Electric Charge & the Atom
Everything electrical begins with a property of matter so fundamental we can only describe what it does: charge.
It all starts inside the atom
Every object around you is made of atoms, and every atom is a tiny bundle of electricity. Its nucleus contains protons, each carrying a positive charge, and around the nucleus move electrons, each carrying an exactly equal and opposite negative charge. Normally the counts match, the charges cancel, and the atom looks neutral from the outside. All of electrical engineering comes down to one trick: separating and moving those charges on purpose.
Charge is measured in coulombs (C). A single electron carries a minuscule −1.602 × 10⁻¹⁹ C, so one coulomb corresponds to about 6.24 × 10¹⁸ electrons — six billion billion of them. Charge comes in whole-electron steps and it is never created or destroyed, only moved around.
The force between charges
Two charges push or pull on each other without touching: like charges repel, opposite charges attract. In 1785, Charles-Augustin de Coulomb measured exactly how strong that force is:
Two things matter here. The force grows with the product of the charges — double either one and the force doubles. And it falls with the square of the distance: pull the charges twice as far apart and the force drops to a quarter. This inverse-square law is the same mathematical shape as gravity — but electricity is astonishingly stronger. The electric repulsion between two protons is about 10³⁶ times larger than their gravitational attraction. The only reason you don’t notice this colossal force in daily life is that positive and negative charges are almost perfectly mixed everywhere.
Conductors and insulators
In metals like copper, the outermost electron of each atom isn’t attached to any particular atom — it drifts freely through the whole material as part of a shared “sea” of electrons. Materials like that are conductors: charge can move through them. In glass, rubber or plastic, every electron is held tightly to its atom, so charge stays put — those are insulators. A wire is exactly this idea made practical: a conducting copper core wearing an insulating plastic jacket so the charge goes only where we want it.
Rub a balloon on your hair and you scrape electrons from hair onto balloon. The balloon becomes negative, your hair positive — and Coulomb’s force makes your hair reach for the balloon. A doorknob shock in winter is the same thing at higher stakes: your body accumulated extra charge, and it all jumped the gap at once.
Static tricks are fun, but engineering needs charge that moves continuously and controllably. For that, we first need a way to give charges energy — which is the next lesson.
⚡ Lab — Coulomb's Force Playground
Two charges, one law. Drag them around and watch the force respond.
- Drag a charge slowly closer — notice how violently the force grows near the end (that’s the 1/r²).
- Make both charges positive, then give them opposite signs. Watch the arrows flip.
- Set either charge to 0 µC. What happens to the force?