Electricity from First Principles
Charge & Current
12 min · 2 worked examples · 3 questionsFree
What is actually moving in a wire, and why an amp is just a rate.
After this lesson you can
- Say what current physically is, and what is moving
- Convert between charge, current and time
- Explain why conventional current runs the wrong way
Charge is a property of matter
Electric charge is a fundamental property, like mass. It comes in two kinds, which we call positive and negative, and the rule is simple: like charges repel, opposite charges attract.
Charge is measured in coulombs (C). One electron carries a tiny negative charge of about 1.6 × 10⁻¹⁹ C. Turn that around and one coulomb is the charge of roughly 6.24 × 10¹⁸ electrons, over six billion billion of them. Charge is quantised, meaning it only ever comes in whole multiples of that electron charge; you cannot have half an electron's worth.
In the full lesson
- Charge is a property of matter
- Current is charge in motion
- Electrons are slower than you think
- Conventional current
Free with an account. Read it, work the examples, answer the questions, then build it in the simulator.