Resistors
A resistor limits current flow. Fixed resistors have a set value; potentiometers (variable resistors) can be adjusted.
Voltage divider: Two resistors in series. Voltage across each is proportional to its resistance: V₁ = V_total × R₁ / (R₁ + R₂)
Color code bands on resistors encode their value in ohms (digits, multiplier, tolerance).