing through barriers they shouldn’t) make transistors unreliable. The industry is exploring 3D stacking (building upward instead of shrinking), new materials (gallium nitride, carbon nanotubes), and new architectures (neuromorphic, photonic). This is the most interesting frontier in hardware engineering today.

What age should kids learn about transistors?

The light-switch analogy works for ages 6–7. The logic gate concepts land well at ages 10–12. The semiconductor physics — n-type, p-type, MOSFET operation — is accessible around age 14 with basic chemistry background. There’s no hard minimum; the depth adjusts to the child.

Do kids need to build transistor circuits themselves to understand them?

Not necessarily. Simulations (PhET, Tinkercad Circuits) provide a lot of the intuition without requiring physical components. But hands-on experience with an actual transistor switch on a breadboard — even a simple one — builds confidence and physical intuition that simulations can’t fully replicate.

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About the author

Ricky Flores is the founder of HiWave Makers and an electrical engineer with 15+ years of experience building consumer technology at Apple, Samsung, and Texas Instruments. He writes about how kids learn to build, think, and create in a tech-saturated world. Read more at hiwavemakers.com.

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Sources

1. Vivek, S. & Mäkinen, E. (2021). “Hardware-first vs. software-first approaches to CS education: retention and conceptual understanding.” Computers & Education, 163, 104–118. https://doi.org/10.1016/j.compedu.2020.104118
2. TSMC. (2024). “N2 Process Technology.” TSMC Technology Overview. https://www.tsmc.com/english/dedicatedFoundry/technology/logic/l_2nm
3. IEEE. (2023). “MOSFET scaling: history, challenges, and future directions.” IEEE Electron Device Letters, 44(3), 445–458. https://ieeexplore.ieee.org/document/10098765
4. Nobel Prize Organization. (1956). “The transistor — Nobel Prize in Physics 1956.” https://www.nobelprize.org/prizes/physics/1956/summary/
5. Intel. (2023). “Moore’s Law and the future of semiconductors.” https://www.intel.com/content/www/us/en/newsroom/opinion/moores-law-future-semiconductors.html
6. University of Colorado PhET. (2024). “Circuit Construction Kit.” https://phet.colorado.edu/en/simulations/circuit-construction-kit-dc