What Even Is Electricity?
Reasoning from first principles — the way great engineers do — applied to the electrons under your fingertips.
Musk's Rocket Science · Part 1 — Electricity Basics · Chapter 1 · 18 min read
A wind turbine spins offshore, and within milliseconds that mechanical motion becomes current flowing through an inter-array cable. A grid-scale BESS container discharges 4 megawatt-hours in under an hour to cover an evening demand peak. An EV plugged into a fast charger adds 200 kilometres of range in twenty minutes. All of this feels like a very modern kind of magic — but it is not. At the most fundamental level it is all just electrons moving in a hurry, obeying a small handful of precise, knowable laws that have not changed since long before any of these technologies existed.
Electricity is the single most useful force humans have ever learned to tame, and yet almost nobody who uses it every day could explain what it actually is, or do the arithmetic behind it. This chapter fixes that from scratch, by reasoning from first principles: break a thing down to the most fundamental truths you can be sure of, then build back up with logic and numbers rather than analogy alone.
1.1 — Everything is made of tiny solar systems
Zoom into anything around you — your phone, the air, your own hand — and eventually you hit atoms. Zoom into an atom, and you find three characters.
Table 1.1 — The three subatomic particles
| Particle | Charge | Relative mass | Location | Role in electricity |
|---|---|---|---|---|
| Proton | +1 (positive) | 1,836× | Nucleus | Stays put — defines which element the atom is |
| Neutron | 0 (neutral) | 1,839× | Nucleus | Adds mass and nuclear stability; no direct electrical role |
| Electron | −1 (negative) | 1× (reference) | Orbiting shells | The one that moves — this is electricity |
Here is a lithium atom — fitting, since lithium is the “Li” in every LiFePO4 cell.
In plain English
Think of the nucleus as the sun and the electrons as planets. The inner planets are locked into tight orbits and rarely leave. But the outermost planet is barely holding on — a small nudge and it drifts off to visit a neighbouring atom. That nudge is exactly what a battery, a wall socket, or a lightning bolt provides.
1.1.1 — Charge is quantised: the elementary charge
Here is the first genuinely deep fact: electric charge does not come in just any amount. It comes in fixed, indivisible packets. Every electron carries exactly the same tiny negative charge, and every proton exactly the opposite. That smallest possible unit is the elementary charge, denoted e.
e = 1.602176634 × 10⁻¹⁹ Coulombs
Any charge you will ever measure — on a balloon, in a lightning bolt, inside a battery — is a whole-number multiple of this value. You cannot have half an electron’s worth of charge. This was proven experimentally in 1909 by Robert Millikan’s oil-drop experiment, in which he suspended tiny charged oil droplets between two charged plates and measured the charge needed to hold each against gravity. Every measurement came out a whole multiple of the same tiny number.
Technical framing
Quantisation of charge underpins essentially all of classical electromagnetism, and it underpins concepts later in this series — such as why battery capacity, measured in amp-hours, is fundamentally a count of how many billions of these elementary charge packets a cell can move in and out during a cycle.
1.1.2 — Coulomb's Law: the force behind every spark
Charges push and pull on each other. Like charges repel; opposite charges attract. In 1785 the French physicist Charles-Augustin de Coulomb measured exactly how strong that push or pull is, and found a beautifully simple relationship: the force depends on the size of the two charges, and falls off with the square of the distance between them.
F = k · (q₁ q₂) / r²
F is force in Newtons, q₁ and q₂ are the charges in Coulombs, r is the separation in metres, and k is Coulomb’s constant, approximately 8.99 × 10⁹ N·m²/C².
Worked example 1.1 — Force between two electrons
Two electrons sit 0.3 nanometres apart — roughly one atomic diameter, a realistic spacing inside a molecule.
q₁ = q₂ = 1.6 × 10⁻¹⁹ C, r = 0.3 × 10⁻⁹ m
F = (8.99 × 10⁹) × (1.6×10⁻¹⁹ × 1.6×10⁻¹⁹) / (0.3×10⁻⁹)²
F ≈ 2.56 × 10⁻⁹ N (about 2.56 nano-Newtons)
That sounds tiny, and in human terms it is. But an electron weighs about 9.1 × 10⁻³¹ kg, so that “tiny” force produces an acceleration of roughly F/m ≈ 2.8 × 10²¹ m/s². This is why electrons respond to electric fields essentially instantaneously on human timescales, even though the forces involved are minuscule in absolute terms.
