U — Voltage [V]
Electrical pressure
The "pressure" that pushes electric charge through a circuit. Higher voltage → more force. Measured in Volts (V). Example: AA battery = 1.5 V, USB = 5 V, mains = 230 V.
I — Current [A]
Flow of charge
The amount of electric charge flowing per second. Like water flow in a pipe. Measured in Amperes (A). Small circuits use milliamps (mA). LED typically needs 10–20 mA.
R — Resistance [Ω]
Opposition to flow
How much a component resists current flow. Higher R → less current for the same voltage. Measured in Ohms (Ω). A resistor limits current to protect components.
P — Power [W]
Energy per second
The rate at which energy is consumed or dissipated as heat. P = U × I. Measured in Watts (W). A resistor dissipating too much power will overheat and fail.