MEPX
Chapter 1 of 10All chapters
  1. 1Charge and current
  2. 2Voltage
  3. 3Resistance and Ohm law
  4. 4Series and parallel
  5. 5Power and energy
  6. 6Components
  7. 7AC and DC
  8. 8Electrical safety
  9. 9Reading a circuit diagram
  10. 10Everyday electricity

Chapter 1 of 10

Charge and current

What is actually moving.

Flow

Current is charge passing a point per second, measured in amperes. In a wire it is electrons drifting slowly, while the signal itself travels near the speed of light.

  • Conventional current is drawn from positive to negative, opposite to electron flow.
  • The convention predates knowing about electrons and is harmless once known.

Conductors and insulators

Metals hold electrons loosely and conduct. Plastics and glass hold them tightly and insulate. Semiconductors sit between the two and can be switched, which is what makes computing possible.