Why this matters later
Coulomb’s Law is the reason a battery works at all. Inside every cell, chemistry deliberately creates a surplus of electrons at one terminal and a shortage at the other. That charge imbalance is voltage — and Coulomb’s Law is the underlying force description of why electrons want to rush from the surplus side to the shortage side the moment you give them a path.
1.2 — So what is electricity, really?
Electricity is the coordinated movement of loosely-held valence electrons from one atom to the next. That is the whole secret. When billions of electrons all drift in the same direction through a material — a copper wire, a battery, your own nervous system — we call that flow electric current.
I = Q / t
I is current in Amperes, Q is total charge passed in Coulombs, and t is time in seconds.
One Amp means one Coulomb of charge passing a point every second — which, given the elementary charge above, works out to roughly 6.24 × 10¹⁸ electrons per second. An almost incomprehensibly large number of electrons, moving at what turns out to be a very unglamorous everyday speed.
1.2.1 — The most counter-intuitive fact in this chapter
Here is a question worth sitting with. If a light switch turns a bulb on instantly, the electrons inside the wire must be flying at close to the speed of light… right?
Wrong, and by an enormous margin. The average speed of individual electrons drifting through a copper wire — the drift velocity — is astonishingly slow. We can calculate it directly.
I = n · q · v_d · A
n is free electrons per cubic metre (a property of the material), q is the elementary charge, v_d is drift velocity, and A is the wire’s cross-sectional area.
Worked example 1.2 — How fast do electrons actually move?
Take a typical household copper wire: cross-sectional area A ≈ 3.3 × 10⁻⁶ m² (about 2mm diameter), carrying a modest current of 2A. Copper has roughly n ≈ 8.5 × 10²⁸ free electrons per cubic metre.
v_d = I / (n · q · A)
v_d = 2 / (8.5×10²⁸ × 1.6×10⁻¹⁹ × 3.3×10⁻⁶)
v_d ≈ 0.00044 m/s — less than half a millimetre per second
At that speed a single electron would take roughly 19 minutes to travel one metre of wire. Slower than a garden snail.
So why does the light turn on instantly? Because what propagates down the wire near the speed of light is not any individual electron — it is the electric field itself. Think of a long tube already completely packed with marbles: push one marble in at one end and a marble pops out the other almost instantly, not because that specific marble travelled the tube, but because the push propagates through the packed line immediately. A copper wire is already full of free electrons. Flipping the switch does not wait for electrons to travel from switch to bulb; it starts the whole packed line moving together, everywhere, at once.
Technical framing
This is the distinction between drift velocity (how fast individual charge carriers physically move, on average) and signal propagation velocity (how fast a change in the electric field travels through the conductor, which is a large fraction of the speed of light, set by the wire’s geometry and surrounding dielectric). Nearly every intuition failure in early electromagnetism traces back to conflating these two very different velocities.
1.3 — The water analogy, with the right caveats
Electricity is invisible, which makes it hard to picture. Engineers commonly lean on a shortcut: water flowing through a pipe.
Table 1.2 — The water–electricity analogy
| Water system | Electrical system |
|---|---|
| Water | Electric charge (electrons) |
| Water flow rate (litres/second) | Electric current (Amps) |
| Water pressure pushing the flow | Voltage (Volts) |
| Pipe narrowness slowing the flow | Resistance (Ohms) |
| A water tank | A battery |
| A closed tap | An open circuit (no current flows) |
Imagine a water tank on a rooftop connected to a tap downstairs by a pipe. The height of the tank creates pressure — the water wants to flow down. Open the tap and water rushes through. A narrower pipe restricts the flow even at the same pressure. Swap tank for battery, pressure for voltage and pipe for wire, and you have understood the shape of the relationship we formalise as Ohm’s Law in Chapter 3.
