Electric Charge — The Basics: Positive, Negative and Conservation
Electric charge: what it is, positive and negative, conductors vs insulators, charging methods, and conservation of charge.
Quick answer
Electric charge is a fundamental property of matter — like mass, but with two flavors. Positive and negative charges attract; like charges repel. Its flow is electric current.
Unit: coulomb (C)
Example: Rub a balloon on your hair: electrons transfer to the balloon, giving it negative charge — enough to stick to a wall by attracting opposite charges in the paint.
What you will learn
- Define electric charge and its two types
- Classify materials as conductors or insulators
- Describe charging by friction, conduction and induction
- State the conservation of charge
Charge: a fundamental property
Electric charge is a fundamental property of matter, as basic as mass. Every proton carries positive charge, every electron carries negative charge, and neutrons carry none.
The rules are beautifully simple:
- Opposite charges attract — positive pulls negative.
- Like charges repel — positive pushes positive away.
All of electricity — from static cling to power grids — is just charge obeying these two rules at enormous scale.
Positive, negative, and neutral
Charge comes in exactly two types, labeled positive (+) and negative (−):
- An object with equal protons and electrons is neutral — charges cancel.
- Extra electrons → negatively charged.
- Missing electrons → positively charged (protons themselves rarely move).
'Positive' and 'negative' are historical accidents — Franklin's guess — but the math works regardless. What matters is that there are two opposite kinds.
Conductors vs insulators
Materials divide by how freely charge moves through them:
- Conductors (copper, aluminum, salt water): electrons roam freely. Charge spreads instantly across the whole object.
- Insulators (rubber, glass, dry wood): electrons are locked to atoms. Charge stays where you put it — which is why static builds up on insulators.
- Semiconductors (silicon): in between, and controllable — the basis of all electronics.
Power cords are conductors wrapped in insulators: the copper carries current, the rubber keeps it away from you.
How objects get charged
Neutral objects become charged three ways:
- Friction (triboelectric): rubbing transfers electrons — balloon on hair, shoes on carpet.
- Conduction: touching a charged object shares charge — like pouring water between cups.
- Induction: bringing a charged object near (not touching) rearranges charges inside a conductor — the near side attracts opposite charge. Ground the far side and the object keeps a net charge after you remove the inducer.
Charge is conserved
The deepest rule: charge is never created or destroyed, only moved or separated.
Rubbing a rod doesn't manufacture charge — it steals electrons from the cloth, leaving equal and opposite charges on the two. Every lightning bolt, battery, and static shock is charge relocating, with the universe's total always balancing to zero net change.
Conservation of charge is as fundamental as conservation of energy. Whenever charge seems to appear, look for the equal opposite charge left behind.
Variables and units
| Symbol | Name | Unit | Meaning |
|---|---|---|---|
| Charge | C | Amount of electric charge | |
| Elementary charge | C | Charge of a single electron (negative) or proton (positive) |
Common mistakes
Electrons carry current in wires, but positive ions carry it in batteries, plasmas, and your nerves. Conventional current is even defined as flowing positive — opposite to electron motion.
Charge is conserved — circuits circulate it. What devices consume is energy, which the charge delivers as it drops through voltage.
Same charge, different behavior: static is charge at rest (built up), current is charge in motion. Lightning is just a very dramatic current.
Real-world applications
Photocopiers and laser printers charge drums electrostatically, then attract toner exactly where the charge pattern says.
Lightning rods give charge an easy path to ground, protecting structures from billion-volt discharges.
Industrial painting uses charged paint droplets that wrap around grounded car bodies for perfectly even coats.
Frequently asked questions
What is the unit of electric charge?
The coulomb (C) — the charge of about 6.24 × 10¹⁸ electrons. Everyday static shocks involve mere microcoulombs.
What is the charge of one electron?
1.602 × 10⁻¹⁹ coulombs, negative. It's the smallest free charge in nature — all ordinary charges are whole multiples of it.
Can electric charge be created?
Never created or destroyed — only separated or moved. Rubbing a balloon doesn't make charge; it transfers electrons from one surface to the other.
Why do I get shocked touching a doorknob in winter?
You stripped electrons off the carpet (or vice versa). Touching the doorknob lets them rush back — the tiny spark is that current jumping the air gap.