Physics — Ohm’s law and combinations of resistors

Overview

Ohm’s law links current, potential difference and resistance in a conductor at constant temperature.

Key concepts

• V = IR. Units: volt (V), ampere (A), ohm (Ω).
• Series: R = R₁ + R₂ + … ; same current through each resistor.
• Parallel: 1/R = 1/R₁ + 1/R₂ + … ; same potential difference across each.
• Power P = VI = I²R = V²/R.

Important points

• Two equal resistors in parallel give half the value of one.
• Charge is measured in coulombs: 1 C = 1 A × 1 s.

Quick revision

2 A through 10 Ω → V = 20 V. Two 4 Ω in parallel → 2 Ω.