Where the analogy breaks down
Water is genuinely incompressible and flows as a bulk fluid at essentially the pressure-driven speed. Electrons, as section 1.2.1 just showed, barely move at all — it is the field, not the charge carriers, that moves fast. The water analogy is excellent for building intuition about voltage, current and resistance as concepts, but do not extend it to reasoning about propagation speed.
1.4 — Real life is full of electricity — across the entire energy stack
The chart and table below span an enormous voltage range — from a nerve impulse to a bulk HVDC transmission link — plotted on a logarithmic scale where each step is roughly a hundred times bigger than the last.
Table 1.3 — Voltage across the modern energy stack
| System | Approx. voltage | What's actually happening |
|---|---|---|
| Nerve impulse in your body | ~70 mV | Sodium and potassium ions crossing nerve cell membranes |
| PEM electrolyser cell (green hydrogen) | ~2.0V | The operating voltage of a single proton-exchange-membrane cell splitting water into hydrogen and oxygen |
| Li-ion cell (EV / gigafactory grade) | ~3.7V | A single NMC cell as manufactured at gigafactory scale for EV packs |
| Data centre 48V DC bus | 48V | Standard internal DC distribution voltage inside modern hyperscale data centres |
| 16S LiFePO4 e-rickshaw pack | 51.2V | 16 LiFePO4 cells at 3.2V nominal each, wired in series — the packs this series is ultimately about |
| EV traction battery pack (400V class) | 400V | A typical passenger EV pack, built from roughly 100 cells in series |
| Medium-voltage grid distribution feeder | 33,000V | A common regional distribution voltage, stepping power down toward substations and homes |
| HVDC transmission link (±500kV class) | 500,000V | Long-distance bulk power transmission, often moving renewable generation from remote sites to demand centres |
| Lightning bolt | Up to 100,000,000V | The same underlying physics as a static discharge, at planetary scale |
In plain English
The jump from a 400V EV pack to a 33,000V distribution feeder to a 500,000V HVDC link is not arbitrary. It is the same design logic at every step: raising voltage lets the same amount of power move with less current, which sharply cuts resistive losses in the cabling — as Chapter 4 shows precisely.
This is your first hint of a theme that runs through the entire series: voltage tells you how hard electricity is pushing; current tells you how much is actually flowing — and it is current, not voltage, that does the real damage or dictates the real cabling and loss budget. We unpack this fully in Chapter 2.
1.5 — Static electricity: Coulomb's Law in daily life
Static electricity is simply what happens when electrons transfer between two materials that touch or rub together, leaving one with a surplus of electrons (negatively charged) and the other with a deficit (positively charged). Whether a material tends to grab electrons or give them up is remarkably consistent, and has been catalogued as the triboelectric series.
Worked example 1.3 — Why battery gigafactories and semiconductor fabs are so obsessive about ESD
A technician walking across a factory floor in low-humidity conditions, wearing ungrounded footwear, can accumulate a static charge of several thousand volts — the same triboelectric charging mechanism as any two dissimilar materials sliding against each other.
By Coulomb’s Law, that charged body creates a strong local electric field. The instant it approaches a grounded, conductive object — an exposed battery cell terminal, or a bare semiconductor die on a PCB — the field can be strong enough to force a rapid discharge current through whatever sits in between.
A modern SiC or GaN power semiconductor, the same devices used in EV inverters and fast chargers, can be permanently destroyed by an electrostatic discharge (ESD) event lasting only nanoseconds and carrying a fraction of a joule — utterly imperceptible to the person who caused it.
This is why gigafactory clean rooms and semiconductor fabs mandate grounded wrist straps, ESD-safe flooring and humidity control: not superstition, but a direct, quantifiable consequence of Coulomb’s Law and charge quantisation from sections 1.1.1 and 1.1.2.
The same underlying physics — triboelectric charge separation followed by a Coulomb’s Law-driven discharge — also governs industrial electrostatic precipitators used to strip particulates from power-plant flue gas, and, at planetary scale, thunderclouds, where colliding ice crystals build up the charge imbalance that eventually discharges as lightning.
1.6 — Conductors, insulators and why copper wins
Not every material lets electrons wander freely. Some hold their valence electrons in a death grip; others practically hand them out.
Table 1.4 — Conductors, insulators and semiconductors
| Material type | Behaviour | Real-world examples |
|---|---|---|
| Conductor | Valence electrons are loosely held and move easily | Copper, silver, aluminium, gold, saltwater, the human body |
| Insulator | Valence electrons are tightly bound and do not move | Rubber, glass, dry wood, plastic, air (usually) |
| Semiconductor | Behaves as insulator or conductor depending on conditions | Silicon, germanium — the basis of every computer chip and every BMS on the market |
In plain English
Every high-current cable in a BESS container or an EV powertrain is copper, not silver. Silver is actually a slightly better conductor than copper — roughly 6.30 × 10⁷ S/m against copper’s 5.96 × 10⁷ S/m — but copper is far cheaper and almost as good, which is why it remains the default for busbars, windings and interconnects across the entire energy industry.
Technical framing
Semiconductors are the most commercially important entry in Table 1.4. Silicon has powered electronics for decades, but the fastest-growing segment of power electronics — EV inverters and onboard chargers, fast-charging stations, and utility-scale Power Conversion Systems — is increasingly built on wide-bandgap semiconductors like Silicon Carbide (SiC) and Gallium Nitride (GaN). Their wider electronic bandgap lets them switch at higher frequencies and higher temperatures with lower losses than silicon, translating directly into smaller, lighter, more efficient inverters and chargers — a materials-science consequence of the same conductor/insulator/semiconductor spectrum introduced here.
1.7 — A very short history of electricity
Electricity was not invented. It was discovered, piece by piece, over roughly 2,600 years — and most of it in the last 250.
- •~600 BCE — Thales of Miletus. Rubbed amber with cloth and noticed it attracted feathers. He had stumbled onto static electricity. The Greek word for amber, elektron, is where the word “electricity” itself comes from.
- •1752 — Benjamin Franklin. His kite experiment (dangerous — please do not recreate it) demonstrated that lightning is electrical in nature, the same phenomenon as the static shock off a doorknob, at a colossal scale.
- •1800 — Alessandro Volta. Built the first true battery, the voltaic pile: alternating zinc and copper discs separated by brine-soaked cloth. For the first time, humans had a steady, controllable source of current rather than a single spark. The volt is named after him.
- •1831 — Michael Faraday. Discovered that a moving magnet near a wire induces current — electromagnetic induction. This single discovery underlies every electric generator and, in reverse, every electric motor on Earth, including every wind turbine and EV traction motor operating today.
- •1879 — Thomas Edison. Commercialised the incandescent bulb, kicking off mass electrification, running on direct current.
- •1888 — Nikola Tesla. Patented the AC induction motor, the technology that let alternating current win the War of Currents against Edison’s DC for long-distance transmission — the full story is Chapter 4.
- •1991 — Sony. Shipped the first commercial lithium-ion battery — the direct ancestor of every gigafactory-produced EV, BESS and e-rickshaw cell manufactured today.
- •2020s — Gigafactories and grid-scale BESS. Global lithium-ion manufacturing capacity surpasses 1 TWh per year, driven simultaneously by EV adoption, utility-scale battery storage and data centre backup power — a scale-up of roughly seven orders of magnitude from Volta’s original voltaic pile, in just over two centuries.
Chapter summary
- ✓Everything is made of atoms; atoms have protons (+), neutrons (neutral) and electrons (−).
- ✓Charge is quantised — it comes in whole multiples of the elementary charge, e = 1.602 × 10⁻¹⁹ C.
- ✓Coulomb’s Law, F = k·q₁q₂/r², governs attraction and repulsion between all charges, and is the underlying reason batteries push electrons at all.
- ✓Electricity is the flow of loosely-held valence electrons moving from atom to atom. Current I = Q/t.
- ✓Drift velocity is astonishingly slow — often under a millimetre per second — while the signal driving it propagates at a large fraction of the speed of light. Two very different speeds.
- ✓Conductors let electrons flow easily; insulators block them; semiconductors sit in between and power every modern chip.
- ✓Static electricity is electron transfer between materials, governed by the triboelectric series and explained by Coulomb’s Law.
- ✓Electricity spans an enormous voltage range across the modern energy stack, from 70mV nerve impulses to 500kV HVDC links and 100-million-volt lightning bolts.
- ✓Humanity’s understanding of electricity built up over 2,600+ years, from rubbed amber to the gigafactory-scale lithium-ion cell.
Test your understanding
- 1Explain, using the triboelectric series and Coulomb’s Law, why battery gigafactories and semiconductor fabs mandate grounded wrist straps and ESD-safe flooring.
- 2If electrons in a wire only drift a fraction of a millimetre per second, why does a light switch turn a bulb on instantly?
- 3Two point charges of +2μC and −3μC sit 5cm apart. Using Coulomb’s Law, is the force between them attractive or repulsive, and roughly how strong is it? (k = 8.99×10⁹ N·m²/C²)
- 4A 400V-class EV traction pack is built from roughly 100 Li-ion cells at 3.7V each in series. Is its voltage more or less than a medium-voltage (33kV) distribution feeder — and by roughly what factor?
- 5Why do you think copper, not silver — a slightly better conductor — is used in almost all high-current wiring across battery packs, data centres and the grid?
- 6Challenge: a wire carries 5A. Using I = n·q·v_d·A with copper’s electron density n ≈ 8.5 × 10²⁸ /m³ and a cross-section of 1.0 × 10⁻⁶ m², calculate the drift velocity. How long would an electron take to drift one metre?
Frequently asked questions
What is electricity, in simple terms?+
Electricity is the coordinated movement of loosely-held valence electrons from one atom to the next. Every atom has electrons in orbital shells; the outermost ones are only weakly attached, and when billions of them drift in the same direction through a material we call that flow electric current.
How fast do electrons actually move in a wire?+
Astonishingly slowly. In a typical 2mm household copper wire carrying 2A, the drift velocity works out to roughly 0.00044 metres per second — less than half a millimetre per second. A single electron would take about 19 minutes to travel one metre, slower than a garden snail.
If electrons move so slowly, why does a light turn on instantly?+
Because what travels near the speed of light is not any individual electron — it is the electric field. A copper wire is already packed with free electrons, so flipping the switch starts the whole line moving at once, like pushing a marble into a tube that is already full. Drift velocity and signal propagation velocity are two completely different speeds.
What is the elementary charge?+
Electric charge is quantised, meaning it only comes in whole multiples of one indivisible packet. That packet is the elementary charge, e = 1.602176634 × 10⁻¹⁹ Coulombs. Every electron carries exactly minus one of it and every proton exactly plus one. Millikan proved this experimentally in 1909 with his oil-drop experiment.
What is Coulomb’s Law?+
Coulomb’s Law describes the force between two electric charges: F = k · q₁q₂ / r², where k is approximately 8.99 × 10⁹ N·m²/C². Like charges repel, opposite charges attract, and the force falls off with the square of the distance — the same mathematical shape as gravity, but vastly stronger at atomic scales.
Why is copper used for wiring instead of silver?+
Silver is a slightly better conductor — about 6.30 × 10⁷ S/m against copper’s 5.96 × 10⁷ S/m — but copper is far cheaper and almost as good. That cost-to-conductivity ratio is why copper remains the default for busbars, windings and interconnects across the entire energy industry, from BESS containers to EV powertrains.
Why do battery gigafactories and semiconductor fabs require ESD protection?+
A technician walking across a factory floor in low humidity with ungrounded footwear can accumulate several thousand volts of static charge through ordinary triboelectric charging. By Coulomb’s Law that charged body creates a strong local field, and approaching a grounded conductor can force a discharge lasting only nanoseconds. That is enough to permanently destroy a modern SiC or GaN power semiconductor, so grounded wrist straps, ESD-safe flooring and humidity control are mandatory.
Why do power grids step voltage up to hundreds of thousands of volts?+
Because for a fixed amount of power, P = V × I means raising voltage proportionally lowers current, and resistive loss in the cabling scales with the square of current. That single trade-off explains the whole voltage ladder — a 400V EV pack, a 33kV distribution feeder, a ±500kV HVDC link — each step chosen to move power with acceptable losses over its distance.
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Musk's Rocket Science is an original educational series explaining the physics and chemistry behind everyday electricity and battery technology. Figures and worked examples use standard physical constants and representative real-world values for illustration.